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

[Martin Liška]

On 3/31/20 3:27 PM, Maciej W. Rozycki 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.

Hello.

Nice catch!

> 
> 	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?

I've just installed the patch.
@H.J. Can you please pull it to bintuils?

> 
>   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.

I see your point, but note that sometimes a direction of a patch changes during
the mailing list discussion. And so that we end up with a commit message that
has a different name.

Anyway, thank you for your help.
Martin

> 
>    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
>