On Wed, 2023-08-30 at 14:49 +0200, Mathieu Malaterre wrote:
> On Wed, Aug 30, 2023 at 2:32 PM Xi Ruoyao <xry111@xxxxxxxxxxx> wrote:
> >
> > On Wed, 2023-08-30 at 14:25 +0200, Mathieu Malaterre via Gcc-help wrote:
> > > Hi all,
> > >
> > > Consider the following silly c++ code (*), it compiles nicely using
> > > g++ 13.2 no warnings using either:
> > >
> > > % g++ -c -O2 -Wall -Wextra alt.cxx
> > >
> > > or
> > >
> > > % g++ -c -O0 -Wall -Wextra alt.cxx
> > >
> > > Is it possible to trigger a warning for this code (maybe I missed some
> > > gcc options) ?
> >
> > Analyzer does a better job for such a "complex" pattern:
> >
> > $ gcc -Wall -Wextra t.cc -fanalyzer -S
>
> Cool ! Documentation is somewhat unclear to me as `-fanalyzer` seems
> to be required (I cannot simply use
> -Wanalyzer-use-of-uninitialized-value) (*)
>
> Could someone confirm that my code cannot trigger one of the
> `fsanitize=undefined` logic ? valgrind sees the uninitialised read:
-fsanitize=undefined cannot detect any uninitialised use. OTOH -
fsanitize=memory is capable:
$ clang++ t.cc -fsanitize=memory
$ ./a.out
==969846==WARNING: MemorySanitizer: use-of-uninitialized-value
#0 0x5603db7b65f7 in cl(d) (/home/xry111/a.out+0xb55f7)
#1 0x5603db7b6709 in k() (/home/xry111/a.out+0xb5709)
#2 0x5603db7b67d8 in main (/home/xry111/a.out+0xb57d8)
#3 0x7ff2d9c27f59 in __libc_start_call_main /home/xry111/sources/lfs/glibc-2.38/csu/../sysdeps/nptl/libc_start_call_main.h:58:16
#4 0x7ff2d9c28024 in __libc_start_main@GLIBC_2.2.5 /home/xry111/sources/lfs/glibc-2.38/csu/../csu/libc-start.c:360:3
#5 0x5603db71f2d0 in _start /home/xry111/sources/lfs/glibc-2.38/csu/../sysdeps/x86_64/start.S:115
SUMMARY: MemorySanitizer: use-of-uninitialized-value (/home/xry111/a.out+0xb55f7) in cl(d)
Exiting
But unfortunately the memory sanitizer is only supported by Clang, not
GCC :(.
--
Xi Ruoyao <xry111@xxxxxxxxxxx>
School of Aerospace Science and Technology, Xidian University
