Hi!
As mentioned in the PR, GCC (and clang) predefines
{__BYTE_ORDER__,__ORDER_{LITTLE,BIG,PDP}_ENDIAN__}
macros, and {,sys/,machine/}endian.h headers predefine
{,__}{BYTE_ORDER,{LITTLE,BIG,PDP}_ENDIAN}
macros (depending on which target and feature test macros).
elf.c in GCC 8 used __BYTE_ORDER, which is endian.h macro, but
didn't include that header and it on glibc just happened to be included
indirectly because of default feature test macros from stdlib.h,
and used non-existing __ORDER_BIG_ENDIAN macro; as __BYTE_ORDER is always
non-zero when defined (1234, 4321 etc.), that means __builtin_bswap32
was never used.
The following patch just uses the GCC/clang predefined macros if known to be
big or little endian, and otherwise just falls back to portable code (that
good compilers can still optimize).
Bootstrapped/regtested on x86_64-linux and i686-linux and tested on
powerpc64-linux, ok for trunk?
2018-04-03 Jakub Jelinek <ja...@redhat.com>
PR other/85161
* elf.c (elf_zlib_fetch): Fix up predefined macro names in test for
big endian, only use 32-bit loads if endianity macros are predefined
and indicate big or little endian.
--- libbacktrace/elf.c.jj 2018-02-15 12:30:53.948579969 +0100
+++ libbacktrace/elf.c 2018-04-03 14:47:32.536550472 +0200
@@ -1086,12 +1086,19 @@ elf_zlib_fetch (const unsigned char **pp
return 0;
}
+#if defined(__BYTE_ORDER__) && defined(__ORDER_LITTLE_ENDIAN__) \
+ && defined(__ORDER_BIG_ENDIAN__) \
+ && (__BYTE_ORDER__ == __ORDER_BIG_ENDIAN__ \
+ || __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__)
/* We've ensured that PIN is aligned. */
next = *(const uint32_t *)pin;
-#if __BYTE_ORDER == __ORDER_BIG_ENDIAN
+#if __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
next = __builtin_bswap32 (next);
#endif
+#else
+ next = pin[0] | (pin[1] << 8) | (pin[2] << 16) | (pin[3] << 24);
+#endif
val |= (uint64_t)next << bits;
bits += 32;
Jakub
