llvm dev - Aug 2018 - Replace "ret" with "pop+jump"

Hi

I want to replace all the return instructions in the program with pop
<reg>; jmp <reg>.

Should I use  IRBuilder in LLVM IR level?

I found that there is a IRBuilder::CreateIndirectBr

Or Should I modify the code in lib/Target/X86/X86ISelLowering.cpp in
backend ?

I found that there is a X86TargetLowering::LowerCall

Which is better?

Thanks
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IndirectBr only works for Branch instructions, not ret.
The latter one seems likely however I’m no where near a backend expert so I
could be wrong : (

Zhang
> 在 2018年8月9日，11:23，PenYiWang via llvm-dev <llvm-dev at lists.llvm.org>
写道：
> 
> Hi 
> 
> I want to replace all the return instructions in the program with pop
<reg>; jmp <reg>.
> 
> Should I use  IRBuilder in LLVM IR level?
> 
> I found that there is a IRBuilder::CreateIndirectBr
> 
> Or Should I modify the code in lib/Target/X86/X86ISelLowering.cpp in
backend ?
> 
> I found that there is a X86TargetLowering::LowerCall
> 
> Which is better?
> 
> Thanks
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev

You might be able to just check for the return instruction in
X86AsmPrinter::EmitInstruction where we convert from MachineInstr to
MCInst. You can change it to a POP and a JUMP MCInst.

~Craig


On Wed, Aug 8, 2018 at 8:31 PM mayuyu.io via llvm-dev <
llvm-dev at lists.llvm.org> wrote:
> IndirectBr only works for Branch instructions, not ret.
> The latter one seems likely however I’m no where near a backend expert so
> I could be wrong : (
>
> Zhang
>
> > 在 2018年8月9日，11:23，PenYiWang via llvm-dev <llvm-dev at
lists.llvm.org> 写道：
> >
> > Hi
> >
> > I want to replace all the return instructions in the program with pop
> <reg>; jmp <reg>.
> >
> > Should I use  IRBuilder in LLVM IR level?
> >
> > I found that there is a IRBuilder::CreateIndirectBr
> >
> > Or Should I modify the code in lib/Target/X86/X86ISelLowering.cpp in
> backend ?
> >
> > I found that there is a X86TargetLowering::LowerCall
> >
> > Which is better?
> >
> > Thanks
> > _______________________________________________
> > LLVM Developers mailing list
> > llvm-dev at lists.llvm.org
> > http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
>
>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
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Hey,
Legalization steps in X86ISelLowering.cpp seems like your way to go,
perhaps not even legalization and go straight away to LowerReturn.

On Thu, Aug 9, 2018 at 6:23 AM, PenYiWang via llvm-dev <
llvm-dev at lists.llvm.org> wrote:
> Hi
>
> I want to replace all the return instructions in the program with pop
> <reg>; jmp <reg>.
>
> Should I use  IRBuilder in LLVM IR level?
>
> I found that there is a IRBuilder::CreateIndirectBr
>
> Or Should I modify the code in lib/Target/X86/X86ISelLowering.cpp in
> backend ?
>
> I found that there is a X86TargetLowering::LowerCall
>
> Which is better?
>
> Thanks
>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
>
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