Named local symbols in the ELF dynamic symbol table

[Florian Weimer]

* H. J. Lu:

> On Tue, Dec 6, 2022 at 9:11 AM Florian Weimer via Binutils
> <binutils@sourceware.org> wrote:
>>
>> The symbol table of /lib/ld-linux-ia64.so.2 starts like this:
>>
>> Symbol table [ 3] '.dynsym' contains 65 entries:
>>  33 local symbols  String table: [ 4] '.dynstr'
>>   Num:            Value   Size Type    Bind   Vis          Ndx Name
>>     0: 0000000000000000      0 NOTYPE  LOCAL  DEFAULT    UNDEF
>>     1: 00000000000318c0    160 FUNC    LOCAL  DEFAULT       10 _dl_error_free
>>     2: 00000000000234c0     16 FUNC    LOCAL  DEFAULT       10 __GI__dl_debug_state
>>     3: 0000000000029f80    368 FUNC    LOCAL  DEFAULT       10 _dl_tls_get_addr_soft
>>     4: 000000000002be00   1728 FUNC    LOCAL  DEFAULT       10 _dl_open
>>     5: 0000000000001550     64 FUNC    LOCAL  DEFAULT       10 _start
>>     6: 0000000000031540    784 FUNC    LOCAL  DEFAULT       10 _dl_runtime_profile
>>     7: 0000000000031440    208 FUNC    LOCAL  DEFAULT       10 _dl_runtime_resolve
>>     8: 00000000000312c0    384 FUNC    LOCAL  DEFAULT       10 _dl_close
>>     9: 0000000000018240  10720 FUNC    LOCAL  DEFAULT       10 _dl_lookup_symbol_x
>>    10: 000000000003ab40     80 FUNC    LOCAL  DEFAULT       10 _rtld_catch_error
>>
>> The interesting aspect is that these symbols are named, but are not
>> covered by the GNU_HASH table (because they are local).
>>
>> Is there a way to get the same effect on other targets?  I want to
>> preserve the names of the functions that IFUNC resolvers return,
>> eventually improving diagnostics around IFUNC resolution.  It would best
>> if I wouldn't have to bloat the entire symbol table for that.
>>
>
> Are you interested in R_X86_64_IRELATIVE symbols or something
> else?

Not particularly.  For ld.so --list-diagnostics, I want to iterate
through .dynsym, call all IFUNC resolvers, and report the results (for
libc, libm, libmvec at least).  To make the IFUNC resolver *result* more
meaningful, I want to map back the addresses to symbols like
__memmove_avx_unaligned_erms, but at the same time, I do not want to
make the symbol name __memmove_avx_unaligned_erms available for symbol
binding.  A local symbol in .dynsym would be a good fit here.

We can do this for IRELATIVE relocations, too, but it might be less
beneficial.

Thanks,
Florian