From 7b1d72a096e5ffef0cc82f7c2782cd7a6da84bb1 Mon Sep 17 00:00:00 2001
From: Satya B <satya.bn@sun.com>
Date: Wed, 25 Mar 2009 14:45:53 +0530
Subject: [PATCH] Fix for BUG#41541 - Valgrind warnings on packed MyISAM table

After the table is compressed by the myisampack utility,
opening the table by the server produces valgrind warnings.

This happens because when we try to read a record into the buffer
we alway assume that the remaining buffer to read is always equal
to word size(4 or 8 or 2 bytes) we read. Sometimes we have
remaining buffer size less than word size and trying to read the
entire word size will end up in valgrind errors.

Fixed by reading byte by byte when we detect the remaining buffer
size is less than the word size.
---
 myisam/mi_packrec.c            | 26 ++++++++++++++++++++++++++
 mysql-test/r/myisampack.result | 11 +++++++++++
 mysql-test/t/myisampack.test   | 19 +++++++++++++++++++
 3 files changed, 56 insertions(+)

diff --git a/myisam/mi_packrec.c b/myisam/mi_packrec.c
index ddcf0f33e61..df9a4d18a6c 100644
--- a/myisam/mi_packrec.c
+++ b/myisam/mi_packrec.c
@@ -1430,6 +1430,32 @@ static void fill_buffer(MI_BIT_BUFF *bit_buff)
     bit_buff->current_byte=0;
     return;
   }
+  else
+  {
+    uint len= 0;
+    uint i= 0;
+    /*
+      Check if the remaining buffer/record to read is less than the word size.
+      If so read byte by byte
+
+      Note: if this branch becomes a bottleneck it can be removed, assuming
+      that the second memory segment allocates 7 extra bytes (see
+      _mi_read_pack_info()).
+    */
+    len= bit_buff->end - bit_buff->pos;
+    if (len < (BITS_SAVED / 8))
+    {
+      bit_buff->current_byte= 0;
+      for (i=0 ; i < len ; i++)
+      {
+        bit_buff->current_byte+= (((uint) ((uchar) bit_buff->pos[len - i - 1]))
+                                                                    << (8 * i));
+      }
+      bit_buff->pos= bit_buff->end;
+      return;
+    }
+  }
+
 #if BITS_SAVED == 64
   bit_buff->current_byte=  ((((uint) ((uchar) bit_buff->pos[7]))) +
 			     (((uint) ((uchar) bit_buff->pos[6])) << 8) +
diff --git a/mysql-test/r/myisampack.result b/mysql-test/r/myisampack.result
index 5f39d318234..b4b200549a5 100644
--- a/mysql-test/r/myisampack.result
+++ b/mysql-test/r/myisampack.result
@@ -27,3 +27,14 @@ CHECK TABLE t1 EXTENDED;
 Table	Op	Msg_type	Msg_text
 test.t1	check	status	OK
 DROP TABLE t1;
+#
+# BUG#41541 - Valgrind warnings on packed MyISAM table
+#
+CREATE TABLE  t1(f1 VARCHAR(200), f2 TEXT);
+INSERT INTO  t1 VALUES ('foo', 'foo1'), ('bar', 'bar1');
+FLUSH TABLE t1;
+# Compress the table using MYISAMPACK tool
+SELECT COUNT(*) FROM t1;
+COUNT(*)
+1024
+DROP TABLE t1;
diff --git a/mysql-test/t/myisampack.test b/mysql-test/t/myisampack.test
index 6598af6318a..ace7afce88a 100644
--- a/mysql-test/t/myisampack.test
+++ b/mysql-test/t/myisampack.test
@@ -31,3 +31,22 @@ FLUSH TABLES;
 --exec $MYISAMCHK -s --unpack $MYSQLTEST_VARDIR/master-data/test/t1
 CHECK TABLE t1 EXTENDED;
 DROP TABLE t1;
+
+--echo #
+--echo # BUG#41541 - Valgrind warnings on packed MyISAM table
+--echo #
+CREATE TABLE  t1(f1 VARCHAR(200), f2 TEXT);
+INSERT INTO  t1 VALUES ('foo', 'foo1'), ('bar', 'bar1');
+let $i=9;
+--disable_query_log
+while ($i)
+{
+ INSERT INTO t1 SELECT * FROM t1; 
+ dec $i; 
+}
+--enable_query_log
+FLUSH TABLE t1; 
+--echo # Compress the table using MYISAMPACK tool
+--exec $MYISAMPACK $MYSQLTEST_VARDIR/master-data/test/t1
+SELECT COUNT(*) FROM t1;
+DROP TABLE t1;