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Re: [PATCH 0/5] Add support for R_386_GOT32X/R_X86_64_[REX_]GOTPCRELX

On Mon, Jan 18, 2016 at 8:44 AM, Rafael EspÃndola
<> wrote:
>>> Sorry if I missed this somewhere else, but could you explain why we
>>> need these new relocations? Is it just to move work from the linker to
>>> the assembler or there was some correctness issue optimizing a plain
>>> R_X86_64_GOTPCREL?
>> They are used to convert memory operand of test and binop into
>> immediate operand, where binop is one of adc, add, and, cmp, or,
>> sbb, sub, xor instructions, when position-independent code is disabled.
>> The new relocation tells linker that it should try such optimization
>> since binop is one of mentioned above.
> But why not check the instruction in the linker? There is precedent,
> since the mov to lea transformation is done for R_X86_64_GOTPCREL.

Since for some binop, linker needs to rewrite the REX byte, it needs
to know if instruction has a REX byte.  R_X86_64_GOTPCREL doesn't
have such information


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