[llvm-dev] How to insert instructions before each function calls?

SHUCAI YAO via llvm-dev llvm-dev at lists.llvm.org
Sun Sep 4 23:14:56 PDT 2016

2016年9月5日星期一,Dean Michael Berris <dean.berris at gmail.com> 写道:

> > On 5 Sep 2016, at 11:49, SHUCAI YAO <yaos4 at mcmaster.ca <javascript:;>>
> wrote:
> >
> > For the function call lowering, do you mean lowercall function? I did
> insert the instruction before the stack adjustments, but the inserted code
> appears in the prologue of the function, other than before the function
> call. Maybe I did something wrong with the iterator.
> >
> > So you mean I should insert a pseudo instruction in the machinefunction
> pass, then replace it when function call lowering?  (Like segemented stack
> implementation?)
> >
> Yes, inserting pseudo instructions in the MachineFunctionPass -- you might
> want to have a look at PATCHABLE_RET and how we handle this in XRay.
> Essentially the idea (which I saw Sanjoy Das do first) is to wrap the
> actual instruction (in this case, CALL or LEA, or something specific in the
> platform you're targeting) in a pseudo instruction that just lowers to the
> correct sequence. This gives you complete control of the actual assembly of
> the instructions that you're replacing.

Hi Dean,

Do you have any example for this?  I would like have a look at how you
handle this in XRay if it is possible.

Thank you very much!

> -- Dean
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