Re: [PATCH v2] aarch64: Skip traditional GD/LD TLS which are unsupported by Clang and LLD [BZ #28205]

[Fangrui Song via Libc-alpha <libc-alpha@sourceware.org>]

On 2021-08-11, Fangrui Song wrote:
>On 2021-08-11, Szabolcs Nagy wrote:
>>The 08/10/2021 14:14, Fangrui Song via Libc-alpha wrote:
>>>On 2021-08-10, Fangrui Song wrote:
>>>> TLSDESC is the default on aarch64.  Clang doesn't support
>>>> -mtls-dialect=trad.  Its integrated assembler doesn't support the
>>>> marker.  LLD's doesn't support R_AARCH64_TLSGD_*/R_AARCH64_TLSLD_*
>>>> relocations.  Just skip the tests.
>>>>
>>>> With https://sourceware.org/pipermail/libc-alpha/2021-August/129966.html
>>>> ("aarch64: Make elf_machine_{load_address, dynamic} robust [BZ #28203]"),
>>>> if we allow LLD in configure.ac,
>>>> `make check` test results of LLD are on par with GNU ld.
>>>
>>>I messed up in the diff.
>>>The correct diff needs `#include <config.h>` to make HAVE_TRAD_TLS
>>>defined.
>>
>>the fixed patch looks good to me.
>>
>>but now i looked at elf/tls-macros.h and it seems
>>to be for when there is on compiler support.
>>
>>i think the only thing the compiler does not
>>support is mixing different tls access models to a
>>variable in the same tu, but i'm not sure if that's
>>useful or necessary for the tests: we can use many
>>files with different -ftls-model= or
>>__attribute__((tls_model(...))).
>>
>>is there a need for these hard to maintain macros?
>
>In GCC, mixing different tls access models to a variable in the same tu
>can be emulated by:
>
>  __thread int a __attribute__((tls_model("global-dynamic")));
>  extern __thread int b __attribute__((alias("a"), tls_model("initial-exec")));
>
>In Clang only one model is used.
>
>
>Seems a good idea to switch them to variable attributes.

alias() doesn't work. asm label works well.


https://sourceware.org/pipermail/libc-alpha/2021-August/130083.html
("elf: Drop elf/tls-macros.h in favor of __thread and tls_model attributes [BZ #28152] [BZ #28205]")
will modernize the tests.