llvm dev - Jul 2008 - [LLVMdev] weird function

On Jul 23, 2008, at 11:31 AM, Duncan Sands wrote:
>> I  have tried to compile a simple cpp file with llvm-gcc. I have  
>> attached
>> the assemble file here.
>> I see a weird thing there. There are some call instructions, they  
>> call the
>> function "@_Znwj". But this function was only declared in the
file,
>> there is
>> no definition of it. So, how can it work, if this function is  
>> "empty" ?
>
> When you create a final executable using llvm-g++ it links with some  
> standard
> C++ libraries.  Probably @_Znwj is defined in one of those libraries.
_Znwj is aka "operator new".  You need to link to libstdc++.

-Chris

Hi,
 thank for your answer. Is there any document/tutorial about linking
bytecode file with libstdc++ avaiable ?

Quang

-----Ursprüngliche Nachricht-----
Von: llvmdev-bounces at cs.uiuc.edu [mailto:llvmdev-bounces at cs.uiuc.edu] Im
Auftrag von Chris Lattner
Gesendet: Mittwoch, 23. Juli 2008 20:35
An: LLVM Developers Mailing List
Cc: Le Anh Quang
Betreff: Re: [LLVMdev] weird function


On Jul 23, 2008, at 11:31 AM, Duncan Sands wrote:
>> I  have tried to compile a simple cpp file with llvm-gcc. I have  
>> attached
>> the assemble file here.
>> I see a weird thing there. There are some call instructions, they  
>> call the
>> function "@_Znwj". But this function was only declared in the
file,
>> there is
>> no definition of it. So, how can it work, if this function is  
>> "empty" ?
>
> When you create a final executable using llvm-g++ it links with some  
> standard
> C++ libraries.  Probably @_Znwj is defined in one of those libraries.
_Znwj is aka "operator new".  You need to link to libstdc++.

-Chris
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Hi,
>  thank for your answer. Is there any document/tutorial about linking
> bytecode file with libstdc++ avaiable ?
first you need to compile the bitcode to assembler using llc.
For example:
  llc bitcode.bc
This produces bitcode.s.  Turn this into a executable using:
  llvm-g++ -o bitcode bitcode.s
or
  g++ -o bitcode bitcode.s
It doesn't matter which g++ you use here.  Using g++ means
that your program will automatically be linked with libstdc++.

I hope this helps,

Duncan.