[llvm-dev] Find instruction's offset

[Bruce Hoult via llvm-dev]

LLVM creates something like assembly language (or even real assembly
language) and doesn't know the exact offset of an instruction within the
function (or section).

The assembler might create different sized instructions -- or even multiple
instructions -- from something that LLVM just thinks of as "an
instruction". For example because of different instruction encodings or
even instruction sequences being needed because of the size of immediate
values or branch offsets (often not even known until link time). Even
things such as whether or not a REX prefix is needed on AMD64 depends on
whether some register mentioned in the instruction is in the high 8
registers -- LLVM *could* pay attention to that, but I'd suspect it doesn't.

On some platforms, instructions within a function can even be added or
deleted by the *linker*.

Your best best may be to take the final linked program and run objdump on
it.


On Mon, Jan 23, 2017 at 8:29 PM, fami Hoseini via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> I don't know if my question was super easy or maybe it is not clear. I'm
> still in need of the answer and appreciate any help.When LLVM creates
> assembly code it should somehow create instructions' program counter
> (offset) right? how to get this information?
>
> Thank you,
> Fateme
>
>
> On Mon, Jan 9, 2017 at 5:07 PM, fami Hoseini <hoseini.f at gmail.com> wrote:
>
>> Hi,
>> Is there a way to get instruction's offset at compile time with llvm for
>> ARM?
>> I am trying to create a map between instructions at compile time and this
>> run-time info. Since PC is a relative value, I am trying to use the
>> instruction's offset as a constant property of instruction to create this
>> map. I think offset information should be available to create the
>> executable, if so where to find it?
>> Thank you for your help,
>> Fami
>>
>
>
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