Wine's support for reporting calling conventions

[Roger Cruz]

In dlls/dbghelp/dwarf.c, there is this snippet of code which appears to hard-code the calling convention to CALL_FAR_C.  Does Wine not support reporting a function's calling convention correctly then?  Is it a limitation of DWARF or just that it is not implemented?  I can see that DWARF has a DW_AT_calling_convention field but when I examine a Wine DLL  with objdump, it does not show this field in use.

/* FIXME: assuming C source code */
    sig_type = symt_new_function_signature(ctx->module, ret_type, CV_CALL_FAR_C);

Thanks
Roger

[Eric Pouech]

that's a limitation of dwarf format (IIRC, from the specs, you have
either the default CC for your programming language/ABI, or a specific
one without defining it further)
FYII, the codeview format reports correctly this information
note also that winedbg doesn't support calling functions in the
debuggee, so this information is actually not used in winedbg
A+

2012/6/6, Roger Cruz :
> In dlls/dbghelp/dwarf.c, there is this snippet of code which appears to
> hard-code the calling convention to CALL_FAR_C.  Does Wine not support
> reporting a function's calling convention correctly then?  Is it a
> limitation of DWARF or just that it is not implemented?  I can see that
> DWARF has a DW_AT_calling_convention field but when I examine a Wine DLL
> with objdump, it does not show this field in use.
> /* FIXME: assuming C source code */
> sig_type = symt_new_function_signature(ctx->module, ret_type,
>
> CV_CALL_FAR_C);
>
> Thanks
> Roger

[Roger Cruz]

Hi Eric,

Thanks for replying.  I saw that in the DWARF spec and I was afraid that DWARF may not provide detailed Info. But I also read in the spec that the compilers use a DWARF extension feature to convey additional info such as calling convention for each routine.  Is there a way to coax GCC to output that information?  Maybe thru a target plugin?

Thanks
Roger

On Jun 6, 2012, at 3:06 AM, Eric Pouech  wrote:
> that's a limitation of dwarf format (IIRC, from the specs, you have
> either the default CC for your programming language/ABI, or a specific
> one without defining it further)
> FYII, the codeview format reports correctly this information
> note also that winedbg doesn't support calling functions in the
> debuggee, so this information is actually not used in winedbg
> A+
>
> 2012/6/6, Roger Cruz :
> > In dlls/dbghelp/dwarf.c, there is this snippet of code which appears to
> > hard-code the calling convention to CALL_FAR_C.  Does Wine not support
> > reporting a function's calling convention correctly then?  Is it a
> > limitation of DWARF or just that it is not implemented?  I can see that
> > DWARF has a DW_AT_calling_convention field but when I examine a Wine DLL
> > with objdump, it does not show this field in use.
> >
> > /* FIXME: assuming C source code */
> >    sig_type = symt_new_function_signature(ctx->module, ret_type,
> > CV_CALL_FAR_C);
> >
> > Thanks
> > Roger
> --
>
> Eric Pouech

[Eric Pouech]

dwarf4 allows each compiler vendor to add its own range of CC values
in the DW_AT_calling_convention field. this means that the vendor must
create its own table for mapping each used CC to a given value.
from a wine standpoint, the list should be rather small (stdcall,
fastcall...) (on top of cdecl of course) (assuming old 16bit code is
out of the game)

AFAIK, gcc only uses those extensions for very dedicated usage (pascal
compiler...). I don't see any reason why one couldn't extend gcc to do
it, but I cannot tell how complex it will be (and if plugins provide
the relevant interface to do so).
HTH
A+

2012/6/6, Roger Cruz :
> Hi Eric,
>
> Thanks for replying.  I saw that in the DWARF spec and I was afraid that
> DWARF may not provide detailed Info. But I also read in the spec that the
> compilers use a DWARF extension feature to convey additional info such as
> calling convention for each routine.  Is there a way to coax GCC to output
> that information?  Maybe thru a target plugin?

[Roger Cruz]

A previous google search did show up someone modifying GCC to add that level of CC info for another architecture so I'm sure it is something that we can do for x86.  I don't know how complex it would be either.  I was hoping it was already done and it was just a matter of a compiler flag.  I guess one more research task for me :-)
Regards,
Roger

________________________________
 From: Eric Pouech 
To: Roger Cruz  
Cc: Wine Devel  
Sent: Wednesday, June 6, 2012 8:12 AM
Subject: Re: Wine's support for reporting calling conventions

dwarf4 allows each compiler vendor to add its own range of CC values
in the DW_AT_calling_convention field. this means that the vendor must
create its own table for mapping each used CC to a given value.
from a wine standpoint, the list should be rather small (stdcall,
fastcall...) (on top of cdecl of course) (assuming old 16bit code is
out of the game)

AFAIK, gcc only uses those extensions for very dedicated usage (pascal
compiler...). I don't see any reason why one couldn't extend gcc to do
it, but I cannot tell how complex it will be (and if plugins provide
the relevant interface to do so).
HTH
A+

2012/6/6, Roger Cruz :
> Hi Eric,
>
> Thanks for replying.  I saw that in the DWARF spec and I was afraid that
> DWARF may not provide detailed Info. But I also read in the spec that the
> compilers use a DWARF extension feature to convey additional info such as
> calling convention for each routine.  Is there a way to coax GCC to output
> that information?  Maybe thru a target plugin?

[Jonas Maebe]

On 06 Jun 2012, at 09:06, Eric Pouech wrote:
> that's a limitation of dwarf format (IIRC, from the specs, you have
> either the default CC for your programming language/ABI, or a specific
> one without defining it further)

Yes and no:
* the DWARF standard itself does not specify any calling conventions other than DW_CC_normal (ABI default), DW_CC_program (Fortran-specific) and DW_CC_nocall (e.g. for interrupt handlers)
* however, the DWARF standard allows implementation-defined specific calling conventions to be added. I'm not aware of many that have been defined like that already, but a couple of them have been. E.g., search for DW_CC_ in http://gcc.gnu.org/svn/gcc/trunk/include/dwarf2.h . You need tool chain support (usually compiler support) to be able to generate such custom attributes though.

Jonas