[PATCH] D44355: [AArch64] Fold adds with tprel_lo12_nc and secrel_lo12 into a following ldr/str

[Martin Storsjö via Phabricator via llvm-commits]

mstorsjo added a comment.

In https://reviews.llvm.org/D44355#1036858, @peter.smith wrote:

> Unfortunately this change looks like it is going to be incompatible with binutils and LLD for the ELF targets as the ldr . The new output via llvm-objdump is:
>
>          0:	48 d0 3b d5 	mrs	x8, TPIDR_EL0
>          4:	08 01 40 91 	add	x8, x8, #0, lsl #12
>   		0000000000000004:  R_AARCH64_TLSLE_ADD_TPREL_HI12	tlsVar
>          8:	00 01 40 b9 	ldr	w0, [x8]
>   		0000000000000008:  R_AARCH64_TLSLE_LDST32_TPREL_LO12_NC	tlsVar
>          c:	c0 03 5f d6 	ret
>
>
> The GNU tools and LLD don't implement R_AARCH64_TLSLE_LDST32_TPREL_LO12_NC yet. For example using aarch64-linux-gnu-objdump:
>
>   0000000000000000 <getVar>:
>      0:	d53bd048 	mrs	x8, tpidr_el0
>      4:	91400108 	add	x8, x8, #0x0, lsl #12
>   			4: R_AARCH64_TLSLE_ADD_TPREL_HI12	tlsVar
>      8:	b9400100 	ldr	w0, [x8]
>   			8: *unknown*	tlsVar
>      c:	d65f03c0 	ret
>
>
> Whereas the equivalent add relocation R_AARCH64_TLSLE_ADD_TPREL_LO12 is supported.
>
> This is currently manifesting itself as a buildbot failure on AArch64 http://lab.llvm.org:8011/builders/clang-cmake-aarch64-full/builds/4609/steps/ninja%20check%202/logs/stdio
>
> I think we'll need to get R_AARCH64_TLSLE_ADD_TPREL_LO12 implemented in binutils and LLD and widely adopted by distributions before we can enable this by default, at least for Linux targets.


Oh, I hadn't realized that this relocation wasn't implemented for ELF even though it did exist in the LLVM object library. When working on TLS for windows, I implemented both the ADD and LDR/STR relocations at the same time, and MSVC uses the LDR/STR form by default.

I'm fine with reverting the ELF part of this change for now - I'll do that in a moment.


Repository:
  rL LLVM

https://reviews.llvm.org/D44355