llvm dev - Jan 2013 - [LLVMdev] Question on using GlobalVariable as function pointer

Hi everyone,

  I am trying to have an call instruction that calls global variable


The first thing I do is

gv = new llvm::GlobalVariable( *(tb->getModule()),
		                          fty,
		                          false,GlobalValue::InternalLinkage,0,
		                          "",0,0,0);

fty : i32 ({ i32, [32 x i32] }*)


I get stuck here, the fifth argument is the initializer which is a LLVM
Constant,

I do not know how to describe a function pointer as a constant.

so currently, I just pass false to it.

then I use 

myjit->getOrEmitGlobalVariable(gv); // myjit is LLVM ExecutionEngine


but, I get an error

LLVM ERROR: Could not resolve external global address

However, when I modify fty to be an integer type or some primitive type,
there is no error.

Since LLVM demo page is closed, so I am not sure how to do it correctly.


Have A Nice Day

Chia Lun Liu



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Hi Chia Lun Liu,

On 07/01/13 03:38, ChiaLun wrote:
> Hi everyone,
>
>    I am trying to have an call instruction that calls global variable
>
>
> The first thing I do is
>
> gv = new llvm::GlobalVariable( *(tb->getModule()),
> 		                          fty,
> 		                          false,GlobalValue::InternalLinkage,0,
> 		                          "",0,0,0);
>
> fty : i32 ({ i32, [32 x i32] }*)
>
>
> I get stuck here, the fifth argument is the initializer which is a LLVM
> Constant,
>
> I do not know how to describe a function pointer as a constant.
>
> so currently, I just pass false to it.
If Func is the LLVM object of Function* type that represents the function you
want to call, then you can use it as the initial value.  The Function class
derives from the GlobalValue class, and the GlobalValue class derives from the
Constant class, thus anything of type Function* can be used wherever a Constant*
is required.

Ciao, Duncan.
>
> then I use
>
> myjit->getOrEmitGlobalVariable(gv); // myjit is LLVM ExecutionEngine
>
>
> but, I get an error
>
> LLVM ERROR: Could not resolve external global address
>
> However, when I modify fty to be an integer type or some primitive type,
> there is no error.
>
> Since LLVM demo page is closed, so I am not sure how to do it correctly.
>
>
> Have A Nice Day
>
> Chia Lun Liu
>
>
>
> --
> View this message in context:
http://llvm.1065342.n5.nabble.com/Question-on-using-GlobalVariable-as-function-pointer-tp53187.html
> Sent from the LLVM - Dev mailing list archive at Nabble.com.
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