llvm dev - Sep 2016 - How to insert instructions before each function calls?

> On 5 Sep 2016, at 11:49, SHUCAI YAO <yaos4 at mcmaster.ca> 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.

-- Dean

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!
Shucai
> -- Dean
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> On 5 Sep 2016, at 16:14, SHUCAI YAO <yaos4 at mcmaster.ca> wrote:
> 
> 
> 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.
> 
Yes, this is all upstream -- if you look in lib/CodeGen/XRayInstrument.cpp and
the associated lowering code for X86 in lib/Target/X86/X86MCInstLower.cpp and/or
search for PATCHABLE_RET in include/... and lib/... then that should give you a
better idea of how this works. :)

Cheers

-- Dean