[PATCH][BUG FIX] Pointer arithmetic with NULL
Started by Ranier Vilelaabout 6 years ago2 messages
Hi,
Pointer addition with NULL, is technically undefined behavior.
Best regards.
Ranier Vilela
--- \dll\postgresql-12.0\a\backend\access\transam\xlog.c Mon Sep 30 17:06:55 2019
+++ xlog.c Fri Nov 22 13:57:17 2019
@@ -1861,7 +1861,7 @@
{
Assert(((XLogPageHeader) cachedPos)->xlp_magic == XLOG_PAGE_MAGIC);
Assert(((XLogPageHeader) cachedPos)->xlp_pageaddr == ptr - (ptr % XLOG_BLCKSZ));
- return cachedPos + ptr % XLOG_BLCKSZ;
+ return ptr % XLOG_BLCKSZ;
}/*
Attachments:
xlog.c.patchapplication/octet-stream; name=xlog.c.patchDownload
--- \dll\postgresql-12.0\a\backend\access\transam\xlog.c Mon Sep 30 17:06:55 2019
+++ xlog.c Fri Nov 22 13:57:17 2019
@@ -1861,7 +1861,7 @@
{
Assert(((XLogPageHeader) cachedPos)->xlp_magic == XLOG_PAGE_MAGIC);
Assert(((XLogPageHeader) cachedPos)->xlp_pageaddr == ptr - (ptr % XLOG_BLCKSZ));
- return cachedPos + ptr % XLOG_BLCKSZ;
+ return ptr % XLOG_BLCKSZ;
}
/*
Re: [PATCH][BUG FIX] Pointer arithmetic with NULL
On Fri, Nov 22, 2019 at 05:19:11PM +0000, Ranier Vilela wrote:
Hi,
Pointer addition with NULL, is technically undefined behavior.Best regards.
Ranier Vilela--- \dll\postgresql-12.0\a\backend\access\transam\xlog.c Mon Sep 30 17:06:55 2019 +++ xlog.c Fri Nov 22 13:57:17 2019 @@ -1861,7 +1861,7 @@ { Assert(((XLogPageHeader) cachedPos)->xlp_magic == XLOG_PAGE_MAGIC); Assert(((XLogPageHeader) cachedPos)->xlp_pageaddr == ptr - (ptr % XLOG_BLCKSZ)); - return cachedPos + ptr % XLOG_BLCKSZ; + return ptr % XLOG_BLCKSZ; }/*
But the value is not necessarily NULL, because it's defined like this:
static char *cachedPos = NULL;
that is, it's a static value - i.e. retained across multiple calls. The
question is whether we can get into that branch before it's set, but
it's certainly not correct to just remove it ...
regards
--
Tomas Vondra http://www.2ndQuadrant.com
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