Re: [PATCH] MdePkg: correct and clarify documentation of VA_LIST in Base.h

["Gao, Liming" <liming.gao@intel.com>]

Laszlo:
  Thanks!

Reviewed-by: Liming Gao <liming.gao@intel.com>

> -----Original Message-----
> From: edk2-devel [mailto:edk2-devel-bounces@lists.01.org] On Behalf Of Laszlo Ersek
> Sent: Tuesday, December 12, 2017 6:39 PM
> To: Zenith432 <zenith432@users.sourceforge.net>; edk2-devel@lists.01.org
> Cc: Kinney, Michael D <michael.d.kinney@intel.com>; Gao, Liming <liming.gao@intel.com>
> Subject: Re: [edk2] [PATCH] MdePkg: correct and clarify documentation of VA_LIST in Base.h
> 
> On 12/12/17 11:24, Zenith432 wrote:
> > Below is an amended patch.
> >
> > I changed the wording in the notes a little to exclude a non-variadic
> > function using VA_START, and to remind that VA_COPY should also be
> > paired with VA_END.
> >
> > Also, if GCC gets its VA_COPY repaired, documentation may change to
> > allow to using VA_COPY
> > inside non-EFIAPI as well.
> > ---
> >
> > This is to resolve bug 457.
> > https://bugzilla.tianocore.org/show_bug.cgi?id=457
> >
> > Contributed-under: TianoCore Contribution Agreement 1.1
> > Signed-off-by: Zenith432 <zenith432 at users.sourceforge.net>
> > ---
> >  MdePkg/Include/Base.h | 25 +++++++++++++++++--------
> >  1 file changed, 17 insertions(+), 8 deletions(-)
> >
> > diff --git a/MdePkg/Include/Base.h b/MdePkg/Include/Base.h
> > index 02140a5a..4fd5161f 100644
> > --- a/MdePkg/Include/Base.h
> > +++ b/MdePkg/Include/Base.h
> > @@ -552,21 +552,24 @@ struct _LIST_ENTRY {
> >  #define  BASE_8EB    0x8000000000000000ULL
> >
> >  //
> > -//  Support for variable length argument lists using the ANSI standard.
> > +//  Support for variable argument lists in freestanding edk2 modules.
> >  //
> > -//  Since we are using the ANSI standard we used the standard naming and
> > -//  did not follow the coding convention
> > +//  For modules that use the ISO C library interfaces for variable
> > +//  argument lists, refer to "StdLib/Include/stdarg.h".
> >  //
> >  //  VA_LIST  - typedef for argument list.
> >  //  VA_START (VA_LIST Marker, argument before the ...) - Init Marker
> > for use.
> >  //  VA_END (VA_LIST Marker) - Clear Marker
> > -//  VA_ARG (VA_LIST Marker, var arg size) - Use Marker to get an
> > argument from
> > -//    the ... list. You must know the size and pass it in this macro.
> > +//  VA_ARG (VA_LIST Marker, var arg type) - Use Marker to get an
> > argument from
> > +//    the ... list. You must know the type and pass it in this macro.
> > Type
> > +//    must be compatible with the type of the actual next argument (as
> > promoted
> > +//    according to the default argument promotions.)
> >  //  VA_COPY (VA_LIST Dest, VA_LIST Start) - Initialize Dest as a copy
> > of Start.
> >  //
> > -//  example:
> > +//  Example:
> >  //
> >  //  UINTN
> > +//  EFIAPI
> >  //  ExampleVarArg (
> >  //    IN UINTN  NumberOfArgs,
> >  //    ...
> > @@ -582,15 +585,21 @@ struct _LIST_ENTRY {
> >  //    VA_START (Marker, NumberOfArgs);
> >  //    for (Index = 0, Result = 0; Index < NumberOfArgs; Index++) {
> >  //      //
> > -//      // The ... list is a series of UINTN values, so average them up.
> > +//      // The ... list is a series of UINTN values, so sum them up.
> >  //      //
> >  //      Result += VA_ARG (Marker, UINTN);
> >  //    }
> >  //
> >  //    VA_END (Marker);
> > -//    return Result
> > +//    return Result;
> >  //  }
> >  //
> > +//  Notes:
> > +//  - Functions that call VA_START() / VA_END() must have a variable
> > +//    argument list and must be declared EFIAPI.
> > +//  - Functions that call VA_COPY() / VA_END() must be declared EFIAPI.
> > +//  - Functions that only use VA_LIST and VA_ARG() need not be EFIAPI.
> > +//
> >
> >  /**
> >    Return the size of argument that has been aligned to sizeof (UINTN).
> 
> Reviewed-by: Laszlo Ersek <lersek@redhat.com>
> 
> (Liming, I can help with applying this patch, if you want that.)
> 
> Thanks!
> Laszlo
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