[PATCH] readelf: Handle 0 sh_entsize of GOT sections for x86

[H.J. Lu]

On Wed, Sep 3, 2025 at 5:24 PM Alan Modra <amodra@gmail.com> wrote:
>
> On Wed, Sep 03, 2025 at 04:28:30PM -0700, H.J. Lu wrote:
> > Some linker sets sh_entsize on .got and .got.plt sections, for example
> > x86-64 Google chrome browser:
> >
> > $ readelf -SW /opt/google/chrome/chrome | grep got
> >   [27] .got              PROGBITS        000000000fb29fc0 fb27fc0 001be0 00  WA  0   0  8
> >   [28] .got.plt          PROGBITS        000000000fb2bba0 fb29ba0 0029a8 00  WA  0   0  8
> > $
> >
> > If sh_entsize of GOT sections is 0 for x86, assume 4 for i386 and 8 for
> > x86-64.
> >
> >       PR binutils/33368
> >       * readelf.c (process_got_section_contents): Handle 0 sh_entsize
> >       of GOT sections for i386 and x86-64.
> >
> > Signed-off-by: H.J. Lu <hjl.tools@gmail.com>
> > ---
> >  binutils/readelf.c | 18 ++++++++++++++++++
> >  1 file changed, 18 insertions(+)
> >
> > diff --git a/binutils/readelf.c b/binutils/readelf.c
> > index 4b1a26602c2..c7a66d2a8e0 100644
> > --- a/binutils/readelf.c
> > +++ b/binutils/readelf.c
> > @@ -21150,6 +21150,24 @@ process_got_section_contents (Filedata * filedata)
> >         }
> >
> >       uint32_t entsz = section->sh_entsize;
> > +     /* NB: Some linker sets sh_entsize on .got and .got.plt
>
> You mean, "Some linkers don't set sh_entsize..."

Fixed in the v2 patch.

> > +        sections, for example x86-64 Google chrome browser.  */
> > +     if (entsz == 0)
> > +       switch (filedata->file_header.e_machine)
>
> Why only a fix for x86?  It seems reasonable to choose entsz based on
> file_header.e_ident[EI_CLASS].

Updated in the v2 patch to set it to 8 for ELFCLASS64 and skip with
a warning for ELFCLASS32 which may use 8, like x32.

>
> > +         {
> > +         default:
> > +           warn (_("Can't determine section '%s' sh_entsize\n"),
> > +                 name);
> > +           res = false;
> > +           goto out;
> > +         case EM_386:
> > +           entsz = 4;
> > +           break;
> > +         case EM_X86_64:
> > +           entsz = 8;
> > +           break;
> > +         }
> > +
> >       entries = section->sh_size / entsz;
> >       if (entries == 1)
> >         printf (_("\nGlobal Offset Table '%s' contains 1 entry:\n"),
> > --
> > 2.51.0
>
> --
> Alan Modra



-- 
H.J.