Merged revisions 129968 via svnmerge from

https://origsvn.digium.com/svn/asterisk/trunk

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r129968 | kpfleming | 2008-07-11 09:16:15 -0500 (Fri, 11 Jul 2008) | 18 lines

Merged revisions 129966 via svnmerge from 
https://origsvn.digium.com/svn/asterisk/branches/1.4

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r129966 | kpfleming | 2008-07-11 09:03:52 -0500 (Fri, 11 Jul 2008) | 5 lines

fix a flaw found while experimenting with structure alignment and padding; low-fence checking would not work properly on 64-bit platforms, because the compiler was putting 4 bytes of padding between the fence field and the allocation memory block

added a very obvious runtime warning if this condition reoccurs, so the developer who broke it can be chastised into fixing it :-)


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r129967 | kpfleming | 2008-07-11 09:03:52 -0500 (Fri, 11 Jul 2008) | 5 lines

simplify calculation

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git-svn-id: http://svn.digium.com/svn/asterisk/branches/1.6.0@129969 f38db490-d61c-443f-a65b-d21fe96a405b

1 files changed, 19 insertions, 1 deletions

diff --git a/main/astmm.c b/main/astmm.c
index f14ab8bdc..04a19037d 100644
--- a/main/astmm.c
+++ b/main/astmm.c
@@ -30,6 +30,7 @@
 ASTERISK_FILE_VERSION(__FILE__, "$Revision$")
 
 #include "asterisk/paths.h"	/* use ast_config_AST_LOG_DIR */
+#include <stddef.h>
 #include <time.h>
 
 #include "asterisk/cli.h"
@@ -63,14 +64,26 @@ enum func_type {
 
 static FILE *mmlog;
 
+/* NOTE: Be EXTREMELY careful with modifying this structure; the total size of this structure
+   must result in 'automatic' alignment so that the 'fence' field lands exactly at the end of
+   the structure in memory (and thus immediately before the allocated region the fence is
+   supposed to be used to monitor). In other words, we cannot allow the compiler to insert
+   any padding between this structure and anything following it, so add up the sizes of all the
+   fields and compare to sizeof(struct ast_region)... if they don't match, then the compiler
+   is padding the structure and either the fields need to be rearranged to eliminate internal
+   padding, or a dummy field will need to be inserted before the 'fence' field to push it to
+   the end of the actual space it will consume. Note that this must be checked for both 32-bit
+   and 64-bit platforms, as the sizes of pointers and 'size_t' differ on these platforms.
+*/
+
 static struct ast_region {
 	struct ast_region *next;
+	size_t len;
 	char file[64];
 	char func[40];
 	unsigned int lineno;
 	enum func_type which;
 	unsigned int cache;		/* region was allocated as part of a cache pool */
-	size_t len;
 	unsigned int fence;
 	unsigned char data[0];
 } *regions[SOME_PRIME];
@@ -462,6 +475,11 @@ static struct ast_cli_entry cli_memory[] = {
 void __ast_mm_init(void)
 {
 	char filename[PATH_MAX];
+	size_t pad = sizeof(struct ast_region) - offsetof(struct ast_region, data);
+
+	if (pad) {
+		ast_log(LOG_ERROR, "struct ast_region has %d bytes of padding! This must be eliminated for low-fence checking to work properly!\n", (int) pad);
+	}
 
 	ast_cli_register_multiple(cli_memory, sizeof(cli_memory) / sizeof(struct ast_cli_entry));