(apologies for butting in, I can't resist)
On 03/14/14 16:13, Ari Zigler wrote:
> Hi Andrew,
>
>
>
> Thanks for the clarification.
>
>
>
> We’re using GCC 4.6 and I saw in the tools_defs.txt that our EFIAPI
> definition is being mapped to GCC’s function attribute
> __attribute__(ms_abi) which tells the compiler to enforce ms ABI to the
> function defined with it.
>
> I also tracked down a GCC flag (-mabi=ms) which enforces ms ABI globally
> (to all of the functions in the source code).
>
> By inspecting the assembly code being generated with that flag and
> comparing it to the assembly code being generated with the EFIAPI in
> conjunction with SYSV ABI (GCC’s default ABI) I noticed that they both
> produce the same calling convention.
I'd assume that happens because they mean the same. From the gcc-4.8.2 info:
'-mabi=NAME'
Generate code for the specified calling convention.
Permissible values are 'sysv' for the ABI used on GNU/Linux and
other systems, and 'ms' for the Microsoft ABI. The default is
to use the Microsoft ABI when targeting Microsoft Windows and
the SysV ABI on all other systems. You can control this
behavior for a specific function by using the function
attribute 'ms_abi'/'sysv_abi'. *Note Function Attributes::.
'ms_abi/sysv_abi'
On 32-bit and 64-bit (i?86|x86_64)-*-* targets, you can use an
ABI attribute to indicate which calling convention should be
used for a function. The 'ms_abi' attribute tells the compiler
to use the Microsoft ABI, while the 'sysv_abi' attribute tells
the compiler to use the ABI used on GNU/Linux and other
systems. The default is to use the Microsoft ABI when
targeting Windows. On all other systems, the default is the
x86/AMD ABI.
Note, the 'ms_abi' attribute for Microsoft Windows 64-bit
targets currently requires the '-maccumulate-outgoing-args'
option.
> Would you recommend using GCC with –mabi=ms flag by default when
> compiling code for UEFI rather than count on the developer to add EFIAPI
> to public functions?
In edk2, use of EFIAPI is required on the affected types of functions.
If you build outside of edk2, I would still recommend the case-by-case
attribute (using a macro name like EFIAPI or anything else). You might
want to link your driver or application (statically) against a
system-provided library. Suppose this library takes some kind of
callback function when you initialize it; you'd pass it a pointer to a
function that you define. The library would probably not expect the
ms_abi calling convention (which your function would be compiled for if
you set -mabi=ms globally for the build).
I think it's best to be explicit about EFIAPI. Supposing your developer
works on Linux, and actually tests at least once each new function he
adds, a wrong calling convention should be very quickly noticed.
For example, gnu-efi seems to use EFIAPI explicitly.
Just my two cents; Andrew will probably have more insight.
Thanks
Laszlo
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