llvm dev - Jul 2014 - [LLVMdev] Accessing a global and MCJIT

Hello,
I'm having a problem while accessing a global variable from a Module
compiled by the MCJIT.

For context, I have two modules (namely A and B). *Module A* is compiled by
clang, while *Module B *is compiled by the MCJIT.

In *Module A* I defined a global variable like this:
*@A = common global [800 x [800 x double]] zeroinitializer, align 16*

*Module B*, references that global like this:
*@A = external global [800 x [800 x double]]*

The problem that I have is that the MCJIT is not able to solve the symbol
for @A. I get the following error:

*LLVM ERROR: Program used external function 'A' which could not be
resolved!*

As far as I know, the MCJIT by default uses dlsym to solve the symbols. I
tried to get the address for *@A* using dlsym, but i get NULL.

After compiling *Module A*, I used llvm-nm to check the symbol table:

*0000000000608540 B A*
0000000000aea540 B B
0000000000fcc540 B C
00000000006081c8 d _DYNAMIC
0000000000608480 d _GLOBAL_OFFSET_TABLE_
0000000000402460 R _IO_stdin_used
....

Any clues?

Thank you,
-- 
Juan Manuel Martinez Caamaño, MSc.
PhD. Student, IRMA - Université de Strasbourg
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I suspect this comes down to how your linking module A.  If you directly 
pointing MCJIT at the object file, the common declaration is fine.  If 
not, you probably need to mark this as an explicit symbol.

According to the LangRef, a common symbol is not necessarily exported 
from the link step.  As a result, if you're building a shared library, 
the symbol won't be exported.

Philip

On 07/10/2014 02:16 AM, Juan Manuel Martinez Caamaño
wrote:
> Hello,
> I'm having a problem while accessing a global variable from a Module 
> compiled by the MCJIT.
>
> For context, I have two modules (namely A and B). /Module A/ is 
> compiled by clang, while /Module B /is compiled by the MCJIT.
>
> In /Module A/ I defined a global variable like this:
> /@A = common global [800 x [800 x double]] zeroinitializer, align 16/
>
> /Module B/, references that global like this:
> /@A = external global [800 x [800 x double]]/
>
> The problem that I have is that the MCJIT is not able to solve the 
> symbol for @A. I get the following error:
>
> /LLVM ERROR: Program used external function 'A' which could not be 
> resolved!/
>
> As far as I know, the MCJIT by default uses dlsym to solve the 
> symbols. I tried to get the address for /@A/ using dlsym, but i get NULL.
>
> After compiling /Module A/, I used llvm-nm to check the symbol table:
>
> *0000000000608540 B A*
> 0000000000aea540 B B
> 0000000000fcc540 B C
> 00000000006081c8 d _DYNAMIC
> 0000000000608480 d _GLOBAL_OFFSET_TABLE_
> 0000000000402460 R _IO_stdin_used
> ....
>
> Any clues?
>
> Thank you,
> -- 
> Juan Manuel Martinez Caamaño, MSc.
> PhD. Student, IRMA - Université de Strasbourg
>
>
> _______________________________________________
> 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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