llvm dev - Sep 2018 - How to get return address at llvm ir level?

Hi

I want to write a FunctionPass to insert some code before return.

Funcion:
..
..
..
mov eax,[esp]
cmp eax,0x12345678
je 0x12345678
ret
(maybe stack will not balance)

I wonder that can I get the return address at llvm ir level?

I use IRBuilder to CreateICmpEQ and CreateCondBr.

but I don't how to get the value of return addrss.

I have found there is a  Intrinsic::returnaddress.

Is Intrinsic::returnaddress can help me?

I don't konw how to use Intrinsic::returnaddress because few files use this
intrinsic.

Thanks
-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<http://lists.llvm.org/pipermail/llvm-dev/attachments/20180905/6b40c861/attachment.html>

Judging from the documentation, I'd say yes.
You can use intrinsics by importing them first using Intrinsics::getType and
Intrinsics::lookupLLVMIntrinsicsByName I think. Then just call them like any
other function. You might need to take special care with inline attributes and
whatnot though


Zhang
 
------------------ Original ------------------
From:  "PenYiWang via llvm-dev"<llvm-dev at lists.llvm.org>;
Date:  Wed, Sep 5, 2018 10:16 AM
To:  "llvm-dev"<llvm-dev at lists.llvm.org>; 

Subject:  [llvm-dev] How to get return address at llvm ir level?

 
Hi

I want to write a FunctionPass to insert some code before return.


Funcion:
..
..
..
mov eax,[esp]
cmp eax,0x12345678
je 0x12345678
ret
(maybe stack will not balance)


I wonder that can I get the return address at llvm ir level?


I use IRBuilder to CreateICmpEQ and CreateCondBr.


but I don't how to get the value of return addrss.


I have found there is a  Intrinsic::returnaddress.



Is Intrinsic::returnaddress can help me?


I don't konw how to use Intrinsic::returnaddress because few files use this
intrinsic.


Thanks
-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<http://lists.llvm.org/pipermail/llvm-dev/attachments/20180905/aa71006f/attachment.html>

> On Sep 4, 2018, at 10:16 PM, PenYiWang via llvm-dev <llvm-dev at
lists.llvm.org> wrote:
> 
> Hi
> 
> I want to write a FunctionPass to insert some code before return.
> 
> Funcion:
> ..
> ..
> ..
> mov eax,[esp]
> cmp eax,0x12345678
> je 0x12345678
> ret
> (maybe stack will not balance)
> 
> I wonder that can I get the return address at llvm ir level?
Short answer: You can’t 

Long answer: LLVM IR is a high level description, in comparison to assembly
code, of a program.
It “tries" to describe programs in a platform-independent fashion. However,
return address, even how a function pass its return data, is really platform and
architecture specific.

Nevertheless, your goal can still be achieved easily in LLVM. In your cases,
just iterates over all the instructions in a Function, find the return
instructions(i.e. those who are ReturnInst class instances), and insert the
desired things before them.
Of course, taking care of the data dependencies and/or control dependencies when
you insert instructions

> 
> I use IRBuilder to CreateICmpEQ and CreateCondBr.
This combination is for branches between BasicBlocks, not function returns.
> 
> but I don't how to get the value of return addrss.
> 
> I have found there is a  Intrinsic::returnaddress.
> 
> Is Intrinsic::returnaddress can help me?
Intrinsic functions in LLVM are usually used for special purposes. I’m certainly
sure that this Intrinsic::returnaddress is not what you want. Since it won’t be
generated by normal compiler frontend, and it would only place a function call
in IR without invoking it and gives you return address **when you’re doing code
optimizations**
> 
> I don't konw how to use Intrinsic::returnaddress because few files use
this intrinsic.
LLVM IR is neither (machine) assembly code nor something with the same role as
assembly code - It's a representation for, and should only be used for
compiler optimizations.
My suggestion is to read the official documents about [what is LLVM
IR](https://llvm.org/docs/LangRef.html#abstract
<https://llvm.org/docs/LangRef.html#abstract> ). It’s a nice introduction
and it’s not long.

Best,
Bekket
> 
> Thanks
> 
> 
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<http://lists.llvm.org/pipermail/llvm-dev/attachments/20180904/de1f6cc6/attachment.html>

To my knowledge that intrinsic IS generated by frontends like Clang when using
_builtin_return_address(), i could be wrong though

Zhang
> 在 2018年9月5日，10:47，Bekket McClane via llvm-dev <llvm-dev at
lists.llvm.org> 写道：
> 
> and