diff --git a/Makefile.msc b/Makefile.msc
index e8efe58296..6fc4c83390 100644
--- a/Makefile.msc
+++ b/Makefile.msc
@@ -52,6 +52,13 @@ MINIMAL_AMALGAMATION = 0
 USE_STDCALL = 0
 !ENDIF
 
+# Set this non-0 to use structured exception handling (SEH) for WAL mode
+# in the core library.
+#
+!IFNDEF USE_SEH
+USE_SEH = 0
+!ENDIF
+
 # Set this non-0 to have the shell executable link against the core dynamic
 # link library.
 #
@@ -389,6 +396,13 @@ OPT_FEATURE_FLAGS = $(OPT_FEATURE_FLAGS) -DSQLITE_ENABLE_MATH_FUNCTIONS
 OPT_FEATURE_FLAGS = $(OPT_FEATURE_FLAGS) -DSQLITE_ENABLE_RBU=1
 !ENDIF
 
+# Should structured exception handling (SEH) be enabled for WAL mode in
+# the core library?
+#
+!IF $(USE_SEH)!=0
+OPT_FEATURE_FLAGS = $(OPT_FEATURE_FLAGS) -DSQLITE_USE_SEH=1
+!ENDIF
+
 # These are the "extended" SQLite compilation options used when compiling for
 # the Windows 10 platform.
 #
diff --git a/autoconf/Makefile.msc b/autoconf/Makefile.msc
index 09daa867ec..24154dd5d8 100644
--- a/autoconf/Makefile.msc
+++ b/autoconf/Makefile.msc
@@ -52,6 +52,13 @@ MINIMAL_AMALGAMATION = 0
 USE_STDCALL = 0
 !ENDIF
 
+# Set this non-0 to use structured exception handling (SEH) for WAL mode
+# in the core library.
+#
+!IFNDEF USE_SEH
+USE_SEH = 0
+!ENDIF
+
 # Set this non-0 to have the shell executable link against the core dynamic
 # link library.
 #
@@ -311,6 +318,13 @@ OPT_FEATURE_FLAGS = $(OPT_FEATURE_FLAGS) -DSQLITE_ENABLE_MATH_FUNCTIONS
 OPT_FEATURE_FLAGS = $(OPT_FEATURE_FLAGS) -DSQLITE_ENABLE_RBU=1
 !ENDIF
 
+# Should structured exception handling (SEH) be enabled for WAL mode in
+# the core library?
+#
+!IF $(USE_SEH)!=0
+OPT_FEATURE_FLAGS = $(OPT_FEATURE_FLAGS) -DSQLITE_USE_SEH=1
+!ENDIF
+
 # These are the "extended" SQLite compilation options used when compiling for
 # the Windows 10 platform.
 #
diff --git a/ext/wasm/GNUmakefile b/ext/wasm/GNUmakefile
index 3990d227c1..ed5550e7b8 100644
--- a/ext/wasm/GNUmakefile
+++ b/ext/wasm/GNUmakefile
@@ -179,7 +179,6 @@ SQLITE_OPT = \
   -DSQLITE_OMIT_DEPRECATED \
   -DSQLITE_OMIT_UTF16 \
   -DSQLITE_OMIT_SHARED_CACHE \
-  -DSQLITE_OMIT_WAL \
   -DSQLITE_THREADSAFE=0 \
   -DSQLITE_TEMP_STORE=2 \
   -DSQLITE_OS_KV_OPTIONAL=1 \
@@ -187,6 +186,12 @@ SQLITE_OPT = \
   -DSQLITE_USE_URI=1 \
   -DSQLITE_WASM_ENABLE_C_TESTS \
   -DSQLITE_C=$(sqlite3.c)
+#SQLITE_OPT += -DSQLITE_DEBUG
+# Enabling SQLITE_DEBUG will break sqlite3_wasm_vfs_create_file()
+# (and thus sqlite3_js_vfs_create_file()). Those functions are
+# deprecated and alternatives are in place, but this crash behavior
+# can be used to find errant uses of sqlite3_js_vfs_create_file()
+# in client code.
 
 .NOTPARALLEL: $(sqlite3.h)
 $(sqlite3.h):
diff --git a/ext/wasm/api/sqlite3-api-glue.js b/ext/wasm/api/sqlite3-api-glue.js
index 572efeed5c..60050461c7 100644
--- a/ext/wasm/api/sqlite3-api-glue.js
+++ b/ext/wasm/api/sqlite3-api-glue.js
@@ -608,6 +608,7 @@ globalThis.sqlite3ApiBootstrap.initializers.push(function(sqlite3){
     ["sqlite3_wasm_db_vfs", "sqlite3_vfs*", "sqlite3*","string"],
     ["sqlite3_wasm_vfs_create_file", "int",
      "sqlite3_vfs*","string","*", "int"],
+    ["sqlite3_wasm_posix_create_file", "int", "string","*", "int"],
     ["sqlite3_wasm_vfs_unlink", "int", "sqlite3_vfs*","string"]
   ];
 
diff --git a/ext/wasm/api/sqlite3-api-prologue.js b/ext/wasm/api/sqlite3-api-prologue.js
index 3b29041c37..ca5d1c44ff 100644
--- a/ext/wasm/api/sqlite3-api-prologue.js
+++ b/ext/wasm/api/sqlite3-api-prologue.js
@@ -1357,6 +1357,74 @@ globalThis.sqlite3ApiBootstrap = function sqlite3ApiBootstrap(
   };
 
   /**
+     If the current environment supports the POSIX file APIs, this routine
+     creates (or overwrites) the given file using those APIs. This is
+     primarily intended for use in Emscripten-based builds where the POSIX
+     APIs are transparently proxied by an in-memory virtual filesystem.
+     It may behave diffrently in other environments.
+
+     The first argument must be either a JS string or WASM C-string
+     holding the filename. Note that this routine does _not_ create
+     intermediary directories if the filename has a directory part.
+
+     The 2nd argument may either a valid WASM memory pointer, an
+     ArrayBuffer, or a Uint8Array. The 3rd must be the length, in
+     bytes, of the data array to copy. If the 2nd argument is an
+     ArrayBuffer or Uint8Array and the 3rd is not a positive integer
+     then the 3rd defaults to the array's byteLength value.
+
+     Results are undefined if data is a WASM pointer and dataLen is
+     exceeds data's bounds.
+
+     Throws if any arguments are invalid or if creating or writing to
+     the file fails.
+
+     Added in 3.43 as an alternative for the deprecated
+     sqlite3_js_vfs_create_file().
+  */
+  capi.sqlite3_js_posix_create_file = function(filename, data, dataLen){
+    let pData;
+    if(data && wasm.isPtr(data)){
+      pData = data;
+    }else if(data instanceof ArrayBuffer || data instanceof Uint8Array){
+      pData = wasm.allocFromTypedArray(data);
+      if(arguments.length<3 || !util.isInt32(dataLen) || dataLen<0){
+        dataLen = data.byteLength;
+      }
+    }else{
+      SQLite3Error.toss("Invalid 2nd argument for sqlite3_js_posix_create_file().");
+    }
+    try{
+      if(!util.isInt32(dataLen) || dataLen<0){
+        SQLite3Error.toss("Invalid 3rd argument for sqlite3_js_posix_create_file().");
+      }
+      const rc = wasm.sqlite3_wasm_posix_create_file(filename, pData, dataLen);
+      if(rc) SQLite3Error.toss("Creation of file failed with sqlite3 result code",
+                               capi.sqlite3_js_rc_str(rc));
+    }finally{
+       wasm.dealloc(pData);
+    }
+  };
+
+  /**
+     Deprecation warning: this function does not work properly in
+     debug builds of sqlite3 because its out-of-scope use of the
+     sqlite3_vfs API triggers assertions in the core library.  That
+     was unfortunately not discovered until 2023-08-11. This function
+     is now deprecated and should not be used in new code.
+
+     Alternative options:
+
+     - "unix" VFS and its variants can get equivalent functionality
+       with sqlite3_js_posix_create_file().
+
+     - OPFS: use either sqlite3.oo1.OpfsDb.importDb(), for the "opfs"
+       VFS, or the importDb() method of the PoolUtil object provided
+       by the "opfs-sahpool" OPFS (noting that its VFS name may differ
+       depending on client-side configuration). We cannot proxy those
+       from here because the former is necessarily asynchronous and
+       the latter requires information not available to this function.
+
      Creates a file using the storage appropriate for the given
      sqlite3_vfs.  The first argument may be a VFS name (JS string
      only, NOT a WASM C-string), WASM-managed `sqlite3_vfs*`, or
@@ -1402,9 +1470,13 @@ globalThis.sqlite3ApiBootstrap = function sqlite3ApiBootstrap(
        VFS nor the WASM environment imposes requirements which break it.
 
      - "opfs": uses OPFS storage and creates directory parts of the
-       filename.
+       filename. It can only be used to import an SQLite3 database
+       file and will fail if given anything else.
   */
   capi.sqlite3_js_vfs_create_file = function(vfs, filename, data, dataLen){
+    config.warn("sqlite3_js_vfs_create_file() is deprecated and",
+                "should be avoided because it can lead to C-level crashes.",
+                "See its documentation for alternative options.");
     let pData;
     if(data){
       if(wasm.isPtr(data)){
@@ -1432,7 +1504,7 @@ globalThis.sqlite3ApiBootstrap = function sqlite3ApiBootstrap(
       if(rc) SQLite3Error.toss("Creation of file failed with sqlite3 result code",
                                capi.sqlite3_js_rc_str(rc));
     }finally{
-      wasm.dealloc(pData);
+       wasm.dealloc(pData);
     }
   };
 
diff --git a/ext/wasm/api/sqlite3-vfs-opfs.c-pp.js b/ext/wasm/api/sqlite3-vfs-opfs.c-pp.js
index 58c511082c..93482505ac 100644
--- a/ext/wasm/api/sqlite3-vfs-opfs.c-pp.js
+++ b/ext/wasm/api/sqlite3-vfs-opfs.c-pp.js
@@ -1168,11 +1168,41 @@ const installOpfsVfs = function callee(options){
       doDir(opt.directory, 0);
     };
 
-    //TODO to support fiddle and worker1 db upload:
-    //opfsUtil.createFile = function(absName, content=undefined){...}
-    //We have sqlite3.wasm.sqlite3_wasm_vfs_create_file() for this
-    //purpose but its interface and name are still under
-    //consideration.
+    /**
+       Asynchronously imports the given bytes (a byte array or
+       ArrayBuffer) into the given database file.
+
+       It very specifically requires the input to be an SQLite3
+       database and throws if that's not the case.  It does so in
+       order to prevent this function from taking on a larger scope
+       than it is specifically intended to. i.e. we do not want it to
+       become a convenience for importing arbitrary files into OPFS.
+
+       Throws on error. Resolves to the number of bytes written.
+    */
+    opfsUtil.importDb = async function(filename, bytes){
+      if(bytes instanceof ArrayBuffer) bytes = new Uint8Array(bytes);
+      const n = bytes.byteLength;
+      if(n<512 || n%512!=0){
+        toss("Byte array size is invalid for an SQLite db.");
+      }
+      const header = "SQLite format 3";
+      for(let i = 0; i < header.length; ++i){
+        if( header.charCodeAt(i) !== bytes[i] ){
+          toss("Input does not contain an SQLite database header.");
+        }
+      }
+      const [hDir, fnamePart] = await opfsUtil.getDirForFilename(filename, true);
+      const hFile = await hDir.getFileHandle(fnamePart, {create:true});
+      const sah = await hFile.createSyncAccessHandle();
+      sah.truncate(0);
+      const nWrote = sah.write(bytes, {at: 0});
+      sah.close();
+      if(nWrote != n){
+        toss("Expected to write "+n+" bytes but wrote "+nWrote+".");
+      }
+      return nWrote;
+    };
 
     if(sqlite3.oo1){
       const OpfsDb = function(...args){
@@ -1182,6 +1212,7 @@ const installOpfsVfs = function callee(options){
       };
       OpfsDb.prototype = Object.create(sqlite3.oo1.DB.prototype);
       sqlite3.oo1.OpfsDb = OpfsDb;
+      OpfsDb.importDb = opfsUtil.importDb;
       sqlite3.oo1.DB.dbCtorHelper.setVfsPostOpenSql(
         opfsVfs.pointer,
         function(oo1Db, sqlite3){
diff --git a/ext/wasm/api/sqlite3-wasm.c b/ext/wasm/api/sqlite3-wasm.c
index 94b16d7500..fcfbc06929 100644
--- a/ext/wasm/api/sqlite3-wasm.c
+++ b/ext/wasm/api/sqlite3-wasm.c
@@ -141,9 +141,6 @@
 #ifndef SQLITE_OMIT_UTF16
 # define SQLITE_OMIT_UTF16 1
 #endif
-#ifndef SQLITE_OMIT_WAL
-# define SQLITE_OMIT_WAL 1
-#endif
 #ifndef SQLITE_OS_KV_OPTIONAL
 # define SQLITE_OS_KV_OPTIONAL 1
 #endif
@@ -295,7 +292,7 @@ SQLITE_WASM_EXPORT void * sqlite3_wasm_pstack_ptr(void){
 */
 SQLITE_WASM_EXPORT void sqlite3_wasm_pstack_restore(unsigned char * p){
   assert(p>=PStack.pBegin && p<=PStack.pEnd && p>=PStack.pPos);
-  assert(0==(p & 0x7));
+  assert(0==((unsigned long long)p & 0x7));
   if(p>=PStack.pBegin && p<=PStack.pEnd /*&& p>=PStack.pPos*/){
     PStack.pPos = p;
   }
@@ -1353,6 +1350,13 @@ int sqlite3_wasm_db_serialize( sqlite3 *pDb, const char *zSchema,
 ** This function is NOT part of the sqlite3 public API. It is strictly
 ** for use by the sqlite project's own JS/WASM bindings.
 **
+** ACHTUNG: it was discovered on 2023-08-11 that, with SQLITE_DEBUG,
+** this function's out-of-scope use of the sqlite3_vfs/file/io_methods
+** APIs leads to triggering of assertions in the core library. Its use
+** is now deprecated and VFS-specific APIs for importing files need to
+** be found to replace it. sqlite3_wasm_posix_create_file() is
+** suitable for the "unix" family of VFSes.
+**
 ** Creates a new file using the I/O API of the given VFS, containing
 ** the given number of bytes of the given data. If the file exists, it
 ** is truncated to the given length and populated with the given
@@ -1398,7 +1402,14 @@ int sqlite3_wasm_vfs_create_file( sqlite3_vfs *pVfs,
   int rc;
   sqlite3_file *pFile = 0;
   sqlite3_io_methods const *pIo;
-  const int openFlags = SQLITE_OPEN_READWRITE | SQLITE_OPEN_CREATE;
+  const int openFlags = SQLITE_OPEN_READWRITE | SQLITE_OPEN_CREATE
+#if 0 && defined(SQLITE_DEBUG)
+    | SQLITE_OPEN_MAIN_JOURNAL
+    /* ^^^^ This is for testing a horrible workaround to avoid
+       triggering a specific assert() in os_unix.c:unixOpen(). Please
+       do not enable this in real builds. */
+#endif
+    ;
   int flagsOut = 0;
   int fileExisted = 0;
   int doUnlock = 0;
@@ -1464,6 +1475,34 @@ int sqlite3_wasm_vfs_create_file( sqlite3_vfs *pVfs,
   return rc;
 }
 
+/**
+** This function is NOT part of the sqlite3 public API. It is strictly
+** for use by the sqlite project's own JS/WASM bindings.
+**
+** Creates or overwrites a file using the POSIX file API,
+** i.e. Emscripten's virtual filesystem. Creates or truncates
+** zFilename, appends pData bytes to it, and returns 0 on success or
+** SQLITE_IOERR on error.
+*/
+SQLITE_WASM_EXPORT
+int sqlite3_wasm_posix_create_file( const char *zFilename,
+                                    const unsigned char * pData,
+                                    int nData ){
+  int rc;
+  FILE * pFile = 0;
+  int fileExisted = 0;
+  size_t nWrote = 1;
+
+  if( !zFilename || nData<0 || (pData==0 && nData>0) ) return SQLITE_MISUSE;
+  pFile = fopen(zFilename, "w");
+  if( 0==pFile ) return SQLITE_IOERR;
+  if( nData>0 ){
+    nWrote = fwrite(pData, (size_t)nData, 1, pFile);
+  }
+  fclose(pFile);
+  return 1==nWrote ? 0 : SQLITE_IOERR;
+}
+
 /*
 ** This function is NOT part of the sqlite3 public API. It is strictly
 ** for use by the sqlite project's own JS/WASM bindings.
diff --git a/ext/wasm/module-symbols.html b/ext/wasm/module-symbols.html
index 865f1b3338..c5c6bc162b 100644
--- a/ext/wasm/module-symbols.html
+++ b/ext/wasm/module-symbols.html
@@ -355,6 +355,7 @@
         sqlite3_js_db_vfs: 'wasm:/api-c-style.md#sqlite3_js_db_vfs',
         sqlite3_js_kvvfs_clear: 'wasm:/api-c-style.md#sqlite3_js_kvvfs',
         sqlite3_js_kvvfs_size: 'wasm:/api-c-style.md#sqlite3_js_kvvfs',
+        sqlite3_js_posix_create_file: 'wasm:/api-c-style.md#sqlite3_js_posix_create_file',
         sqlite3_js_rc_str: 'wasm:/api-c-style.md#sqlite3_js_rc_str',
         sqlite3_js_vfs_create_file: 'wasm:/api-c-style.md#sqlite3_js_vfs_create_file',
         sqlite3_js_vfs_list: 'wasm:/api-c-style.md#sqlite3_js_vfs_list',
diff --git a/ext/wasm/tester1.c-pp.js b/ext/wasm/tester1.c-pp.js
index c1b16d5e81..bd945dcab7 100644
--- a/ext/wasm/tester1.c-pp.js
+++ b/ext/wasm/tester1.c-pp.js
@@ -1657,7 +1657,7 @@ globalThis.sqlite3InitModule = sqlite3InitModule;
         .assert('number'===typeof rc[0])
         .assert(rc[0]|0 === rc[0] /* is small integer */);
     })
-  ////////////////////////////////////////////////////////////////////////
+    ////////////////////////////////////////////////////////////////////////
     .t({
       name: 'sqlite3_js_db_export()',
       predicate: ()=>true,
@@ -1671,13 +1671,12 @@ globalThis.sqlite3InitModule = sqlite3InitModule;
       }
     }/*sqlite3_js_db_export()*/)
     .t({
-      name: 'sqlite3_js_vfs_create_file() with db in default VFS',
+      name: 'sqlite3_js_posix_create_file()',
       predicate: ()=>true,
       test: function(sqlite3){
         const db = this.db;
-        const pVfs = capi.sqlite3_js_db_vfs(db);
-        const filename = "sqlite3_js_vfs_create_file().db";
-        capi.sqlite3_js_vfs_create_file(pVfs, filename, this.dbExport);
+        const filename = "sqlite3_js_posix_create_file.db";
+        capi.sqlite3_js_posix_create_file(filename, this.dbExport);
         delete this.dbExport;
         const db2 = new sqlite3.oo1.DB(filename,'r');
         try {
@@ -1686,7 +1685,7 @@ globalThis.sqlite3InitModule = sqlite3InitModule;
           T.assert(n>0 && db2.selectValue(sql) === n);
         }finally{
           db2.close();
-          wasm.sqlite3_wasm_vfs_unlink(pVfs, filename);
+          wasm.sqlite3_wasm_vfs_unlink(0, filename);
         }
       }
     }/*sqlite3_js_vfs_create_file()*/)
@@ -2907,7 +2906,7 @@ globalThis.sqlite3InitModule = sqlite3InitModule;
     .t({
       name: 'OPFS db sanity checks',
       test: async function(sqlite3){
-        const filename = this.opfsDbFile = 'sqlite3-tester1.db';
+        const filename = this.opfsDbFile = '/dir/sqlite3-tester1.db';
         const pVfs = this.opfsVfs = capi.sqlite3_vfs_find('opfs');
         T.assert(pVfs);
         const unlink = this.opfsUnlink =
@@ -2935,22 +2934,23 @@ globalThis.sqlite3InitModule = sqlite3InitModule;
       }
     }/*OPFS db sanity checks*/)
     .t({
-      name: 'OPFS export/import',
+      name: 'OPFS import',
       test: async function(sqlite3){
         let db;
         try {
           const exp = this.opfsDbExport;
           delete this.opfsDbExport;
-          capi.sqlite3_js_vfs_create_file("opfs", this.opfsDbFile, exp);
-          const db = new sqlite3.oo1.OpfsDb(this.opfsDbFile);
-          T.assert(6 === db.selectValue('select count(*) from p'));
+          this.opfsImportSize = await sqlite3.oo1.OpfsDb.importDb(this.opfsDbFile, exp);
+          db = new sqlite3.oo1.OpfsDb(this.opfsDbFile);
+          T.assert(6 === db.selectValue('select count(*) from p')).
+            assert( this.opfsImportSize == exp.byteLength );
         }finally{
           if(db) db.close();
         }
       }
     }/*OPFS export/import*/)
     .t({
-      name: 'OPFS utility APIs and sqlite3_js_vfs_create_file()',
+      name: '(Internal-use) OPFS utility APIs',
       test: async function(sqlite3){
         const filename = this.opfsDbFile;
         const pVfs = this.opfsVfs;
@@ -2959,8 +2959,6 @@ globalThis.sqlite3InitModule = sqlite3InitModule;
         delete this.opfsDbFile;
         delete this.opfsVfs;
         delete this.opfsUnlink;
-        unlink();
-        // Sanity-test sqlite3_js_vfs_create_file()...
         /**************************************************************
            ATTENTION CLIENT-SIDE USERS: sqlite3.opfs is NOT intended
            for client-side use. It is only for this project's own
@@ -2968,39 +2966,19 @@ globalThis.sqlite3InitModule = sqlite3InitModule;
            any time.
         ***************************************************************/
         const opfs = sqlite3.opfs;
-        const fSize = 1379;
+        const fSize = this.opfsImportSize;
+        delete this.opfsImportSize;
         let sh;
         try{
-          T.assert(!(await opfs.entryExists(filename)));
-          capi.sqlite3_js_vfs_create_file(
-            pVfs, filename, null, fSize
-          );
           T.assert(await opfs.entryExists(filename));
-          let fh = await opfs.rootDirectory.getFileHandle(filename);
+          const [dirHandle, filenamePart] = await opfs.getDirForFilename(filename, false);
+          const fh = await dirHandle.getFileHandle(filenamePart);
           sh = await fh.createSyncAccessHandle();
           T.assert(fSize === await sh.getSize());
           await sh.close();
           sh = undefined;
           unlink();
           T.assert(!(await opfs.entryExists(filename)));
-
-          const ba = new Uint8Array([1,2,3,4,5]);
-          capi.sqlite3_js_vfs_create_file(
-            "opfs", filename, ba
-          );
-          T.assert(await opfs.entryExists(filename));
-          fh = await opfs.rootDirectory.getFileHandle(filename);
-          sh = await fh.createSyncAccessHandle();
-          T.assert(ba.byteLength === await sh.getSize());
-          await sh.close();
-          sh = undefined;
-          unlink();
-
-          T.mustThrowMatching(()=>{
-            capi.sqlite3_js_vfs_create_file(
-              "no-such-vfs", filename, ba
-            );
-          }, "SQLITE_NOTFOUND: Unknown sqlite3_vfs name: no-such-vfs");
         }finally{
           if(sh) await sh.close();
           unlink();
@@ -3103,7 +3081,7 @@ globalThis.sqlite3InitModule = sqlite3InitModule;
         const conf2 = JSON.parse(JSON.stringify(sahPoolConfig));
         conf2.name += '-test2';
         const POther = await inst(conf2);
-        log("Installed second SAH instance as",conf2.name);
+        //log("Installed second SAH instance as",conf2.name);
         T.assert(0 === POther.getFileCount())
           .assert(true === await POther.removeVfs());
 
diff --git a/manifest b/manifest
index 62a3a3927c..92f7518f85 100644
--- a/manifest
+++ b/manifest
@@ -1,11 +1,11 @@
-C Fix\sa\smakefile\sdeps\sproblem\swhich\scaused\sext/jni\sbuild\sto\sfail\sif\ssqlite3.c/h\swere\snot\screated\sbeforehand.
-D 2023-08-11T20:32:40.205
+C Merge\strunk\sinto\sjni\sbranch.
+D 2023-08-11T21:24:08.276
 F .fossil-settings/empty-dirs dbb81e8fc0401ac46a1491ab34a7f2c7c0452f2f06b54ebb845d024ca8283ef1
 F .fossil-settings/ignore-glob 35175cdfcf539b2318cb04a9901442804be81cd677d8b889fcc9149c21f239ea
 F LICENSE.md df5091916dbb40e6e9686186587125e1b2ff51f022cc334e886c19a0e9982724
 F Makefile.in 5ad2d1e198306bc730f06f7545d3a8832225b1bfddbc648d97c0e0b9a35f67e9
 F Makefile.linux-gcc f3842a0b1efbfbb74ac0ef60e56b301836d05b4d867d014f714fa750048f1ab6
-F Makefile.msc 7248d860f71ab164b4cec3c415e6cc1bd9fee860c370d65bd8bb49e9572521e2
+F Makefile.msc daad4a19e0b3c3c3b79b64d4ddbf75e3f506405e8d3f3f604d6f48b26043c51f
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 F tool/mkautoconfamal.sh f62353eb6c06ab264da027fd4507d09914433dbdcab9cb011cdc18016f1ab3b8
 F tool/mkccode.tcl 86463e68ce9c15d3041610fedd285ce32a5cf7a58fc88b3202b8b76837650dbe x
-F tool/mkctimec.tcl 38e3db33210a200aae791635125052a643a27aa0619a0debf19aa9c55e1b2dde x
+F tool/mkctimec.tcl aca4b83e49aecf10368cd5d11bc4847061041ade026db5bd8da17ef201f1403b x
 F tool/mkkeywordhash.c b9faa0ae7e14e4dbbcd951cddd786bf46b8a65bb07b129ba8c0cfade723aaffd
 F tool/mkmsvcmin.tcl 8897d515ef7f94772322db95a3b6fce6c614d84fe0bdd06ba5a1c786351d5a1d
 F tool/mkopcodec.tcl 33d20791e191df43209b77d37f0ff0904620b28465cca6990cf8d60da61a07ef
@@ -2090,8 +2091,8 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
 F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
 F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
 F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
-P 6c8538d83495ce65dbd7417263b3b06dbbb2a649e9a61a743911944599d75ffc
-R 00e08242dc8443215cfb70aa39f020b2
+P 101de670774f63757180282763730aa53e70198bd7a674c27e6044632d39d22a 8a6b0c24937e855b710f97b4aea973eff53e6d43e1182842731547aa4b37db2a
+R f0a8c88fe7b9660119e5c4d560adb197
 U stephan
-Z 4a14af7dfae41cdfaa811266b607e2bd
+Z b7f921f442de7d419e4b8b5ee576c27d
 # Remove this line to create a well-formed Fossil manifest.
diff --git a/manifest.uuid b/manifest.uuid
index a98896847a..0d1edcf329 100644
--- a/manifest.uuid
+++ b/manifest.uuid
@@ -1 +1 @@
-101de670774f63757180282763730aa53e70198bd7a674c27e6044632d39d22a
\ No newline at end of file
+4f0aeeba0287e846908180eab6f7080ebe1323ebe49340771864d110e1ca5b2b
\ No newline at end of file
diff --git a/src/ctime.c b/src/ctime.c
index c853e5ba46..3687241680 100644
--- a/src/ctime.c
+++ b/src/ctime.c
@@ -60,9 +60,6 @@ static const char * const sqlite3azCompileOpt[] = {
 #ifdef SQLITE_4_BYTE_ALIGNED_MALLOC
   "4_BYTE_ALIGNED_MALLOC",
 #endif
-#ifdef SQLITE_64BIT_STATS
-  "64BIT_STATS",
-#endif
 #ifdef SQLITE_ALLOW_COVERING_INDEX_SCAN
 # if SQLITE_ALLOW_COVERING_INDEX_SCAN != 1
   "ALLOW_COVERING_INDEX_SCAN=" CTIMEOPT_VAL(SQLITE_ALLOW_COVERING_INDEX_SCAN),
@@ -399,6 +396,9 @@ static const char * const sqlite3azCompileOpt[] = {
 #ifdef SQLITE_INTEGRITY_CHECK_ERROR_MAX
   "INTEGRITY_CHECK_ERROR_MAX=" CTIMEOPT_VAL(SQLITE_INTEGRITY_CHECK_ERROR_MAX),
 #endif
+#ifdef SQLITE_LEGACY_JSON_VALID
+  "LEGACY_JSON_VALID",
+#endif
 #ifdef SQLITE_LIKE_DOESNT_MATCH_BLOBS
   "LIKE_DOESNT_MATCH_BLOBS",
 #endif
diff --git a/src/json.c b/src/json.c
index fcaa9d84b9..f8d4aa2a77 100644
--- a/src/json.c
+++ b/src/json.c
@@ -3009,7 +3009,13 @@ static void jsonValidFunc(
 ){
   JsonParse *p;          /* The parse */
   UNUSED_PARAMETER(argc);
-  if( sqlite3_value_type(argv[0])==SQLITE_NULL ) return;
+  if( sqlite3_value_type(argv[0])==SQLITE_NULL ){
+#ifdef SQLITE_LEGACY_JSON_VALID
+    /* Incorrect legacy behavior was to return FALSE for a NULL input */
+    sqlite3_result_int(ctx, 0);
+#endif
+    return;
+  }
   p = jsonParseCached(ctx, argv[0], 0, 0);
   if( p==0 || p->oom ){
     sqlite3_result_error_nomem(ctx);
diff --git a/src/pager.c b/src/pager.c
index 7f2cb5ba76..a53dc1889a 100644
--- a/src/pager.c
+++ b/src/pager.c
@@ -7729,4 +7729,10 @@ int sqlite3PagerWalFramesize(Pager *pPager){
 }
 #endif
 
+#ifdef SQLITE_USE_SEH
+int sqlite3PagerWalSystemErrno(Pager *pPager){
+  return sqlite3WalSystemErrno(pPager->pWal);
+}
+#endif
+
 #endif /* SQLITE_OMIT_DISKIO */
diff --git a/src/pager.h b/src/pager.h
index eb1306096c..10c1acd9b1 100644
--- a/src/pager.h
+++ b/src/pager.h
@@ -240,4 +240,8 @@ void sqlite3PagerRekey(DbPage*, Pgno, u16);
 # define enable_simulated_io_errors()
 #endif
 
+#ifdef SQLITE_USE_SEH
+int sqlite3PagerWalSystemErrno(Pager*);
+#endif
+
 #endif /* SQLITE_PAGER_H */
diff --git a/src/sqlite.h.in b/src/sqlite.h.in
index 2af549af21..48009b1454 100644
--- a/src/sqlite.h.in
+++ b/src/sqlite.h.in
@@ -528,6 +528,7 @@ int sqlite3_exec(
 #define SQLITE_IOERR_ROLLBACK_ATOMIC   (SQLITE_IOERR | (31<<8))
 #define SQLITE_IOERR_DATA              (SQLITE_IOERR | (32<<8))
 #define SQLITE_IOERR_CORRUPTFS         (SQLITE_IOERR | (33<<8))
+#define SQLITE_IOERR_IN_PAGE           (SQLITE_IOERR | (34<<8))
 #define SQLITE_LOCKED_SHAREDCACHE      (SQLITE_LOCKED |  (1<<8))
 #define SQLITE_LOCKED_VTAB             (SQLITE_LOCKED |  (2<<8))
 #define SQLITE_BUSY_RECOVERY           (SQLITE_BUSY   |  (1<<8))
diff --git a/src/tokenize.c b/src/tokenize.c
index e3ca9a82a2..f4d013deea 100644
--- a/src/tokenize.c
+++ b/src/tokenize.c
@@ -433,7 +433,7 @@ int sqlite3GetToken(const unsigned char *z, int *tokenType){
       testcase( z[0]=='0' );  testcase( z[0]=='1' );  testcase( z[0]=='2' );
       testcase( z[0]=='3' );  testcase( z[0]=='4' );  testcase( z[0]=='5' );
       testcase( z[0]=='6' );  testcase( z[0]=='7' );  testcase( z[0]=='8' );
-      testcase( z[0]=='9' );
+      testcase( z[0]=='9' );  testcase( z[0]=='.' );
       *tokenType = TK_INTEGER;
 #ifndef SQLITE_OMIT_HEX_INTEGER
       if( z[0]=='0' && (z[1]=='x' || z[1]=='X') && sqlite3Isxdigit(z[2]) ){
diff --git a/src/util.c b/src/util.c
index 25fd6ff597..e417034754 100644
--- a/src/util.c
+++ b/src/util.c
@@ -141,6 +141,23 @@ void sqlite3ErrorClear(sqlite3 *db){
 */
 void sqlite3SystemError(sqlite3 *db, int rc){
   if( rc==SQLITE_IOERR_NOMEM ) return;
+#ifdef SQLITE_USE_SEH
+  if( rc==SQLITE_IOERR_IN_PAGE ){
+    int ii;
+    int iErr;
+    sqlite3BtreeEnterAll(db);
+    for(ii=0; ii<db->nDb; ii++){
+      if( db->aDb[ii].pBt ){
+        iErr = sqlite3PagerWalSystemErrno(sqlite3BtreePager(db->aDb[ii].pBt));
+        if( iErr ){
+          db->iSysErrno = iErr;
+        }
+      }
+    }
+    sqlite3BtreeLeaveAll(db);
+    return;
+  }
+#endif
   rc &= 0xff;
   if( rc==SQLITE_CANTOPEN || rc==SQLITE_IOERR ){
     db->iSysErrno = sqlite3OsGetLastError(db->pVfs);
diff --git a/src/vdbeaux.c b/src/vdbeaux.c
index 44c9b1e0cd..225c8d12c9 100644
--- a/src/vdbeaux.c
+++ b/src/vdbeaux.c
@@ -3372,6 +3372,7 @@ int sqlite3VdbeHalt(Vdbe *p){
           sqlite3VdbeLeave(p);
           return SQLITE_BUSY;
         }else if( rc!=SQLITE_OK ){
+          sqlite3SystemError(db, rc);
           p->rc = rc;
           sqlite3RollbackAll(db, SQLITE_OK);
           p->nChange = 0;
diff --git a/src/wal.c b/src/wal.c
index 747cf099e3..c9d8eaebe5 100644
--- a/src/wal.c
+++ b/src/wal.c
@@ -528,7 +528,13 @@ struct Wal {
   u32 iReCksum;              /* On commit, recalculate checksums from here */
   const char *zWalName;      /* Name of WAL file */
   u32 nCkpt;                 /* Checkpoint sequence counter in the wal-header */
+#ifdef SQLITE_USE_SEH
+  u32 lockMask;              /* Mask of locks held */
+  void *pFree;               /* Pointer to sqlite3_free() if exception thrown */
+  int iSysErrno;             /* System error code following exception */
+#endif
 #ifdef SQLITE_DEBUG
+  int nSehTry;               /* Number of nested SEH_TRY{} blocks */
   u8 lockError;              /* True if a locking error has occurred */
 #endif
 #ifdef SQLITE_ENABLE_SNAPSHOT
@@ -610,6 +616,100 @@ struct WalIterator {
     sizeof(ht_slot)*HASHTABLE_NSLOT + HASHTABLE_NPAGE*sizeof(u32) \
 )
 
+/*
+** Structured Exception Handling (SEH) is a Windows-specific technique
+** for catching exceptions raised while accessing memory-mapped files.
+**
+** The -DSQLITE_USE_SEH compile-time option means to use SEH to catch and
+** deal with system-level errors that arise during WAL -shm file processing.
+** Without this compile-time option, any system-level faults that appear
+** while accessing the memory-mapped -shm file will cause a process-wide
+** signal to be deliver, which will more than likely cause the entire
+** process to exit.
+*/
+#ifdef SQLITE_USE_SEH
+#include <Windows.h>
+
+/* Beginning of a block of code in which an exception might occur */
+# define SEH_TRY    __try { \
+   assert( walAssertLockmask(pWal) && pWal->nSehTry==0 ); \
+   VVA_ONLY(pWal->nSehTry++);
+
+/* The end of a block of code in which an exception might occur */
+# define SEH_EXCEPT(X) \
+   VVA_ONLY(pWal->nSehTry--); \
+   assert( pWal->nSehTry==0 ); \
+   } __except( sehExceptionFilter(pWal, GetExceptionCode(), GetExceptionInformation() ) ){ X }
+
+/* Simulate a memory-mapping fault in the -shm file for testing purposes */
+# define SEH_INJECT_FAULT sehInjectFault(pWal) 
+
+/*
+** The second argument is the return value of GetExceptionCode() for the 
+** current exception. Return EXCEPTION_EXECUTE_HANDLER if the exception code
+** indicates that the exception may have been caused by accessing the *-shm 
+** file mapping. Or EXCEPTION_CONTINUE_SEARCH otherwise.
+*/
+static int sehExceptionFilter(Wal *pWal, int eCode, EXCEPTION_POINTERS *p){
+  VVA_ONLY(pWal->nSehTry--);
+  if( eCode==EXCEPTION_IN_PAGE_ERROR ){
+    if( p && p->ExceptionRecord && p->ExceptionRecord->NumberParameters>=3 ){
+      /* From MSDN: For this type of exception, the first element of the
+      ** ExceptionInformation[] array is a read-write flag - 0 if the exception
+      ** was thrown while reading, 1 if while writing. The second element is
+      ** the virtual address being accessed. The "third array element specifies
+      ** the underlying NTSTATUS code that resulted in the exception". */
+      pWal->iSysErrno = (int)p->ExceptionRecord->ExceptionInformation[2];
+    }
+    return EXCEPTION_EXECUTE_HANDLER;
+  }
+  return EXCEPTION_CONTINUE_SEARCH;
+}
+
+/*
+** If one is configured, invoke the xTestCallback callback with 650 as
+** the argument. If it returns true, throw the same exception that is
+** thrown by the system if the *-shm file mapping is accessed after it
+** has been invalidated.
+*/
+static void sehInjectFault(Wal *pWal){
+  int res;
+  assert( pWal->nSehTry>0 );
+
+  res = sqlite3FaultSim(650);
+  if( res!=0 ){
+    ULONG_PTR aArg[3];
+    aArg[0] = 0;
+    aArg[1] = 0;
+    aArg[2] = (ULONG_PTR)res;
+    RaiseException(EXCEPTION_IN_PAGE_ERROR, 0, 3, (const ULONG_PTR*)aArg);
+  }
+}
+
+/*
+** There are two ways to use this macro. To set a pointer to be freed
+** if an exception is thrown:
+**
+**   SEH_FREE_ON_ERROR(0, pPtr);
+**
+** and to cancel the same:
+**
+**   SEH_FREE_ON_ERROR(pPtr, 0);
+**
+** In the first case, there must not already be a pointer registered to
+** be freed. In the second case, pPtr must be the registered pointer.
+*/
+#define SEH_FREE_ON_ERROR(X,Y) \
+  assert( (X==0 || Y==0) && pWal->pFree==X ); pWal->pFree = Y
+
+#else
+# define SEH_TRY          VVA_ONLY(pWal->nSehTry++);
+# define SEH_EXCEPT(X)    VVA_ONLY(pWal->nSehTry--); assert( pWal->nSehTry==0 );
+# define SEH_INJECT_FAULT assert( pWal->nSehTry>0 );
+# define SEH_FREE_ON_ERROR(X,Y)
+#endif /* ifdef SQLITE_USE_SEH */
+
+
 /*
 ** Obtain a pointer to the iPage'th page of the wal-index. The wal-index
 ** is broken into pages of WALINDEX_PGSZ bytes. Wal-index pages are
@@ -682,6 +782,7 @@ static int walIndexPage(
   int iPage,               /* The page we seek */
   volatile u32 **ppPage    /* Write the page pointer here */
 ){
+  SEH_INJECT_FAULT;
   if( pWal->nWiData<=iPage || (*ppPage = pWal->apWiData[iPage])==0 ){
     return walIndexPageRealloc(pWal, iPage, ppPage);
   }
@@ -693,6 +794,7 @@ static int walIndexPage(
 */
 static volatile WalCkptInfo *walCkptInfo(Wal *pWal){
   assert( pWal->nWiData>0 && pWal->apWiData[0] );
+  SEH_INJECT_FAULT;
   return (volatile WalCkptInfo*)&(pWal->apWiData[0][sizeof(WalIndexHdr)/2]);
 }
 
@@ -701,6 +803,7 @@ static volatile WalCkptInfo *walCkptInfo(Wal *pWal){
 */
 static volatile WalIndexHdr *walIndexHdr(Wal *pWal){
   assert( pWal->nWiData>0 && pWal->apWiData[0] );
+  SEH_INJECT_FAULT;
   return (volatile WalIndexHdr*)pWal->apWiData[0];
 }
 
@@ -958,12 +1061,18 @@ static int walLockShared(Wal *pWal, int lockIdx){
   WALTRACE(("WAL%p: acquire SHARED-%s %s\n", pWal,
             walLockName(lockIdx), rc ? "failed" : "ok"));
   VVA_ONLY( pWal->lockError = (u8)(rc!=SQLITE_OK && (rc&0xFF)!=SQLITE_BUSY); )
+#ifdef SQLITE_USE_SEH
+  if( rc==SQLITE_OK ) pWal->lockMask |= (1 << lockIdx);
+#endif
   return rc;
 }
 static void walUnlockShared(Wal *pWal, int lockIdx){
   if( pWal->exclusiveMode ) return;
   (void)sqlite3OsShmLock(pWal->pDbFd, lockIdx, 1,
                          SQLITE_SHM_UNLOCK | SQLITE_SHM_SHARED);
+#ifdef SQLITE_USE_SEH
+  pWal->lockMask &= ~(1 << lockIdx);
+#endif
   WALTRACE(("WAL%p: release SHARED-%s\n", pWal, walLockName(lockIdx)));
 }
 static int walLockExclusive(Wal *pWal, int lockIdx, int n){
@@ -974,12 +1083,20 @@ static int walLockExclusive(Wal *pWal, int lockIdx, int n){
   WALTRACE(("WAL%p: acquire EXCLUSIVE-%s cnt=%d %s\n", pWal,
             walLockName(lockIdx), n, rc ? "failed" : "ok"));
   VVA_ONLY( pWal->lockError = (u8)(rc!=SQLITE_OK && (rc&0xFF)!=SQLITE_BUSY); )
+#ifdef SQLITE_USE_SEH
+  if( rc==SQLITE_OK ){
+    pWal->lockMask |= (((1<<n)-1) << (SQLITE_SHM_NLOCK+lockIdx));
+  }
+#endif
   return rc;
 }
 static void walUnlockExclusive(Wal *pWal, int lockIdx, int n){
   if( pWal->exclusiveMode ) return;
   (void)sqlite3OsShmLock(pWal->pDbFd, lockIdx, n,
                          SQLITE_SHM_UNLOCK | SQLITE_SHM_EXCLUSIVE);
+#ifdef SQLITE_USE_SEH
+  pWal->lockMask &= ~(((1<<n)-1) << (SQLITE_SHM_NLOCK+lockIdx));
+#endif
   WALTRACE(("WAL%p: release EXCLUSIVE-%s cnt=%d\n", pWal,
              walLockName(lockIdx), n));
 }
@@ -1071,6 +1188,7 @@ static int walFramePage(u32 iFrame){
 */
 static u32 walFramePgno(Wal *pWal, u32 iFrame){
   int iHash = walFramePage(iFrame);
+  SEH_INJECT_FAULT;
   if( iHash==0 ){
     return pWal->apWiData[0][WALINDEX_HDR_SIZE/sizeof(u32) + iFrame - 1];
   }
@@ -1330,6 +1448,7 @@ static int walIndexRecover(Wal *pWal){
     /* Malloc a buffer to read frames into. */
     szFrame = szPage + WAL_FRAME_HDRSIZE;
     aFrame = (u8 *)sqlite3_malloc64(szFrame + WALINDEX_PGSZ);
+    SEH_FREE_ON_ERROR(0, aFrame);
     if( !aFrame ){
       rc = SQLITE_NOMEM_BKPT;
       goto recovery_error;
@@ -1405,9 +1524,11 @@ static int walIndexRecover(Wal *pWal){
         }
       }
 #endif
+      SEH_INJECT_FAULT;
       if( iFrame<=iLast ) break;
     }
 
+    SEH_FREE_ON_ERROR(aFrame, 0);
     sqlite3_free(aFrame);
   }
 
@@ -1435,6 +1556,7 @@ finished:
         }else{
           pInfo->aReadMark[i] = READMARK_NOT_USED;
         }
+        SEH_INJECT_FAULT;
         walUnlockExclusive(pWal, WAL_READ_LOCK(i), 1);
       }else if( rc!=SQLITE_BUSY ){
         goto recovery_error;
@@ -1827,6 +1949,7 @@ static int walIteratorInit(Wal *pWal, u32 nBackfill, WalIterator **pp){
   memset(p, 0, nByte);
   p->nSegment = nSegment;
   aTmp = (ht_slot*)&(((u8*)p)[nByte]);
+  SEH_FREE_ON_ERROR(0, p);
   for(i=walFramePage(nBackfill+1); rc==SQLITE_OK && i<nSegment; i++){
     WalHashLoc sLoc;
 
@@ -1855,6 +1978,7 @@ static int walIteratorInit(Wal *pWal, u32 nBackfill, WalIterator **pp){
     }
   }
   if( rc!=SQLITE_OK ){
+    SEH_FREE_ON_ERROR(p, 0);
     walIteratorFree(p);
     p = 0;
   }
@@ -2080,13 +2204,13 @@ static int walCheckpoint(
     mxSafeFrame = pWal->hdr.mxFrame;
     mxPage = pWal->hdr.nPage;
     for(i=1; i<WAL_NREADER; i++){
-      u32 y = AtomicLoad(pInfo->aReadMark+i);
+      u32 y = AtomicLoad(pInfo->aReadMark+i); SEH_INJECT_FAULT;
       if( mxSafeFrame>y ){
         assert( y<=pWal->hdr.mxFrame );
         rc = walBusyLock(pWal, xBusy, pBusyArg, WAL_READ_LOCK(i), 1);
         if( rc==SQLITE_OK ){
           u32 iMark = (i==1 ? mxSafeFrame : READMARK_NOT_USED);
-          AtomicStore(pInfo->aReadMark+i, iMark);
+          AtomicStore(pInfo->aReadMark+i, iMark); SEH_INJECT_FAULT;
           walUnlockExclusive(pWal, WAL_READ_LOCK(i), 1);
         }else if( rc==SQLITE_BUSY ){
           mxSafeFrame = y;
@@ -2107,8 +2231,7 @@ static int walCheckpoint(
      && (rc = walBusyLock(pWal,xBusy,pBusyArg,WAL_READ_LOCK(0),1))==SQLITE_OK
     ){
       u32 nBackfill = pInfo->nBackfill;
-
-      pInfo->nBackfillAttempted = mxSafeFrame;
+      pInfo->nBackfillAttempted = mxSafeFrame; SEH_INJECT_FAULT;
 
       /* Sync the WAL to disk */
       rc = sqlite3OsSync(pWal->pWalFd, CKPT_SYNC_FLAGS(sync_flags));
@@ -2139,6 +2262,7 @@ static int walCheckpoint(
       while( rc==SQLITE_OK && 0==walIteratorNext(pIter, &iDbpage, &iFrame) ){
         i64 iOffset;
         assert( walFramePgno(pWal, iFrame)==iDbpage );
+        SEH_INJECT_FAULT;
         if( AtomicLoad(&db->u1.isInterrupted) ){
           rc = db->mallocFailed ? SQLITE_NOMEM_BKPT : SQLITE_INTERRUPT;
           break;
@@ -2168,7 +2292,7 @@ static int walCheckpoint(
           }
         }
         if( rc==SQLITE_OK ){
-          AtomicStore(&pInfo->nBackfill, mxSafeFrame);
+          AtomicStore(&pInfo->nBackfill, mxSafeFrame); SEH_INJECT_FAULT;
         }
       }
 
@@ -2190,6 +2314,7 @@ static int walCheckpoint(
   */
   if( rc==SQLITE_OK && eMode!=SQLITE_CHECKPOINT_PASSIVE ){
     assert( pWal->writeLock );
+    SEH_INJECT_FAULT;
     if( pInfo->nBackfill<pWal->hdr.mxFrame ){
       rc = SQLITE_BUSY;
     }else if( eMode>=SQLITE_CHECKPOINT_RESTART ){
@@ -2221,6 +2346,7 @@ static int walCheckpoint(
   }
 
  walcheckpoint_out:
+  SEH_FREE_ON_ERROR(pIter, 0);
   walIteratorFree(pIter);
   return rc;
 }
@@ -2243,6 +2369,87 @@ static void walLimitSize(Wal *pWal, i64 nMax){
   }
 }
 
+#ifdef SQLITE_USE_SEH
+/*
+** This is the "standard" exception handler used in a few places to handle 
+** an exception thrown by reading from the *-shm mapping after it has become
+** invalid in SQLITE_USE_SEH builds. It is used as follows:
+**
+**   SEH_TRY { ... }
+**   SEH_EXCEPT( rc = walHandleException(pWal); )
+**
+** This function does three things:
+**
+**   1) Determines the locks that should be held, based on the contents of
+**      the Wal.readLock, Wal.writeLock and Wal.ckptLock variables. All other
+**      held locks are assumed to be transient locks that would have been
+**      released had the exception not been thrown and are dropped.
+**
+**   2) Frees the pointer at Wal.pFree, if any, using sqlite3_free().
+**
+**   3) Returns SQLITE_IOERR.
+*/
+static int walHandleException(Wal *pWal){
+  if( pWal->exclusiveMode==0 ){
+    static const int S = 1;
+    static const int E = (1<<SQLITE_SHM_NLOCK);
+    int ii;
+    u32 mUnlock = pWal->lockMask & ~(
+        (pWal->readLock<0 ? 0 : (S << WAL_READ_LOCK(pWal->readLock)))
+        | (pWal->writeLock ? (E << WAL_WRITE_LOCK) : 0)
+        | (pWal->ckptLock ? (E << WAL_CKPT_LOCK) : 0)
+        );
+    for(ii=0; ii<SQLITE_SHM_NLOCK; ii++){
+      if( (S<<ii) & mUnlock ) walUnlockShared(pWal, ii);
+      if( (E<<ii) & mUnlock ) walUnlockExclusive(pWal, ii, 1);
+    }
+  }
+  sqlite3_free(pWal->pFree);
+  pWal->pFree = 0;
+  return SQLITE_IOERR_IN_PAGE;
+}
+
+/*
+** Assert that the Wal.lockMask mask, which indicates the locks held
+** by the connenction, is consistent with the Wal.readLock, Wal.writeLock
+** and Wal.ckptLock variables. To be used as:
+**
+**   assert( walAssertLockmask(pWal) );
+*/
+static int walAssertLockmask(Wal *pWal){
+  if( pWal->exclusiveMode==0 ){
+    static const int S = 1;
+    static const int E = (1<<SQLITE_SHM_NLOCK);
+    u32 mExpect = (
+        (pWal->readLock<0 ? 0 : (S << WAL_READ_LOCK(pWal->readLock)))
+      | (pWal->writeLock ? (E << WAL_WRITE_LOCK) : 0)
+      | (pWal->ckptLock ? (E << WAL_CKPT_LOCK) : 0)
+#ifdef SQLITE_ENABLE_SNAPSHOT
+      | (pWal->pSnapshot ? (pWal->lockMask & (1 << WAL_CKPT_LOCK)) : 0)
+#endif
+    );
+    assert( mExpect==pWal->lockMask );
+  }
+  return 1;
+}
+
+/*
+** Return and zero the "system error" field set when an 
+** EXCEPTION_IN_PAGE_ERROR exception is caught.
+*/
+int sqlite3WalSystemErrno(Wal *pWal){
+  int iRet = 0;
+  if( pWal ){
+    iRet = pWal->iSysErrno;
+    pWal->iSysErrno = 0;
+  }
+  return iRet;
+}
+
+#else
+# define walAssertLockmask(x) 1
+#endif /* ifdef SQLITE_USE_SEH */
+
 /*
 ** Close a connection to a log file.
 */
@@ -2257,6 +2464,8 @@ int sqlite3WalClose(
   if( pWal ){
     int isDelete = 0;             /* True to unlink wal and wal-index files */
 
+    assert( walAssertLockmask(pWal) );
+
     /* If an EXCLUSIVE lock can be obtained on the database file (using the
     ** ordinary, rollback-mode locking methods, this guarantees that the
     ** connection associated with this log file is the only connection to
@@ -2799,6 +3008,7 @@ static int walTryBeginRead(Wal *pWal, int *pChanged, int useWal, int cnt){
   assert( pWal->nWiData>0 );
   assert( pWal->apWiData[0]!=0 );
   pInfo = walCkptInfo(pWal);
+  SEH_INJECT_FAULT;
   if( !useWal && AtomicLoad(&pInfo->nBackfill)==pWal->hdr.mxFrame
 #ifdef SQLITE_ENABLE_SNAPSHOT
    && (pWal->pSnapshot==0 || pWal->hdr.mxFrame==0)
@@ -2848,7 +3058,7 @@ static int walTryBeginRead(Wal *pWal, int *pChanged, int useWal, int cnt){
   }
 #endif
   for(i=1; i<WAL_NREADER; i++){
-    u32 thisMark = AtomicLoad(pInfo->aReadMark+i);
+    u32 thisMark = AtomicLoad(pInfo->aReadMark+i); SEH_INJECT_FAULT;
     if( mxReadMark<=thisMark && thisMark<=mxFrame ){
       assert( thisMark!=READMARK_NOT_USED );
       mxReadMark = thisMark;
@@ -2914,7 +3124,7 @@ static int walTryBeginRead(Wal *pWal, int *pChanged, int useWal, int cnt){
   ** we can guarantee that the checkpointer that set nBackfill could not
   ** see any pages past pWal->hdr.mxFrame, this problem does not come up.
   */
-  pWal->minFrame = AtomicLoad(&pInfo->nBackfill)+1;
+  pWal->minFrame = AtomicLoad(&pInfo->nBackfill)+1; SEH_INJECT_FAULT;
   walShmBarrier(pWal);
   if( AtomicLoad(pInfo->aReadMark+mxI)!=mxReadMark
    || memcmp((void *)walIndexHdr(pWal), &pWal->hdr, sizeof(WalIndexHdr))
@@ -2929,6 +3139,53 @@ static int walTryBeginRead(Wal *pWal, int *pChanged, int useWal, int cnt){
 }
 
 #ifdef SQLITE_ENABLE_SNAPSHOT
+/*
+** This function does the work of sqlite3WalSnapshotRecover().
+*/
+static int walSnapshotRecover(
+  Wal *pWal,                      /* WAL handle */
+  void *pBuf1,                    /* Temp buffer pWal->szPage bytes in size */
+  void *pBuf2                     /* Temp buffer pWal->szPage bytes in size */
+){
+  int szPage = (int)pWal->szPage;
+  int rc;
+  i64 szDb;                       /* Size of db file in bytes */
+
+  rc = sqlite3OsFileSize(pWal->pDbFd, &szDb);
+  if( rc==SQLITE_OK ){
+    volatile WalCkptInfo *pInfo = walCkptInfo(pWal);
+    u32 i = pInfo->nBackfillAttempted;
+    for(i=pInfo->nBackfillAttempted; i>AtomicLoad(&pInfo->nBackfill); i--){
+      WalHashLoc sLoc;          /* Hash table location */
+      u32 pgno;                 /* Page number in db file */
+      i64 iDbOff;               /* Offset of db file entry */
+      i64 iWalOff;              /* Offset of wal file entry */
+
+      rc = walHashGet(pWal, walFramePage(i), &sLoc);
+      if( rc!=SQLITE_OK ) break;
+      pgno = sLoc.aPgno[i-sLoc.iZero];
+      iDbOff = (i64)(pgno-1) * szPage;
+
+      if( iDbOff+szPage<=szDb ){
+        iWalOff = walFrameOffset(i, szPage) + WAL_FRAME_HDRSIZE;
+        rc = sqlite3OsRead(pWal->pWalFd, pBuf1, szPage, iWalOff);
+
+        if( rc==SQLITE_OK ){
+          rc = sqlite3OsRead(pWal->pDbFd, pBuf2, szPage, iDbOff);
+        }
+
+        if( rc!=SQLITE_OK || 0==memcmp(pBuf1, pBuf2, szPage) ){
+          break;
+        }
+      }
+
+      pInfo->nBackfillAttempted = i-1;
+    }
+  }
+
+  return rc;
+}
+
 /*
 ** Attempt to reduce the value of the WalCkptInfo.nBackfillAttempted
 ** variable so that older snapshots can be accessed. To do this, loop
@@ -2954,50 +3211,21 @@ int sqlite3WalSnapshotRecover(Wal *pWal){
   assert( pWal->readLock>=0 );
   rc = walLockExclusive(pWal, WAL_CKPT_LOCK, 1);
   if( rc==SQLITE_OK ){
-    volatile WalCkptInfo *pInfo = walCkptInfo(pWal);
-    int szPage = (int)pWal->szPage;
-    i64 szDb;                   /* Size of db file in bytes */
-
-    rc = sqlite3OsFileSize(pWal->pDbFd, &szDb);
-    if( rc==SQLITE_OK ){
-      void *pBuf1 = sqlite3_malloc(szPage);
-      void *pBuf2 = sqlite3_malloc(szPage);
-      if( pBuf1==0 || pBuf2==0 ){
-        rc = SQLITE_NOMEM;
-      }else{
-        u32 i = pInfo->nBackfillAttempted;
-        for(i=pInfo->nBackfillAttempted; i>AtomicLoad(&pInfo->nBackfill); i--){
-          WalHashLoc sLoc;          /* Hash table location */
-          u32 pgno;                 /* Page number in db file */
-          i64 iDbOff;               /* Offset of db file entry */
-          i64 iWalOff;              /* Offset of wal file entry */
-
-          rc = walHashGet(pWal, walFramePage(i), &sLoc);
-          if( rc!=SQLITE_OK ) break;
-          assert( i - sLoc.iZero - 1 >=0 );
-          pgno = sLoc.aPgno[i-sLoc.iZero-1];
-          iDbOff = (i64)(pgno-1) * szPage;
-
-          if( iDbOff+szPage<=szDb ){
-            iWalOff = walFrameOffset(i, szPage) + WAL_FRAME_HDRSIZE;
-            rc = sqlite3OsRead(pWal->pWalFd, pBuf1, szPage, iWalOff);
-
-            if( rc==SQLITE_OK ){
-              rc = sqlite3OsRead(pWal->pDbFd, pBuf2, szPage, iDbOff);
-            }
-
-            if( rc!=SQLITE_OK || 0==memcmp(pBuf1, pBuf2, szPage) ){
-              break;
-            }
-          }
-
-          pInfo->nBackfillAttempted = i-1;
-        }
+    void *pBuf1 = sqlite3_malloc(pWal->szPage);
+    void *pBuf2 = sqlite3_malloc(pWal->szPage);
+    if( pBuf1==0 || pBuf2==0 ){
+      rc = SQLITE_NOMEM;
+    }else{
+      pWal->ckptLock = 1;
+      SEH_TRY {
+        rc = walSnapshotRecover(pWal, pBuf1, pBuf2);
       }
-
-      sqlite3_free(pBuf1);
-      sqlite3_free(pBuf2);
+      SEH_EXCEPT( rc = SQLITE_IOERR_IN_PAGE; )
+      pWal->ckptLock = 0;
     }
+
+    sqlite3_free(pBuf1);
+    sqlite3_free(pBuf2);
     walUnlockExclusive(pWal, WAL_CKPT_LOCK, 1);
   }
 
@@ -3006,28 +3234,20 @@ int sqlite3WalSnapshotRecover(Wal *pWal){
 #endif /* SQLITE_ENABLE_SNAPSHOT */
 
 /*
-** Begin a read transaction on the database.
-**
-** This routine used to be called sqlite3OpenSnapshot() and with good reason:
-** it takes a snapshot of the state of the WAL and wal-index for the current
-** instant in time.  The current thread will continue to use this snapshot.
-** Other threads might append new content to the WAL and wal-index but
-** that extra content is ignored by the current thread.
-**
-** If the database contents have changes since the previous read
-** transaction, then *pChanged is set to 1 before returning.  The
-** Pager layer will use this to know that its cache is stale and
-** needs to be flushed.
+** This function does the work of sqlite3WalBeginReadTransaction() (see 
+** below). That function simply calls this one inside an SEH_TRY{...} block.
 */
-int sqlite3WalBeginReadTransaction(Wal *pWal, int *pChanged){
+static int walBeginReadTransaction(Wal *pWal, int *pChanged){
   int rc;                         /* Return code */
   int cnt = 0;                    /* Number of TryBeginRead attempts */
 #ifdef SQLITE_ENABLE_SNAPSHOT
+  int ckptLock = 0;
   int bChanged = 0;
   WalIndexHdr *pSnapshot = pWal->pSnapshot;
 #endif
 
   assert( pWal->ckptLock==0 );
+  assert( pWal->nSehTry>0 );
 
 #ifdef SQLITE_ENABLE_SNAPSHOT
   if( pSnapshot ){
@@ -3050,7 +3270,7 @@ int sqlite3WalBeginReadTransaction(Wal *pWal, int *pChanged){
     if( rc!=SQLITE_OK ){
       return rc;
     }
-    pWal->ckptLock = 1;
+    ckptLock = 1;
   }
 #endif
 
@@ -3114,15 +3334,37 @@ int sqlite3WalBeginReadTransaction(Wal *pWal, int *pChanged){
   }
 
   /* Release the shared CKPT lock obtained above. */
-  if( pWal->ckptLock ){
+  if( ckptLock ){
     assert( pSnapshot );
     walUnlockShared(pWal, WAL_CKPT_LOCK);
-    pWal->ckptLock = 0;
   }
 #endif
   return rc;
 }
 
+/*
+** Begin a read transaction on the database.
+**
+** This routine used to be called sqlite3OpenSnapshot() and with good reason:
+** it takes a snapshot of the state of the WAL and wal-index for the current
+** instant in time.  The current thread will continue to use this snapshot.
+** Other threads might append new content to the WAL and wal-index but
+** that extra content is ignored by the current thread.
+**
+** If the database contents have changes since the previous read
+** transaction, then *pChanged is set to 1 before returning.  The
+** Pager layer will use this to know that its cache is stale and
+** needs to be flushed.
+*/
+int sqlite3WalBeginReadTransaction(Wal *pWal, int *pChanged){
+  int rc;
+  SEH_TRY {
+    rc = walBeginReadTransaction(pWal, pChanged);
+  }
+  SEH_EXCEPT( rc = walHandleException(pWal); )
+  return rc;
+}
+
 /*
 ** Finish with a read transaction.  All this does is release the
 ** read-lock.
@@ -3143,7 +3385,7 @@ void sqlite3WalEndReadTransaction(Wal *pWal){
 ** Return SQLITE_OK if successful, or an error code if an error occurs. If an
 ** error does occur, the final value of *piRead is undefined.
 */
-int sqlite3WalFindFrame(
+static int walFindFrame(
   Wal *pWal,                      /* WAL handle */
   Pgno pgno,                      /* Database page number to read data for */
   u32 *piRead                     /* OUT: Frame number (or zero) */
@@ -3206,6 +3448,7 @@ int sqlite3WalFindFrame(
     }
     nCollide = HASHTABLE_NSLOT;
     iKey = walHash(pgno);
+    SEH_INJECT_FAULT;
     while( (iH = AtomicLoad(&sLoc.aHash[iKey]))!=0 ){
       u32 iFrame = iH + sLoc.iZero;
       if( iFrame<=iLast && iFrame>=pWal->minFrame && sLoc.aPgno[iH-1]==pgno ){
@@ -3242,6 +3485,30 @@ int sqlite3WalFindFrame(
   return SQLITE_OK;
 }
 
+/*
+** Search the wal file for page pgno. If found, set *piRead to the frame that
+** contains the page. Otherwise, if pgno is not in the wal file, set *piRead
+** to zero.
+**
+** Return SQLITE_OK if successful, or an error code if an error occurs. If an
+** error does occur, the final value of *piRead is undefined.
+**
+** The difference between this function and walFindFrame() is that this
+** function wraps walFindFrame() in an SEH_TRY{...} block.
+*/
+int sqlite3WalFindFrame(
+  Wal *pWal,                      /* WAL handle */
+  Pgno pgno,                      /* Database page number to read data for */
+  u32 *piRead                     /* OUT: Frame number (or zero) */
+){
+  int rc;
+  SEH_TRY {
+    rc = walFindFrame(pWal, pgno, piRead);
+  }
+  SEH_EXCEPT( rc = SQLITE_IOERR_IN_PAGE; )
+  return rc;
+}
+
 /*
 ** Read the contents of frame iRead from the wal file into buffer pOut
 ** (which is nOut bytes in size). Return SQLITE_OK if successful, or an
@@ -3323,12 +3590,17 @@ int sqlite3WalBeginWriteTransaction(Wal *pWal){
   ** time the read transaction on this connection was started, then
   ** the write is disallowed.
   */
-  if( memcmp(&pWal->hdr, (void *)walIndexHdr(pWal), sizeof(WalIndexHdr))!=0 ){
+  SEH_TRY {
+    if( memcmp(&pWal->hdr, (void *)walIndexHdr(pWal), sizeof(WalIndexHdr))!=0 ){
+      rc = SQLITE_BUSY_SNAPSHOT;
+    }
+  }
+  SEH_EXCEPT( rc = SQLITE_IOERR_IN_PAGE; )
+
+  if( rc!=SQLITE_OK ){
     walUnlockExclusive(pWal, WAL_WRITE_LOCK, 1);
     pWal->writeLock = 0;
-    rc = SQLITE_BUSY_SNAPSHOT;
   }
-
   return rc;
 }
 
@@ -3364,30 +3636,33 @@ int sqlite3WalUndo(Wal *pWal, int (*xUndo)(void *, Pgno), void *pUndoCtx){
     Pgno iMax = pWal->hdr.mxFrame;
     Pgno iFrame;
 
-    /* Restore the clients cache of the wal-index header to the state it
-    ** was in before the client began writing to the database.
-    */
-    memcpy(&pWal->hdr, (void *)walIndexHdr(pWal), sizeof(WalIndexHdr));
-
-    for(iFrame=pWal->hdr.mxFrame+1;
-        ALWAYS(rc==SQLITE_OK) && iFrame<=iMax;
-        iFrame++
-    ){
-      /* This call cannot fail. Unless the page for which the page number
-      ** is passed as the second argument is (a) in the cache and
-      ** (b) has an outstanding reference, then xUndo is either a no-op
-      ** (if (a) is false) or simply expels the page from the cache (if (b)
-      ** is false).
-      **
-      ** If the upper layer is doing a rollback, it is guaranteed that there
-      ** are no outstanding references to any page other than page 1. And
-      ** page 1 is never written to the log until the transaction is
-      ** committed. As a result, the call to xUndo may not fail.
+    SEH_TRY {
+      /* Restore the clients cache of the wal-index header to the state it
+      ** was in before the client began writing to the database. 
       */
-      assert( walFramePgno(pWal, iFrame)!=1 );
-      rc = xUndo(pUndoCtx, walFramePgno(pWal, iFrame));
+      memcpy(&pWal->hdr, (void *)walIndexHdr(pWal), sizeof(WalIndexHdr));
+  
+      for(iFrame=pWal->hdr.mxFrame+1; 
+          ALWAYS(rc==SQLITE_OK) && iFrame<=iMax; 
+          iFrame++
+      ){
+        /* This call cannot fail. Unless the page for which the page number
+        ** is passed as the second argument is (a) in the cache and
+        ** (b) has an outstanding reference, then xUndo is either a no-op
+        ** (if (a) is false) or simply expels the page from the cache (if (b)
+        ** is false).
+        **
+        ** If the upper layer is doing a rollback, it is guaranteed that there
+        ** are no outstanding references to any page other than page 1. And
+        ** page 1 is never written to the log until the transaction is
+        ** committed. As a result, the call to xUndo may not fail.
+        */
+        assert( walFramePgno(pWal, iFrame)!=1 );
+        rc = xUndo(pUndoCtx, walFramePgno(pWal, iFrame));
+      }
+      if( iMax!=pWal->hdr.mxFrame ) walCleanupHash(pWal);
     }
-    if( iMax!=pWal->hdr.mxFrame ) walCleanupHash(pWal);
+    SEH_EXCEPT( rc = SQLITE_IOERR_IN_PAGE; )
   }
   return rc;
 }
@@ -3431,7 +3706,10 @@ int sqlite3WalSavepointUndo(Wal *pWal, u32 *aWalData){
     pWal->hdr.mxFrame = aWalData[0];
     pWal->hdr.aFrameCksum[0] = aWalData[1];
     pWal->hdr.aFrameCksum[1] = aWalData[2];
-    walCleanupHash(pWal);
+    SEH_TRY {
+      walCleanupHash(pWal);
+    }
+    SEH_EXCEPT( rc = SQLITE_IOERR_IN_PAGE; )
   }
 
   return rc;
@@ -3612,7 +3890,7 @@ static int walRewriteChecksums(Wal *pWal, u32 iLast){
 ** Write a set of frames to the log. The caller must hold the write-lock
 ** on the log file (obtained using sqlite3WalBeginWriteTransaction()).
 */
-int sqlite3WalFrames(
+static int walFrames(
   Wal *pWal,                      /* Wal handle to write to */
   int szPage,                     /* Database page-size in bytes */
   PgHdr *pList,                   /* List of dirty pages to write */
@@ -3723,7 +4001,7 @@ int sqlite3WalFrames(
     ** checksums must be recomputed when the transaction is committed.  */
     if( iFirst && (p->pDirty || isCommit==0) ){
       u32 iWrite = 0;
-      VVA_ONLY(rc =) sqlite3WalFindFrame(pWal, p->pgno, &iWrite);
+      VVA_ONLY(rc =) walFindFrame(pWal, p->pgno, &iWrite);
       assert( rc==SQLITE_OK || iWrite==0 );
       if( iWrite>=iFirst ){
         i64 iOff = walFrameOffset(iWrite, szPage) + WAL_FRAME_HDRSIZE;
@@ -3842,6 +4120,29 @@ int sqlite3WalFrames(
   return rc;
 }
 
+/* 
+** Write a set of frames to the log. The caller must hold the write-lock
+** on the log file (obtained using sqlite3WalBeginWriteTransaction()).
+**
+** The difference between this function and walFrames() is that this
+** function wraps walFrames() in an SEH_TRY{...} block.
+*/
+int sqlite3WalFrames(
+  Wal *pWal,                      /* Wal handle to write to */
+  int szPage,                     /* Database page-size in bytes */
+  PgHdr *pList,                   /* List of dirty pages to write */
+  Pgno nTruncate,                 /* Database size after this commit */
+  int isCommit,                   /* True if this is a commit */
+  int sync_flags                  /* Flags to pass to OsSync() (or 0) */
+){
+  int rc;
+  SEH_TRY {
+    rc = walFrames(pWal, szPage, pList, nTruncate, isCommit, sync_flags);
+  }
+  SEH_EXCEPT( rc = walHandleException(pWal); )
+  return rc;
+}
+
 /*
 ** This routine is called to implement sqlite3_wal_checkpoint() and
 ** related interfaces.
@@ -3921,30 +4222,33 @@ int sqlite3WalCheckpoint(
 
 
   /* Read the wal-index header. */
-  if( rc==SQLITE_OK ){
-    walDisableBlocking(pWal);
-    rc = walIndexReadHdr(pWal, &isChanged);
-    (void)walEnableBlocking(pWal);
-    if( isChanged && pWal->pDbFd->pMethods->iVersion>=3 ){
-      sqlite3OsUnfetch(pWal->pDbFd, 0, 0);
-    }
-  }
-
-  /* Copy data from the log to the database file. */
-  if( rc==SQLITE_OK ){
-
-    if( pWal->hdr.mxFrame && walPagesize(pWal)!=nBuf ){
-      rc = SQLITE_CORRUPT_BKPT;
-    }else{
-      rc = walCheckpoint(pWal, db, eMode2, xBusy2, pBusyArg, sync_flags, zBuf);
-    }
-
-    /* If no error occurred, set the output variables. */
-    if( rc==SQLITE_OK || rc==SQLITE_BUSY ){
-      if( pnLog ) *pnLog = (int)pWal->hdr.mxFrame;
-      if( pnCkpt ) *pnCkpt = (int)(walCkptInfo(pWal)->nBackfill);
+  SEH_TRY {
+    if( rc==SQLITE_OK ){
+      walDisableBlocking(pWal);
+      rc = walIndexReadHdr(pWal, &isChanged);
+      (void)walEnableBlocking(pWal);
+      if( isChanged && pWal->pDbFd->pMethods->iVersion>=3 ){
+        sqlite3OsUnfetch(pWal->pDbFd, 0, 0);
+      }
+    }
+  
+    /* Copy data from the log to the database file. */
+    if( rc==SQLITE_OK ){
+      if( pWal->hdr.mxFrame && walPagesize(pWal)!=nBuf ){
+        rc = SQLITE_CORRUPT_BKPT;
+      }else{
+        rc = walCheckpoint(pWal, db, eMode2, xBusy2, pBusyArg, sync_flags,zBuf);
+      }
+
+      /* If no error occurred, set the output variables. */
+      if( rc==SQLITE_OK || rc==SQLITE_BUSY ){
+        if( pnLog ) *pnLog = (int)pWal->hdr.mxFrame;
+        SEH_INJECT_FAULT;
+        if( pnCkpt ) *pnCkpt = (int)(walCkptInfo(pWal)->nBackfill);
+      }
     }
   }
+  SEH_EXCEPT( rc = walHandleException(pWal); )
 
   if( isChanged ){
     /* If a new wal-index header was loaded before the checkpoint was
@@ -4021,7 +4325,9 @@ int sqlite3WalExclusiveMode(Wal *pWal, int op){
   ** locks are taken in this case). Nor should the pager attempt to
   ** upgrade to exclusive-mode following such an error.
   */
+#ifndef SQLITE_USE_SEH
   assert( pWal->readLock>=0 || pWal->lockError );
+#endif
   assert( pWal->readLock>=0 || (op<=0 && pWal->exclusiveMode==0) );
 
   if( op==0 ){
@@ -4122,16 +4428,19 @@ int sqlite3_snapshot_cmp(sqlite3_snapshot *p1, sqlite3_snapshot *p2){
 */
 int sqlite3WalSnapshotCheck(Wal *pWal, sqlite3_snapshot *pSnapshot){
   int rc;
-  rc = walLockShared(pWal, WAL_CKPT_LOCK);
-  if( rc==SQLITE_OK ){
-    WalIndexHdr *pNew = (WalIndexHdr*)pSnapshot;
-    if( memcmp(pNew->aSalt, pWal->hdr.aSalt, sizeof(pWal->hdr.aSalt))
-     || pNew->mxFrame<walCkptInfo(pWal)->nBackfillAttempted
-    ){
-      rc = SQLITE_ERROR_SNAPSHOT;
-      walUnlockShared(pWal, WAL_CKPT_LOCK);
+  SEH_TRY {
+    rc = walLockShared(pWal, WAL_CKPT_LOCK);
+    if( rc==SQLITE_OK ){
+      WalIndexHdr *pNew = (WalIndexHdr*)pSnapshot;
+      if( memcmp(pNew->aSalt, pWal->hdr.aSalt, sizeof(pWal->hdr.aSalt))
+       || pNew->mxFrame<walCkptInfo(pWal)->nBackfillAttempted
+      ){
+        rc = SQLITE_ERROR_SNAPSHOT;
+        walUnlockShared(pWal, WAL_CKPT_LOCK);
+      }
     }
   }
+  SEH_EXCEPT( rc = walHandleException(pWal); )
   return rc;
 }
 
diff --git a/src/wal.h b/src/wal.h
index 02e2bab360..d39bb50f3d 100644
--- a/src/wal.h
+++ b/src/wal.h
@@ -151,5 +151,9 @@ int sqlite3WalWriteLock(Wal *pWal, int bLock);
 void sqlite3WalDb(Wal *pWal, sqlite3 *db);
 #endif
 
+#ifdef SQLITE_USE_SEH
+int sqlite3WalSystemErrno(Wal*);
+#endif
+
 #endif /* ifndef SQLITE_OMIT_WAL */
 #endif /* SQLITE_WAL_H */
diff --git a/test/json101.test b/test/json101.test
index 543e4c71e7..8bb133ec73 100644
--- a/test/json101.test
+++ b/test/json101.test
@@ -923,9 +923,15 @@ do_execsql_test json-20.3 {
 # a NULL value as the JSON input.
 #
 db null NULL
-do_execsql_test json-21.1 {
-  SELECT json_valid(NULL);
-} NULL
+if {[db exists {SELECT * FROM pragma_compile_options WHERE compile_options LIKE '%legacy_json_valid%'}]} {
+  do_execsql_test json-21.1-legacy {
+    SELECT json_valid(NULL);
+  } 0
+} else {
+  do_execsql_test json-21.1-correct {
+    SELECT json_valid(NULL);
+  } NULL
+}
 do_execsql_test json-21.2 {
   SELECT json_error_position(NULL);
 } NULL
diff --git a/test/snapshot_fault.test b/test/snapshot_fault.test
index 2adb793650..10c5094594 100644
--- a/test/snapshot_fault.test
+++ b/test/snapshot_fault.test
@@ -23,6 +23,7 @@ set testprefix snapshot_fault
 # checkpointing the db.
 #
 do_faultsim_test 1.0 -prep {
+  catch { db2 close }
   faultsim_delete_and_reopen
   sqlite3 db2 test.db
   db2 eval { 
diff --git a/test/walseh1.test b/test/walseh1.test
new file mode 100644
index 0000000000..c3a655f534
--- /dev/null
+++ b/test/walseh1.test
@@ -0,0 +1,150 @@
+# 2021 August 16
+#
+# The author disclaims copyright to this source code.  In place of
+# a legal notice, here is a blessing:
+#
+#    May you do good and not evil.
+#    May you find forgiveness for yourself and forgive others.
+#    May you share freely, never taking more than you give.
+#
+#***********************************************************************
+#
+
+set testdir [file dirname $argv0]
+source $testdir/tester.tcl
+source $testdir/malloc_common.tcl
+set testprefix walseh1
+
+set ::seh_countdown 0 
+set ::seh_errno 10
+proc seh_faultsim_callback {iFault} {
+  if {$iFault==650} {
+    incr ::seh_countdown -1
+    if {$::seh_countdown==0} { return $::seh_errno }
+  }
+  return 0
+}
+
+proc seh_injectinstall {} {
+  sqlite3_test_control_fault_install seh_faultsim_callback
+}
+proc seh_injectuninstall {} {
+  sqlite3_test_control_fault_install
+}
+proc seh_injectstart {iFail} {
+  set ::seh_errno [expr 2+$iFail*10]
+  set ::seh_countdown $iFail
+}
+proc seh_injectstop {} {
+  set res [expr $::seh_countdown<=0]
+  set ::seh_countdown 0
+  set res
+}
+
+set FAULTSIM(seh) [list                   \
+  -injectinstall   seh_injectinstall   \
+  -injectstart     seh_injectstart     \
+  -injectstop      seh_injectstop      \
+  -injecterrlist   {{1 {disk I/O error}}} \
+  -injectuninstall seh_injectuninstall \
+]
+
+proc test_system_errno {db expect} {
+  set serrno [sqlite3_system_errno $db]
+  if {$serrno!=$expect} {
+    error "surprising system_errno. Expected $expect, got $serrno"
+  }  
+}
+
+do_execsql_test 1.0 {
+  PRAGMA journal_mode = wal;
+  CREATE TABLE t1(x, y);
+  INSERT INTO t1 VALUES(1, 2);
+  INSERT INTO t1 VALUES(3, 4);
+} {wal}
+faultsim_save_and_close
+
+do_faultsim_test 1 -faults seh -prep {
+  catch { db2 close }
+  faultsim_restore_and_reopen
+  execsql { SELECT * FROM sqlite_schema } 
+  sqlite3 db2 test.db
+} -body {
+  execsql { SELECT * FROM t1 } db2
+} -test {
+  faultsim_test_result {0 {1 2 3 4}} 
+  if {$testrc} { test_system_errno db2 $::seh_errno }
+}
+catch { db2 close }
+
+faultsim_save_and_close
+
+do_faultsim_test 2 -faults seh -prep {
+  catch { db close }
+  faultsim_restore_and_reopen
+} -body {
+  execsql { SELECT * FROM t1 } 
+} -test {
+  faultsim_test_result {0 {1 2 3 4}} 
+  if {$testrc} { test_system_errno db $::seh_errno }
+}
+
+do_faultsim_test 3 -faults seh -prep {
+  catch { db close }
+  faultsim_restore_and_reopen
+} -body {
+  execsql { INSERT INTO t1 VALUES(5, 6) }
+  execsql { SELECT * FROM t1 }
+} -test {
+  faultsim_test_result {0 {1 2 3 4 5 6}} 
+  if {$testrc} { test_system_errno db $::seh_errno }
+}
+
+do_faultsim_test 4 -faults seh -prep {
+  catch { db close }
+  faultsim_restore_and_reopen
+} -body {
+  execsql { PRAGMA wal_checkpoint }
+  execsql { INSERT INTO t1 VALUES(7, 8) }
+  execsql { SELECT * FROM t1 }
+} -test {
+  faultsim_test_result {0 {1 2 3 4 7 8}} 
+  if {$testrc} { test_system_errno db $::seh_errno }
+}
+catch { db close }
+
+do_faultsim_test 5 -faults seh -prep {
+  catch { db close }
+  faultsim_restore_and_reopen
+  execsql {
+    PRAGMA cache_size = 5;
+    BEGIN;
+      WITH s(i) AS (
+        SELECT 1 UNION ALL SELECT i+1 FROM s WHERE i<50
+      )
+      INSERT INTO t1 SELECT randomblob(500), randomblob(500) FROM s;
+  }
+} -body {
+  execsql ROLLBACK
+} -test {
+  faultsim_test_result {0 {}}
+  if {$testrc} { test_system_errno db $::seh_errno }
+}
+catch { db close }
+
+do_faultsim_test 6 -faults seh -prep {
+  catch { db close }
+  faultsim_restore_and_reopen
+} -body {
+  execsql { PRAGMA wal_checkpoint = TRUNCATE }
+  execsql { INSERT INTO t1 VALUES(7, 8) }
+  execsql { SELECT * FROM t1 }
+} -test {
+  faultsim_test_result {0 {1 2 3 4 7 8}} 
+  if {$testrc} { test_system_errno db $::seh_errno }
+}
+catch { db close }
+
+finish_test
+
+
diff --git a/tool/mkctimec.tcl b/tool/mkctimec.tcl
index bcb1a54bb8..317f30a35f 100755
--- a/tool/mkctimec.tcl
+++ b/tool/mkctimec.tcl
@@ -180,6 +180,7 @@ set boolean_defnil_options {
   SQLITE_IGNORE_FLOCK_LOCK_ERRORS
   SQLITE_INLINE_MEMCPY
   SQLITE_INT64_TYPE
+  SQLITE_LEGACY_JSON_VALID
   SQLITE_LIKE_DOESNT_MATCH_BLOBS
   SQLITE_LOCK_TRACE
   SQLITE_LOG_CACHE_SPILL