[PATCH v4 2/2] x86: Update _dl_tlsdesc_dynamic to preserve caller-saved registers

[H.J. Lu]

On Fri, Feb 16, 2024 at 4:20 AM H.J. Lu <hjl.tools@gmail.com> wrote:
>
> On Fri, Feb 16, 2024 at 4:18 AM Florian Weimer <fweimer@redhat.com> wrote:
> >
> > * H. J. Lu:
> >
> > > On Thu, Feb 15, 2024 at 10:23 PM Florian Weimer <fweimer@redhat.com> wrote:
> > >>
> > >> * Adhemerval Zanella Netto:
> > >>
> > >> >> diff --git a/elf/malloc-for-test.map b/elf/malloc-for-test.map
> > >> >> new file mode 100644
> > >> >> index 0000000000..8437cf4346
> > >> >> --- /dev/null
> > >> >> +++ b/elf/malloc-for-test.map
> > >> >> @@ -0,0 +1,6 @@
> > >> >> +GLIBC_2.0 {
> > >> >
> > >> > You need to use the correct version to override the malloc:
> > >> >
> > >> > $ gdb --args tst-gnu2-tls2 --direct
> > >> > [...]
> > >> > (gdb) b apply_tls
> > >> > (gdb) r
> > >> > Thread 2 "tst-gnu2-tls2" hit Breakpoint 1, apply_tls (p=0x7ffff7bfee80) at tst-gnu2-tls2mod1.c:25
> > >> > 25 {
> > >> > (gdb) b malloc
> > >> > Breakpoint 2 at 0x7ffff7ca8ad0: malloc. (3 locations)
> > >> > (gdb) c
> > >> > Continuing.
> > >>
> > >> Why do we need to set a symbol version here?  I think this can be
> > >> removed.
> > >
> > > malloc-for-test.so provides a fake malloc to clobber caller-save
> > > registers.  Since malloc in ld.so has a symbol version,
> > >
> > >   struct r_found_version version;
> > >   version.name = symbol_version_string (libc, GLIBC_2_0);
> > >   version.hidden = 0;
> > >   version.hash = _dl_elf_hash (version.name);
> > >   version.filename = NULL;
> > >
> > >   void *new_calloc = lookup_malloc_symbol (main_map, "calloc", &version);
> > >   void *new_free = lookup_malloc_symbol (main_map, "free", &version);
> > >   void *new_malloc = lookup_malloc_symbol (main_map, "malloc", &version);
> > >   void *new_realloc = lookup_malloc_symbol (main_map, "realloc", &version);
> > >
> > > malloc in malloc-for-test.so must have the same version.  Otherwise,
> > > it won't be used in the test.
> >
> > I thought that unversioned symbols interpose all versioned symbols.  Has
> > this changed in the dynamic linker?
>
> Only for this case.
>

I was wrong.  Version isn't needed.  Will fix it.

Thanks.

-- 
H.J.