On 3/24/20 10:18 AM, Jakub Jelinek wrote:
> Hi!
> 
> So, assuming I'm on glibc with GCC 4.5 on powerpc64-linux.
> 
> On Tue, Mar 24, 2020 at 09:49:42AM +0100, Martin Liška wrote:
>> +/* Detect endianess based on __BYTE_ORDER__ macro.  */
>> +#if defined(__BYTE_ORDER__) && defined(__ORDER_BIG_ENDIAN__) && \
>> +    defined(__ORDER_LITTLE_ENDIAN__) && defined(__ORDER_PDP_ENDIAN__)
>> +#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
>> +#define PLUGIN_LITTLE_ENDIAN 1
>> +#elif __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
>> +#define PLUGIN_BIG_ENDIAN 1
>> +#elif __BYTE_ORDER__ == __ORDER_PDP_ENDIAN__
>> +#define PLUGIN_PDP_ENDIAN 1
>> +#endif
>> +#else
>> +/* Older GCC releases (<4.6.0) can make detection from glibc macros.  */
>> +#if defined(__GLIBC__) || defined(__GNU_LIBRARY__) || defined(__ANDROID__)
>> +#include <endian.h>
>> +#if __BYTE_ORDER == __LITTLE_ENDIAN
>> +#define PLUGIN_LITTLE_ENDIAN 1
>> +#elif __BYTE_ORDER == __BIG_ENDIAN
>> +#define PLUGIN_BIG_ENDIAN 1
>> +#endif
> 
> This will definePLUGIN_BIG_ENDIAN.
> 
>> +#endif
>> +/* Include all necessary header files based on target.  */
>> +#if defined(__SVR4) && defined(__sun)
>> +#include <sys/byteorder.h>
>> +#endif
>> +#if defined(__FreeBSD__) || defined(__NetBSD__) || \
>> +    defined(__DragonFly__) || defined(__minix)
>> +#include <sys/endian.h>
>> +#endif
>> +#if defined(__OpenBSD__)
>> +#include <machine/endian.h>
>> +#endif
> 
> The above headers will not be included.
> 
>> +/* 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.

> 
>> +#elif _BYTE_ORDER == _BIG_ENDIAN
>> +#define PLUGIN_BIG_ENDIAN 1
>> +#endif
>> +/* Detect based on _WIN32.  */
>> +#if defined(_WIN32)
>> +#define PLUGIN_LITTLE_ENDIAN 1
>> +#endif
>> +/* Fallback to __BIG_ENDIAN__ and __LITTLE_ENDIAN__ */
>> +#ifdef __LITTLE_ENDIAN__
>> +#define PLUGIN_LITTLE_ENDIAN 1
>> +#endif
>> +#ifdef __BIG_ENDIAN__
>> +#define PLUGIN_BIG_ENDIAN 1
>> +#endif
>> +#endif
> 
> and the above isn't really a fallback, because it isn't guarded with
> PLUGIN_*_ENDIAN not being defined yet.

This comment has been also updated.

Martin

> 
> 	Jakub
>