diff options
Diffstat (limited to 'include/linux/compiler-gcc.h')
| -rw-r--r-- | include/linux/compiler-gcc.h | 19 |
1 files changed, 17 insertions, 2 deletions
diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h index 5c8351b859f0..1514d534deeb 100644 --- a/include/linux/compiler-gcc.h +++ b/include/linux/compiler-gcc.h @@ -11,9 +11,19 @@ /* The "volatile" is due to gcc bugs */ #define barrier() __asm__ __volatile__("": : :"memory") -/* This macro obfuscates arithmetic on a variable address so that gcc - shouldn't recognize the original var, and make assumptions about it */ /* + * This macro obfuscates arithmetic on a variable address so that gcc + * shouldn't recognize the original var, and make assumptions about it. + * + * This is needed because the C standard makes it undefined to do + * pointer arithmetic on "objects" outside their boundaries and the + * gcc optimizers assume this is the case. In particular they + * assume such arithmetic does not wrap. + * + * A miscompilation has been observed because of this on PPC. + * To work around it we hide the relationship of the pointer and the object + * using this macro. + * * Versions of the ppc64 compiler before 4.1 had a bug where use of * RELOC_HIDE could trash r30. The bug can be worked around by changing * the inline assembly constraint from =g to =r, in this particular @@ -61,3 +71,8 @@ #define noinline __attribute__((noinline)) #define __attribute_const__ __attribute__((__const__)) #define __maybe_unused __attribute__((unused)) + +#define __gcc_header(x) #x +#define _gcc_header(x) __gcc_header(linux/compiler-gcc##x.h) +#define gcc_header(x) _gcc_header(x) +#include gcc_header(__GNUC__) |