Add an experimental fix to avoid attempting to mmap memory from an offset that is not a multiple of the system page size on systems with page sizes larger than 32KB.

FossilOrigin-Name: 6f3a5c24d254fc6faf607b505bdef4a7aafc21af

manifest

@@ -1,5 +1,5 @@
-C Avoid\ssome\sunnecessary\scalls\sto\ssqlite3VdbeRecordUnpack()\sthat\swere\sbeing\smade\swhen\smerging\sdata\sfrom\stwo\sor\smore\stemp\sfiles\stogether\sin\svdbesort.c
+C Add\san\sexperimental\sfix\sto\savoid\sattempting\sto\smmap\smemory\sfrom\san\soffset\sthat\sis\snot\sa\smultiple\sof\sthe\ssystem\spage\ssize\son\ssystems\swith\spage\ssizes\slarger\sthan\s32KB.
-D 2014-03-19T20:01:25.712
+D 2014-03-20T08:59:47.455
 F Makefile.arm-wince-mingw32ce-gcc d6df77f1f48d690bd73162294bbba7f59507c72f
 F Makefile.in 2ef13430cd359f7b361bb863504e227b25cc7f81
 F Makefile.linux-gcc 91d710bdc4998cb015f39edf3cb314ec4f4d7e23
@@ -203,7 +203,7 @@ F src/notify.c 976dd0f6171d4588e89e874fcc765e92914b6d30
 F src/os.c 1b147e4cf7cc39e618115c14a086aed44bc91ace
 F src/os.h 4a46270a64e9193af4a0aaa3bc2c66dc07c29b3f
 F src/os_common.h 92815ed65f805560b66166e3583470ff94478f04
-F src/os_unix.c 18f7f95dc6bcb9cf4d4a238d8e2de96611bc2ae5
+F src/os_unix.c 7e2f6348e99bd215d36cb5d40161b06456089e21
 F src/os_win.c e71678ac927d0a0fb11d993db20a9748eabf808e
 F src/pager.c 97a8908bf4e6e7c3adea09d3597cfa48ae33ab4e
 F src/pager.h ffd5607f7b3e4590b415b007a4382f693334d428
@@ -1156,7 +1156,10 @@ F tool/vdbe_profile.tcl 67746953071a9f8f2f668b73fe899074e2c6d8c1
 F tool/warnings-clang.sh f6aa929dc20ef1f856af04a730772f59283631d4
 F tool/warnings.sh d1a6de74685f360ab718efda6265994b99bbea01
 F tool/win/sqlite.vsix 030f3eeaf2cb811a3692ab9c14d021a75ce41fff
-P ecd9d3f9453be0bb8e312d8027fd1a9e55882f36
+P 707ea170b3e26965b7e3982f7554d122d130b9a6
-R 597feeb3c9b32d5be1e5c696f1b077da
+R df2b4ee35d794d54be353b7886f4773f
+T *branch * shm-mapping-fix
+T *sym-shm-mapping-fix *
+T -sym-trunk *
 U dan
-Z 03e3772c0627172d43f05f231b29ede3
+Z 8f1167a615e2deebf3a41d21381f8bfc

manifest.uuid

@@ -1 +1 @@
-707ea170b3e26965b7e3982f7554d122d130b9a6
+6f3a5c24d254fc6faf607b505bdef4a7aafc21af

src/os_unix.c

@@ -4105,6 +4105,33 @@ static int unixShmSystemLock(
   return rc;        
 }
 
+/*
+** Return the system page size.
+*/
+static int unixGetPagesize(void){
+#if defined(_BSD_SOURCE)
+  return getpagesize();
+#else
+  return (int)sysconf(_SC_PAGESIZE);
+#endif
+}
+
+/*
+** Return the minimum number of 32KB shm regions that should be mapped at
+** a time, assuming that each mapping must be an integer multiple of the
+** current system page-size.
+**
+** Usually, this is 1. The exception seems to be systems that are configured
+** to use 64KB pages - in this case each mapping must cover at least two
+** shm regions.
+*/
+static int unixShmRegionPerMap(void){
+  int shmsz = 32*1024;            /* SHM region size */
+  int pgsz = unixGetPagesize();   /* System page size */
+  assert( ((pgsz-1)&pgsz)==0 );   /* Page size must be a power of 2 */
+  if( pgsz<shmsz ) return 1;
+  return pgsz/shmsz;
+}
 
 /*
 ** Purge the unixShmNodeList list of all entries with unixShmNode.nRef==0.
@@ -4116,10 +4143,11 @@ static void unixShmPurge(unixFile *pFd){
   unixShmNode *p = pFd->pInode->pShmNode;
   assert( unixMutexHeld() );
   if( p && p->nRef==0 ){
+    int nShmPerMap = unixShmRegionPerMap();
     int i;
     assert( p->pInode==pFd->pInode );
     sqlite3_mutex_free(p->mutex);
-    for(i=0; i<p->nRegion; i++){
+    for(i=0; i<p->nRegion; i+=nShmPerMap){
       if( p->h>=0 ){
         osMunmap(p->apRegion[i], p->szRegion);
       }else{
@@ -4326,6 +4354,8 @@ static int unixShmMap(
   unixShm *p;
   unixShmNode *pShmNode;
   int rc = SQLITE_OK;
+  int nShmPerMap = unixShmRegionPerMap();
+  int nReqRegion;
 
   /* If the shared-memory file has not yet been opened, open it now. */
   if( pDbFd->pShm==0 ){
@@ -4341,9 +4371,12 @@ static int unixShmMap(
   assert( pShmNode->h>=0 || pDbFd->pInode->bProcessLock==1 );
   assert( pShmNode->h<0 || pDbFd->pInode->bProcessLock==0 );
 
-  if( pShmNode->nRegion<=iRegion ){
+  /* Minimum number of regions required to be mapped. */
+  nReqRegion = ((iRegion+nShmPerMap) / nShmPerMap) * nShmPerMap;
+
+  if( pShmNode->nRegion<nReqRegion ){
     char **apNew;                      /* New apRegion[] array */
-    int nByte = (iRegion+1)*szRegion;  /* Minimum required file size */
+    int nByte = nReqRegion*szRegion;   /* Minimum required file size */
     struct stat sStat;                 /* Used by fstat() */
 
     pShmNode->szRegion = szRegion;
@@ -4392,17 +4425,19 @@ static int unixShmMap(
 
     /* Map the requested memory region into this processes address space. */
     apNew = (char **)sqlite3_realloc(
-        pShmNode->apRegion, (iRegion+1)*sizeof(char *)
+        pShmNode->apRegion, nReqRegion*sizeof(char *)
     );
     if( !apNew ){
       rc = SQLITE_IOERR_NOMEM;
       goto shmpage_out;
     }
     pShmNode->apRegion = apNew;
-    while(pShmNode->nRegion<=iRegion){
+    while( pShmNode->nRegion<nReqRegion ){
+      int nMap = szRegion*nShmPerMap;
+      int i;
       void *pMem;
       if( pShmNode->h>=0 ){
-        pMem = osMmap(0, szRegion,
+        pMem = osMmap(0, nMap,
             pShmNode->isReadonly ? PROT_READ : PROT_READ|PROT_WRITE, 
             MAP_SHARED, pShmNode->h, szRegion*(i64)pShmNode->nRegion
         );
@@ -4418,8 +4453,11 @@ static int unixShmMap(
         }
         memset(pMem, 0, szRegion);
       }
-      pShmNode->apRegion[pShmNode->nRegion] = pMem;
+
-      pShmNode->nRegion++;
+      for(i=0; i<nShmPerMap; i++){
+        pShmNode->apRegion[pShmNode->nRegion+i] = &((char*)pMem)[szRegion*i];
+      }
+      pShmNode->nRegion += nShmPerMap;
     }
   }
 
@@ -4633,19 +4671,6 @@ static void unixUnmapfile(unixFile *pFd){
   }
 }
 
-/*
-** Return the system page size.
-*/
-static int unixGetPagesize(void){
-#if HAVE_MREMAP
-  return 512;
-#elif defined(_BSD_SOURCE)
-  return getpagesize();
-#else
-  return (int)sysconf(_SC_PAGESIZE);
-#endif
-}
-
 /*
 ** Attempt to set the size of the memory mapping maintained by file 
 ** descriptor pFd to nNew bytes. Any existing mapping is discarded.
@@ -4682,8 +4707,12 @@ static void unixRemapfile(
   if( (pFd->ctrlFlags & UNIXFILE_RDONLY)==0 ) flags |= PROT_WRITE;
 
   if( pOrig ){
+#if HAVE_MREMAP
+    i64 nReuse = pFd->mmapSize;
+#else
     const int szSyspage = unixGetPagesize();
     i64 nReuse = (pFd->mmapSize & ~(szSyspage-1));
+#endif
     u8 *pReq = &pOrig[nReuse];
 
     /* Unmap any pages of the existing mapping that cannot be reused. */