https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114776
Bug ID: 114776
Summary: -Wuse-after-free analysis believes assert() but not
g_assert_null()
Product: gcc
Version: 13.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: alan.coopersmith at oracle dot com
Target Milestone: ---
Created attachment 57985
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=57985&action=edit
Test case
When reviewing the -Wuse-after-free error reported in:
https://gitlab.freedesktop.org/xorg/lib/libxmu/-/merge_requests/13
in which gcc gives a use-after-free warning for p in:
p2 = Xmureallocarray(p, 2, ALLOC_LIMIT);
g_assert_null(p2);
[...]
free(p);
even though the realloc failed and returned NULL and did not free p.
I found that the -Wuse-after-free warning went away if I changed
g_assert_null(p2);
to
assert(p2 == NULL);
so it appears something in the way g_assert_null from glib is defined
does not convince gcc that p2 must be NULL the way the simple system
assert does.
I've made a cut down test case, and can reproduce the false alarm with
gcc `pkg-config --cflags glib-2.0` -Wall -O2 -c realloc.c
using gcc 13.2.0 on Solaris 11.4.66 on x86-64. (The original report came
from a gentoo Linux user, and I reproduced on Debian Linux, so this isn't
OS-specific.)
Adding -DUSE_SYSTEM_ASSERT to the compiler command line makes the warning
go away.
