[RFC PATCH] aarch64: ld: fix relaxations for ilp32 mode

[Jiong Wang]

On 17/01/17 08:48, Yury Norov wrote:
> On Mon, Jan 16, 2017 at 10:13:43AM +0000, Jiong Wang wrote:
>> On 14/01/17 10:48, Yury Norov wrote:
>>> Hi all,
>>>
>>> This patch continues the work of replacing 64-bit registers, offsets etc with
>>> 32-bit ones in elfNN_aarch64_tls_relax(). It doesn't fix any test I have tried,
>>> but it's generally correct, and I think that it should be applied.
>>>
>>> I also added new tests for ilp32 mode, and the problem is that some fail. So I'd
>>> like to ask for help here.
>>> Namely, 3 new tests are failed. tls-relax-large-desc-ie-ilp32 and
>>> tls-relax-large-desc-le-ilp32 fail due to error "cannot represent
>>> BFD_RELOC_AARCH64_TLSDESC_OFF_G1 relocation in this object file format", and
>>> test tls-desc-ie-ilp32 fails due to weird "undefined reference to `v2".
>>>
>>> If my understanding is correct, this error is because GAS cannot translate
>>> assembler commands to machine codes properly. If so, it may happen with some real
>>> program one day.
>>>
>>> It may also be my misunderstanding on how gas/ld work.
>> The "undefined reference to v2" is caused by missing of "-shared" in your linker command.
> Thank you, it works. My fail.
>
>> BFD_RELOC_AARCH64_TLSDESC_OFF_G1 and the several other relocations in the
>> error message are designed to be used by large code model only, so they are
>> not expected to be generated under ILP32.
> Hmm... Frankly, I don't understand how to proceed with that. The
> simplest way is to drop that couple of tests and resend the patch.
>
> But for me there's a problem here. If some asm file will contain the
> instruction sequence like in those tests, compilation will fail. It
> may come, say, from C inline asm, or whatsoever...
>
> Maybe we should wrap that relocations with "#if ARCH_SIZE == 64 ... #endif"
> like it has been done for BFD_RELOC_AARCH64_TLSG_MOW_G1 and
> BFD_RELOC_AARCH64_TLSGD_MOVW_G0_NC?

That looks correct to me, simply move those existed relocations into the existed ARCH_SIZE == 64 check block.

>
> BTW, is there some nice guide to linker internals, particularly to
> relocations?

I am not aware of any except source code...

There is a aarch64 elf pdf here http://infocenter.arm.com/help/topic/com.arm.doc.ihi0056c/IHI0056C_beta_aaelf64.pdf, which listed relocations type supported on LP64 and ILP32.