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

[kamlesh kumar via llvm-dev]

Thank you @Peter for the Info.

On Tue, Dec 10, 2019 at 5:15 PM Peter Smith <peter.smith at linaro.org> wrote:

> 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
> >>>
> >>>
> >>>
> >>> _______________________________________________
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> >>> llvm-dev at lists.llvm.org
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> >
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