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

[Florian Weimer]

* 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?

Thanks,
Florian