[PATCH] [libbacktrace] Initialize st in elf_is_symlink

[James Hilliard]

On Mon, Mar 18, 2019 at 6:58 PM Jeff Law <law@redhat.com> wrote:
>
> On 3/18/19 6:35 PM, James Hilliard wrote:
> > On Mon, Mar 18, 2019 at 5:46 PM Jeff Law <law@redhat.com> wrote:
> >>
> >> On 3/18/19 5:07 PM, James Hilliard wrote:
> >>> On Mon, Mar 18, 2019 at 4:51 PM Jakub Jelinek <jakub@redhat.com> wrote:
> >>>>
> >>>> On Mon, Mar 18, 2019 at 04:41:05PM -0600, James Hilliard wrote:
> >>>>>> Thanks, but I'm saying that if you look at the code you can see that
> >>>>>> st is clearly initialized, by the call to lstat.  I would like to see
> >>>>>> an explanation for why you are seeing that warning before changing the
> >>>>>> code to disable it.  Initializing st should not be necessary here.
> >>>>>> For example, perhaps lstat is a macro when compiling libsanitizer; if
> >>>>>> that is the underlying problem, then we should fix the macro, not this
> >>>>>> code.
> >>>>> Yeah, I'm not sure why the compiler thinks lstat isn't initializing st.
> >>>>> What should I do to debug this further?
> >>>>
> >>>> Guess you should start by telling us which OS it is on (I can't reproduce
> >>>> this warning on x86_64-linux nor i686-linux with glibc 2.28), looking at
> >>>> preprocessed source to see what exactly lstat does (e.g. if it is some macro
> >>>> or inline function and what exactly it is doing).
> >>> I am cross compiling with buildroot master branch using ubuntu 18.10.
> >>> I am building gcc 8.3.0 and glibc 2.29 for the cross toolchain.
> >>> The build and target systems are both x86_64.
> >> Add "-save-temps" to the command line.  That will create a .i file, send
> >> the .i file along with the command line.
> > I added --save-temps to the cflags for the gcc package build.
> > Here's the command line log:
> > https://gist.githubusercontent.com/jameshilliard/015d972c26d1ec7bbbd1ad2d57d5dd3b/raw/7c848cdfba0967a681401de24ed6f4c86315d2d9/cli.log
> > Here's the elf.i fille:
> > https://gist.githubusercontent.com/jameshilliard/2a391d7292f3ba7412fe80e166c0f0e3/raw/63eb16ba9eff0b3ee668b16257b0948b2ca894a0/elf.i
> Jakub -- I haven't looked at it in any detail, but the first thing that
> jumps out at me is the -Og and the message:
>
> > ../../../../libsanitizer/libbacktrace/../../libbacktrace/elf.c: In function ‘elf_is_symlink’:
> > ../../../../libsanitizer/libbacktrace/../../libbacktrace/elf.c:772:21: error: ‘st.st_mode’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
> >    return S_ISLNK (st.st_mode);
>
> It could be the issues we've see with SRA and aggregates that have led
> to the discussion around breaking those into a distinct class of uninit
> warnings because we don't handle them well.  I wouldn't be at all
> surprised if it goes away at -O1 or -O2.
I did a rebuild with -O2 and it worked.
>
> jeff