https://sourceware.org/bugzilla/show_bug.cgi?id=32527
Bug ID: 32527
Summary: elfutils build warnings when building GCC -O3
Product: elfutils
Version: unspecified
Status: UNCONFIRMED
Severity: enhancement
Priority: P2
Component: general
Assignee: unassigned at sourceware dot org
Reporter: phi.debian at gmail dot com
CC: elfutils-devel at sourceware dot org
Target Milestone: ---
Hi
I used the component 'General' because the component 'libcpu' don't exist in
the selection list.
When building on ubuntu 24.04 GCC (and g++) 14.2.0 with options -m64 -O3 -g1 on
x86_64 and s390, we got warnings, yet make check show no errors, this is why I
marked this as 'enhancement'
The warnings occurs when building libcpu/i386_lex.o from i386_lex.l.
-------------------------
In function ‘i386__init_buffer’,
inlined from ‘i386_restart’ at i386_lex.c:1699:2:
i386_lex.c:1815:25: warning: potential null pointer dereference
[-Wnull-dereference]
1815 | b->yy_bs_column = 0;
| ~~~~~~~~~~~~~~~~^~~
i386_lex.c:1814:25: warning: potential null pointer dereference
[-Wnull-dereference]
...
-------------------------
Indeed this is not critical at all, but I try to build with no warnings.
The warning is due to the flex skeleton for lexer that use a pointer from
malloc() that could be NULL, even though this never happen except may be on
stressed systems, it is still possible, the punishment would be a core dump
though. This occurs only with gcc -O3, -O2 don't show this, clang never show
it.
I think gcc -O3 is right though, it do more inlining and discover the
potentially faulty unchecked malloc (we use the std def yymalloc == malloc)
Since we have little chance to get the lexer skeleton fixed from flex team, a
possible workaround is to add the option -Wno-null-dereference in the file
elfutils/libcpu/Makefile.am like this
i386_lex_CFLAGS = -Wno-unused-label -Wno-unused-function -Wno-sign-compare \
-Wno-implicit-fallthrough -Wno-null-dereference
By doing so, the warning disapear, we don't jeopardise anything, and it is
cleaner for the one who wants to build the perf path with no warnings.
Cheers,
Phi
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