[PATCH] D71143: [ELF][Hexagon] Add support for TLS IE relocations
Sid Manning via Phabricator via llvm-commits
llvm-commits at lists.llvm.org
Mon Jan 6 14:16:40 PST 2020
sidneym added a comment.
In D71143#1806565 <https://reviews.llvm.org/D71143#1806565>, @MaskRay wrote:
> I'd like to ask some questions which can help understand the situation better.
>
> - Does Hexagon have a binutils port or an alternative linker?
The binutils port was never made public. The internal linker can be downloaded with a click-thu license agreement, the same one needed to get to the ABI spec. That linker is a branch of mclinker.
> - Is -pie and -shared used a lot on Hexagon?
-pie isn't but shared is.
> - How is Hexagon's dynamic loader ld.so implemented? Is the source code available?
The code isn't yet available from Qualcomm but we have a port of MUSL and I don't think much more than adding the #defines to reloc.h and the files dlsym.s/tlsdesc.s was done. Nothing weird for hexagon.
> - How is TLS going to be used on Hexagon?
There isn't anything out of the ordinary in how it is used and it is necessary for C++11 support.
> - Is text relocations acceptable?
No. The reason I needed to add the -z notext in the -shared test was because technically the wrong relocations were being used. I did that so that I could condense the IE patch into a single file testcase.
> - Is it really impossible to use a PC-relative GOT address load on Hexagon? `R_GOT` on EM_386 has severe limitations. `EM_X86_64` fixed these issues. (I don't want to see newer architectures behave like it.)
The R_HEX_IE_GOT... are used for shared/pic code. As far as I know the R_HEX_IE_32_6_X/16_X.. are used only when building static code. The ABI has examples for both of these IE static and IE for PIC.
> I shall also mention that this is unfortunate.
>
>> bool canRelax = config->emachine != EM_ARM &&
>> config->emachine != EM_RISCV;
>
> RISC-V TLS has several problems. Its design/implementation was copied from ARM/MIPS. The two architectures really do not provide the best reference for TLS implementations. The RISC-V TLS implementation has several defects. I've reported a few bugs on the binutils bugzilla.
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https://reviews.llvm.org/D71143/new/
https://reviews.llvm.org/D71143
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