llvm dev - Mar 2015 - [LLVMdev] Passing a function pointer as parameter to function call?

Dear all,


I'm writing an LLVM pass, and I want to insert a call instruction that
takes a function pointer as a parameter. The effect would be the same as
following:

atexit(foo);

Where foo is a function I insert with M.getOrInsertFunction(), which in
LLVM is a Function class.

I searched for a while and did not come up with a satisfying answer. Should
I create a Value class of pointer type, or a Int64Ty for a pointer? How do
I get the pointer to the function I create? I also tried passing foo as
Function* in LLVM as parameter to create CallInst directly, and I doesn't
seem to work.

Any hints and enlightenment is appreciated. Many thanks.


Regards,
Yours,
Kevin Hu
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Easiest thing to do would be to write the equivalent C code, throw it
through Clang, and look at the IR it produces.

On Thu, Mar 12, 2015 at 3:00 PM, Kevin Hu <hxy9243 at gmail.com> wrote:
> Dear all,
>
>
> I'm writing an LLVM pass, and I want to insert a call instruction that
> takes a function pointer as a parameter. The effect would be the same as
> following:
>
> atexit(foo);
>
> Where foo is a function I insert with M.getOrInsertFunction(), which in
> LLVM is a Function class.
>
> I searched for a while and did not come up with a satisfying answer.
> Should I create a Value class of pointer type, or a Int64Ty for a pointer?
> How do I get the pointer to the function I create? I also tried passing foo
> as Function* in LLVM as parameter to create CallInst directly, and I
> doesn't seem to work.
>
> Any hints and enlightenment is appreciated. Many thanks.
>
>
> Regards,
> Yours,
> Kevin Hu
>
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>
>
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Hi David,


Thanks very much.

I tried and the IR it produces is:

%call = call i32 @atexit(void ()* foo)

The problem is this still doesn't give me any clues how to produce the code
inside my LLVM pass. How do I get the pointer to this foo function?

Any hints?


Thank you.
Kevin Hu

On Thu, Mar 12, 2015 at 6:09 PM, David Blaikie <dblaikie at gmail.com>
wrote:
> Easiest thing to do would be to write the equivalent C code, throw it
> through Clang, and look at the IR it produces.
>
> On Thu, Mar 12, 2015 at 3:00 PM, Kevin Hu <hxy9243 at gmail.com>
wrote:
>
>> Dear all,
>>
>>
>> I'm writing an LLVM pass, and I want to insert a call instruction
that
>> takes a function pointer as a parameter. The effect would be the same
as
>> following:
>>
>> atexit(foo);
>>
>> Where foo is a function I insert with M.getOrInsertFunction(), which in
>> LLVM is a Function class.
>>
>> I searched for a while and did not come up with a satisfying answer.
>> Should I create a Value class of pointer type, or a Int64Ty for a
pointer?
>> How do I get the pointer to the function I create? I also tried passing
foo
>> as Function* in LLVM as parameter to create CallInst directly, and I
>> doesn't seem to work.
>>
>> Any hints and enlightenment is appreciated. Many thanks.
>>
>>
>> Regards,
>> Yours,
>> Kevin Hu
>>
>> _______________________________________________
>> LLVM Developers mailing list
>> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>>
>>
>

-- 
Yours,
X. Hu
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