[LLVMdev] [ARM] Mixing rel/rela relocations

[Eric Christopher]

On Mon, Nov 4, 2013 at 11:40 AM, Jack Carter <jack.carter at imgtec.com> wrote:

> On 11/04/2013 11:15 AM, Eric Christopher wrote:
>
>>
>>
>>
>> On Mon, Nov 4, 2013 at 11:05 AM, Shankar Easwaran
>> <shankare at codeaurora.org <mailto:shankare at codeaurora.org>> wrote:
>>
>>     Hi,
>>
>>     I was looking at the ARM ABI
>>     docs(http://infocenter.arm.__com/help/topic/com.arm.doc.__
>> ihi0044e/IHI0044E_aaelf.pdf
>>     <http://infocenter.arm.com/help/topic/com.arm.doc.
>> ihi0044e/IHI0044E_aaelf.pdf>)
>>
>>     and they mention.
>>
>>     "A binary file may use REL or RELA relocations or a mixture of the
>>     two (but multiple relocations for the same
>>     address must use only one type)."
>>
>>     Does LLVM emit rel/rela relocations with ARM ?
>>
>>
>> I hope not. Ew.
>>
>
> The only reason this is Ew is that llvm has decided not to prepare for it.
> There shouldn't be a single rel/rela type for a given output. The one that
> works for the given situation for the given section should be used. The
> mechanism for handling both should not be complicated.
>
> There are rules about relocation order and multiple relocations can
> operate on a single point in the binary. There is no reason a section of
> .rel relocations cannot operate alongside a section of .rela relocations.
>
>
True, however, I can think of no reasonable situation that you'd want to do
that. RELA has been around long enough that it's the default for just about
any ELF platform so the amount of legacy code is just someone not
implementing RELA as they should.

-eric


> Unfortunately I believe the single rel/rela type is part and parcel to gnu
> as well and I have resigned myself to going with the flow for now.
>
> Jack
>
>
>> -eric
>>
>>     Any tests ?
>>
>>     Thanks
>>
>>     Shankar Easwaran
>>
>>     --
>>     Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
>>     hosted by the Linux Foundation
>>
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