Re: [PATCH kernel v3] powerpc/makefile: Do not redefine $(CPP) for preprocessor

Hi!

On Mon, May 17, 2021 at 01:23:11PM +1000, Alexey Kardashevskiy wrote:

On 5/14/21 18:46, Segher Boessenkool wrote:

quoted

On Fri, May 14, 2021 at 11:42:32AM +0900, Masahiro Yamada wrote:

quoted

In my best guess, the reason why powerpc adding the endian flag to CPP
is this line in arch/powerpc/kernel/vdso64/vdso64.lds.S

#ifdef __LITTLE_ENDIAN__
OUTPUT_FORMAT("elf64-powerpcle", "elf64-powerpcle", "elf64-powerpcle")
#else
OUTPUT_FORMAT("elf64-powerpc", "elf64-powerpc", "elf64-powerpc")
#endif

Which is equivalent to

#ifdef __LITTLE_ENDIAN__
OUTPUT_FORMAT("elf64-powerpcle")
#else
OUTPUT_FORMAT("elf64-powerpc")
#endif

so please change that at the same time if you touch this :-)

"If you touch this" approach did not work well with this patch so sorry 
but no ;)

and for a separate patch, I'll have to dig since when it is equal, do 
you know?

Since 1994, when the three-arg version was introduced (the one-arg
version is from 1992).

quoted

quoted

__LITTLE_ENDIAN__  is defined by powerpc gcc and clang.

This predefined macro is required by the newer ABIs, but all older

That's good so I'll stick to it.

Great.

quoted

You can just write -mbig and -mlittle btw.  Those aren't available on
all targets, but neither are the long-winded -m{big,little}-endian
option names.  Pet peeve, I know :-)

I am looking the same guarantees across modern enough gcc and clang and 
I am not sure all of the above is valid for clang 10.0.something (or 
whatever we say we support) ;)

-mbig/-mlittle is supported in GCC since times immemorial.  Whether LLVM
supports it as well just depends on how good their emulation is, I have
no idea.


Segher