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

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

Laszlo:
  Have you any comments for this patch? Seemly, you discussed this topic in bugzillar. 

Thanks
Liming
> -----Original Message-----
> From: edk2-devel [mailto:edk2-devel-bounces@lists.01.org] On Behalf Of Zenith432
> Sent: Monday, December 11, 2017 10:58 PM
> To: Gao, Liming <liming.gao@intel.com>; edk2-devel@lists.01.org
> Cc: Kinney, Michael D <michael.d.kinney@intel.com>
> Subject: Re: [edk2] [PATCH] MdePkg: correct and clarify documentation of VA_LIST in Base.h
> 
> Yes, that's right, in mixed ABI on GCC 7.2 (which is what GCC5 toolchain in tools_def.sample creates...), VA_COPY when
> used inside native (non-EFIAPI) function causes incorrect code generation that leads to crash (it mistreats the
> __builtin_ms_va_list as a __builtin_sysv_va_list).
> 
> The same source code works in current versions of LLVM and Apple clang - so it's a compiler-specific bug.
> 
> The text I wrote
>  >> +//  -- VA_END, VA_ARG, VA_COPY, va_end, va_arg, and va_copy may be used
>  >> +//     in functions of either calling conventions.
> 
> is the hypothetical desired condition, but it depends on compilers generating proper code in mixed ABI.  It obviously
> does not hold for current GCC.
> 
> However, the part of the documentation to add EFIAPI to ExampleVarArg should definitely be fixed.  Using
> __builtin_ms_va_list (=VA_LIST) in a sysv_abi (native) function probably yields a compile-time diagnostic, and if not -
> generates code that crashes for sure.
> 
> On 11/12/2017 04:35 PM, Gao, Liming wrote:
> > Hi,
> >    I see you and Laszlo are still in discussion on GCC behavior. Because there is one bug in GCC compiler, the following functions in
> edk2 must be EFIAPI. Right?
> >
> > - functions that have a variable argument list and call VA_START / VA_END
> > - functions that call VA_COPY
> >
> > Thanks
> > Liming
> >> -----Original Message-----
> >> From: Zenith432 [mailto:zenith432@users.sourceforge.net]
> >> Sent: Sunday, December 10, 2017 11:43 PM
> >> To: Gao, Liming <liming.gao@intel.com>; edk2-devel@lists.01.org
> >> Cc: Kinney, Michael D <michael.d.kinney@intel.com>
> >> Subject: Re: [PATCH] MdePkg: correct and clarify documentation of VA_LIST in Base.h
> >>
> >> On 10/12/2017 03:53 PM, Gao, Liming wrote:
> >>> Could you add bug 457 link in the commit message?
> >> ---
> >> Subject: [PATCH] MdePkg: correct and clarify documentation of VA_LIST in Base.h
> >>
> >> 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 | 24 ++++++++++++++++++++----
> >>     1 file changed, 20 insertions(+), 4 deletions(-)
> >>
> >> diff --git a/MdePkg/Include/Base.h b/MdePkg/Include/Base.h
> >> index 02140a5a..19f36872 100644
> >> --- a/MdePkg/Include/Base.h
> >> +++ b/MdePkg/Include/Base.h
> >> @@ -560,13 +560,14 @@ struct _LIST_ENTRY {
> >>     //  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.
> >>     //  VA_COPY (VA_LIST Dest, VA_LIST Start) - Initialize Dest as a copy of Start.
> >>     //
> >> -//  example:
> >> +//  Example:
> >>     //
> >>     //  UINTN
> >> +//  EFIAPI
> >>     //  ExampleVarArg (
> >>     //    IN UINTN  NumberOfArgs,
> >>     //    ...
> >> @@ -582,7 +583,7 @@ 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);
> >>     //    }
> >> @@ -591,6 +592,21 @@ struct _LIST_ENTRY {
> >>     //    return Result
> >>     //  }
> >>     //
> >> +//  Notes:
> >> +//
> >> +//  This set of macros is intended to support variadic functions that
> >> +//  use the EFIAPI calling convention.  Variadic functions that use a
> >> +//  native calling convention should use stdarg.h.
> >> +//  In particular:
> >> +//  -- VA_START may only be used in a variadic EFIAPI function.
> >> +//  -- va_start may only be used in a variadic native function.
> >> +//  -- VA_START, VA_END, VA_ARG and VA_COPY may only be used on a VA_LIST.
> >> +//  -- va_start, va_end, va_arg and va_copy may only be used on a va_list.
> >> +//  -- Both VA_LIST or va_list may be passed as arguments to functions
> >> +//     of either EFIAPI or native calling conventions.
> >> +//  -- VA_END, VA_ARG, VA_COPY, va_end, va_arg, and va_copy may be used
> >> +//     in functions of either calling conventions.
> >> +//
> >>
> >>     /**
> >>       Return the size of argument that has been aligned to sizeof (UINTN).
> >> --
> >> 2.14.3
> >
> 
> _______________________________________________
> edk2-devel mailing list
> edk2-devel@lists.01.org
> https://lists.01.org/mailman/listinfo/edk2-devel