Re: Assembly symbol generation

[Daniel Lohmann <daniel dot lohmann at informatik dot uni-erlangen dot de>]

Andrew Haley wrote:
> Katana Steel writes:
>  > 
>  > I wonder why; when I compile a C++ file with a header which looks like this:
>  > #ifndef __headername_h
>  > #define __headername_h 1
>  > 
>  > #ifdef __cplusplus
>  > 
>  > extern "C" void function1(int,char*,int);
>  > extern "C" void function2(int,char*,int);
>  > 
>  > #endif
>  > 
>  > #endif
>  > 
>  > under x86 & x64 linux this creates the symbols (output from nm):
>  >         U  function1
>  >         U  function2
>  > and using cygwin & mingw (x86) it creates these symbols (output from nm):
>  >         U  _function1
>  >         U  _function2
>  > 
>  > is there a good reason for this? 
>
> The ABI says so.  The ABI allows programs generated by different tools
> to be linked together: it doesn't really matter what the convention
> is, as long as everyone on a particular platform agrees.
>
> The "_" prefix is in fact an old UNIX convention that was IIRC dropped
> by UNIX System V when it went over to ELF format binaries.

On most platforms there is also a -mno-underscores or 
-fno-leading-underscores or similar option available that can be used to 
suppress this anachronism.

Daniel




--
Dipl.-Inf. Daniel Lohmann (Wissenschaftlicher Mitarbeiter)
Friedrich-Alexander-Universität Erlangen-Nürnberg
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