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Date: Tue, 26 Jan 2021 12:23:31 -0500
From: Rich Felker <dalias@aerifal.cx>
To: Andrey Melnikov <temnota.am@gmail.com>
Cc: musl@lists.openwall.com
Message-ID: <20210126172330.GB23432@brightrain.aerifal.cx>
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User-Agent: Mutt/1.5.21 (2010-09-15)
Subject: [musl] Re: move __BYTE_ORDER definition to alltypes.h

On Tue, Jan 26, 2021 at 02:55:09PM +0300, Andrey Melnikov wrote:
> Hi.
> 
> Your commit 97d35a552ec5b6ddf7923dd2f9a8eb973526acea leads to
> miscompile programs which rely on one of defines __LITTLE_ENDIAN or
> __BIG_ENDIAN.
> Now, both unconditionally  defined when included stdarg.h and programs
> which define __(BIG|LITTE)_ENDIAN itself - miscompiled. linux kernel
> for example - it internally uses #if defined __BIG_ENDIAN and defines
> it only  for BIGENDAIN arches.
> 
> Any ideas?

The conditionally-defined macros that on some archs tell you the
endianness are __BIG_ENDIAN__ and __LITTLE_ENDIAN__ (note the final
__) or other arch-specific macros. __BIG_ENDIAN and __LITTLE_ENDIAN
(without the final __) have always been the possible values for
__BYTE_ORDER from endian.h. In any case, all of these are in the
reserved namespace and should not be defined by applications or
inspected in any way other than a manner documented by the
implementation.

How did this come up with the Linux kernel? AFAIK it uses -nostdinc
and should not see the libc headers at all. But if that #ifdef is
present in Linux it's probably a bug since it's contrary to all
historical use of __BIG_ENDIAN...

Rich