Re: [PATCH] ld: Allow R_X86_64_GOTPCREL for call *__tls_get_addr@GOTPCREL(%rip)

[Jan Beulich <jbeulich@suse.com>]

On 06.01.2023 18:03, H.J. Lu via Binutils wrote:
> On Thu, Jan 5, 2023 at 1:06 PM Fangrui Song via Binutils
> <binutils@sourceware.org> wrote:
>>
>> _Thread_local int a;
>> int main() { return a; }
>>
>> % gcc -fno-plt -fpic a.c -fuse-ld=bfd -Wa,-mrelax-relocations=no
>> /usr/bin/ld.bfd: /tmp/ccSSBgrg.o: TLS transition from R_X86_64_TLSGD to R_X86_64_GOTTPOFF against `a' at 0xd in section `.text' failed
>> /usr/bin/ld.bfd: failed to set dynamic section sizes: bad value
>> collect2: error: ld returned 1 exit status
>>
>> This commit fixes the issue.
>>
>>     PR ld/24784
>>     * bfd/elf64-x86-64.c (elf_x86_64_check_tls_transition): Allow
>>       R_X86_64_GOTPCREL.
>> ---
>>  bfd/elf64-x86-64.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/bfd/elf64-x86-64.c b/bfd/elf64-x86-64.c
>> index 914f82d0151..095fe2e0fe6 100644
>> --- a/bfd/elf64-x86-64.c
>> +++ b/bfd/elf64-x86-64.c
>> @@ -1241,7 +1241,7 @@ elf_x86_64_check_tls_transition (bfd *abfd,
>>           if (largepic)
>>             return r_type == R_X86_64_PLTOFF64;
>>           else if (indirect_call)
>> -           return r_type == R_X86_64_GOTPCRELX;
>> +           return (r_type == R_X86_64_GOTPCRELX || r_type == R_X86_64_GOTPCREL);
>>           else
>>             return (r_type == R_X86_64_PC32 || r_type == R_X86_64_PLT32);
>>         }
>> --
>> 2.39.0.314.g84b9a713c41-goog
>>
> 
> Since the new TLS sequence was added after R_X86_64_GOTPCRELX was
> required for call, R_X86_64_GOTPCREL should be invalid in this TLS sequence.

While this may well be, would you mind pointing out (more to Fangrui than to
me) what bad his proposed change would do?

Jan