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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@users.sourceforge.net>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>
[lersek@redhat.com: reconstruct commit from patch pasted into email]
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
This commit is contained in:
Zenith432 2017-12-12 18:12:11 +01:00 committed by Laszlo Ersek
parent 73d777329f
commit e3e40c83fd
1 changed files with 17 additions and 8 deletions
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25
MdePkg/Include/Base.h
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@ -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).