llvm dev - Jun 2018 - How to force an unused function declaration in clang

clang doesn't seem to respect __attribute__((used)) in C functions. Even if
I declare a function like the following:   __attribute__((used)) void
function(), then also it doesn't declare the function in its IR file if I
don't use the function. Is there any other way to force the declaration of
"unused" function declarations with clang.

I have hacked in clang 6.0.0 in tools/clang/lib/CodeGen/CodeGenModule.cpp
file. I changed in EmitGlobal function to detect if the function has
"used"
attribute and then if it has then use "GetOrCreateLLVMFunction" this
to
create the function declaration. However, this hack fails in some other
cases. Therefore I am looking for a proper way to do this.

Regards,
Soham Sinha
PhD Student, Department of Computer Science
Boston University
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Out of curiosity, how does an unused declaration affect the emitted object file

Zhang
> 在 2018年6月26日，08:48，Soham Sinha via llvm-dev <llvm-dev at
lists.llvm.org> 写道：
> 
> clang doesn't seem to respect __attribute__((used)) in C functions.
Even if I declare a function like the following:   __attribute__((used)) void
function(), then also it doesn't declare the function in its IR file if I
don't use the function. Is there any other way to force the declaration of
"unused" function declarations with clang.
> 
> I have hacked in clang 6.0.0 in tools/clang/lib/CodeGen/CodeGenModule.cpp
file. I changed in EmitGlobal function to detect if the function has
"used" attribute and then if it has then use
"GetOrCreateLLVMFunction" this to create the function declaration.
However, this hack fails in some other cases. Therefore I am looking for a
proper way to do this.
> 
> Regards,
> Soham Sinha
> PhD Student, Department of Computer Science
> Boston University
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev

For the same reason GCC allowed the attribute. Even if I want to use/inline
a function later on in the pipeline.

Regards,
Soham Sinha
PhD Student, Department of Computer Science
Boston University


On Tue, Jun 26, 2018 at 8:30 AM mayuyu.io <admin at mayuyu.io> wrote:
> Out of curiosity, how does an unused declaration affect the emitted object
> file
>
> Zhang
>
> > 在 2018年6月26日，08:48，Soham Sinha via llvm-dev <llvm-dev at
lists.llvm.org>
> 写道：
> >
> > clang doesn't seem to respect __attribute__((used)) in C
functions. Even
> if I declare a function like the following:   __attribute__((used)) void
> function(), then also it doesn't declare the function in its IR file if
I
> don't use the function. Is there any other way to force the declaration
of
> "unused" function declarations with clang.
> >
> > I have hacked in clang 6.0.0 in
> tools/clang/lib/CodeGen/CodeGenModule.cpp file. I changed in EmitGlobal
> function to detect if the function has "used" attribute and then
if it has
> then use "GetOrCreateLLVMFunction" this to create the function
declaration.
> However, this hack fails in some other cases. Therefore I am looking for a
> proper way to do this.
> >
> > Regards,
> > Soham Sinha
> > PhD Student, Department of Computer Science
> > Boston University
> > _______________________________________________
> > LLVM Developers mailing list
> > llvm-dev at lists.llvm.org
> > http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
>
>
>
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