[PATCH] PR lto/94249: Correct endianness detection with the __BYTE_ORDER macro

[Richard Biener]

On Tue, Mar 31, 2020 at 3:28 PM Maciej W. Rozycki <macro@linux-mips.org> wrote:
>
> Correct an issue with GCC commit 906b3eb9df6c ("Improve endianess
> detection.") and fix a typo in the __BYTE_ORDER fallback macro check
> that causes compilation errors like:
>
> .../include/plugin-api.h:162:2: error: #error "Could not detect architecture endianess"
>
> on systems that do not provide the __BYTE_ORDER__ macro.
>
>         include/
>         PR lto/94249
>         * plugin-api.h: Fix a typo in the __BYTE_ORDER macro check.
> ---
> On Tue, 24 Mar 2020, Martin Liška wrote:
>
> > >> +/* Detect endianess based on _BYTE_ORDER.  */
> > >> +#if _BYTE_ORDER == _LITTLE_ENDIAN
> > >
> > > So most likely _BYTE_ORDER and _LITTLE_ENDIAN macros will not be defined.
> > > Which means this will be handled as #if 0 == 0 and override the
> > >> +#define PLUGIN_LITTLE_ENDIAN 1
> > >
> > > will define also PLUGIN_LITTLE_ENDIAN.
> >
> > Ok, for being sure, I've wrapped all equality comparison with corresponding
> > check of the LHS is defined.
>
>  This change, when merged into binutils, caused BFD to fail building in
> one of my configurations:
>
> In file included from .../bfd/elflink.c:31:
> .../bfd/../include/plugin-api.h:162:2: error: #error "Could not detect architecture endianess"
> make[4]: *** [elflink.lo] Error 1
>
> This is due to a missing underscore in the:
>
> #ifdef _BYTE_ORDER
>
> check.
>
>  OK to apply this hopefully obvious fix to GCC and then merge to binutils?

OK.

>  NB if posting as an attachment please try matching the message subject
> with the change heading as otherwise it takes a lot of effort to track the
> patch submission corresponding to a given commit.
>
>   Maciej
> ---
>  include/plugin-api.h |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> binutils-include-plugin-api-byte-order.diff
> Index: binutils/include/plugin-api.h
> ===================================================================
> --- binutils.orig/include/plugin-api.h
> +++ binutils/include/plugin-api.h
> @@ -51,7 +51,7 @@
>  /* Older GCC releases (<4.6.0) can make detection from glibc macros.  */
>  #if defined(__GLIBC__) || defined(__GNU_LIBRARY__) || defined(__ANDROID__)
>  #include <endian.h>
> -#ifdef _BYTE_ORDER
> +#ifdef __BYTE_ORDER
>  #if __BYTE_ORDER == __LITTLE_ENDIAN
>  #define PLUGIN_LITTLE_ENDIAN 1
>  #elif __BYTE_ORDER == __BIG_ENDIAN