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

[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.

-- 
H.J.