[Bug 40423] Firefox GLX test crashes with Mesa 7.12-devel, Gallium 0.4 on AMD JUNIPER

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=40423

--- Comment #17 from Benoit Jacob <bjacob at mozilla.com> 2011-09-25 09:18:10 PDT ---
(In reply to comment #16)
> Is there anything else I can test to help fix this?

Looking at the Valgrind error from comment 15, it suggests that
_mesa_make_extension_string (extensions.c:912) makes the assumption that it's
safe to read 4 bytes from a string and that assumption fails as the string is
empty with just 1 byte allocated (and set to 0) by calloc.

This kind of error is very commonly found in string manipulation and is
generally considered safe to ignore as it can hardly lead to a crash. Indeed,
AFAIK it could only crash if reading those 4 bytes led to crossing a (4k) page
boundary, which would mean that the pointer was not even 4-byte-aligned... It's
not inconceivable to have a Firefox-specific crash there as Firefox uses a
custom memory allocator (jemalloc).

What you could do to investigate this bug, if you can recompile Mesa, is add a
printf in _mesa_make_extension_string (extensions.c:912) to print this pointer.
And perhaps add a printf at the next line to see if it's there that we crash.

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