[llvm-dev] aarch64 do not generate debug info for tls var

[Peter Smith via llvm-dev]

On Tue, 10 Dec 2019 at 11:30, kamlesh kumar via llvm-dev
<llvm-dev at lists.llvm.org> wrote:
>
> GCC's behavior matches LLVM.
> so should we leave it?
>

There is some more information in https://reviews.llvm.org/D43860 . It
has been some time since I looked at this, so my memory is hazy. As I
understand it there isn't a way to express the relocation in debug
info, all the existing TLS relocations are defined for instructions
with small immediate field. If we use a non-TLS relocation linkers
will refuse to link the binary as only TLS relocations are permitted
to relocate against TLS symbols.

The AArch64 ABI
https://developer.arm.com/docs/ihi0056/f/elf-for-the-arm-64-bit-architecture-aarch64-abi-2019q2-documentation
has a contact email on the front page. If your reading matches D43860
it may be worth contacting the email address describing the problem.
With a new relocation type, and support in compilers and linkers this
may be possible to address.

Peter

> On Tue, Dec 10, 2019 at 12:54 PM David Blaikie <dblaikie at gmail.com> wrote:
>>
>> What does GCC do?
>>
>> On Mon, Dec 9, 2019 at 10:25 PM kamlesh kumar via llvm-dev <llvm-dev at lists.llvm.org> wrote:
>>>
>>> Hi Devs,
>>>
>>> consider below testcase
>>> $cat test.c
>>> __thread int mtls=1;
>>> void foo(){
>>> mtls++;
>>> }
>>>
>>> it emits this debug info for mtls
>>>
>>> 0x0000002a:   DW_TAG_variable
>>>                 DW_AT_name      ("mtls")
>>>                 DW_AT_type      (0x00000035 "int")
>>>                 DW_AT_external  (true)
>>>                 DW_AT_decl_file ("test.c")
>>>                 DW_AT_decl_line (1)
>>>
>>> which does not contain DW_AT_Location.
>>>
>>> Currently, aarch64 does not emit DW_AT_Location for TLS variables.
>>> I could see at this line, it says some restriction in aarch64 elf abi.
>>> https://github.com/llvm-mirror/llvm/blob/master/lib/Target/AArch64/AArch64TargetObjectFile.cpp#L24
>>>
>>> I would like to know community thoughts on this and is there any other way to tackle this, or we simply can not debug TLS variables for this architecture?
>>>
>>>
>>> ./Kamlesh
>>>
>>>
>>>
>>> _______________________________________________
>>> LLVM Developers mailing list
>>> llvm-dev at lists.llvm.org
>>> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev