Messages in this thread | | | Date | Mon, 18 Mar 2019 13:53:51 +1100 (AEDT) | From | Finn Thain <> | Subject | Re: [m68k:master 1174/1174] arch/m68k/include/asm/string.h:72:25: warning: '__builtin_memcpy' forming offset 8 is out of the bounds [0, 7] |
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On Tue, 12 Mar 2019, I wrote:
> ... I did another experiment with the latter (forced inline) approach, > to see if some optimizations can still be used with -ffreestanding. > > diff --git a/include/linux/string.h b/include/linux/string.h > index 7927b875f80c..25b5bf689018 100644 > --- a/include/linux/string.h > +++ b/include/linux/string.h > @@ -436,6 +436,58 @@ __FORTIFY_INLINE char *strcpy(char *p, const char *q) > return p; > } > > +#else > + > +//__FORTIFY_INLINE char *strncpy(char *p, const char *q, __kernel_size_t size) > +//{ > +// return __builtin_strncpy(p, q, size); > +//} > + > +__FORTIFY_INLINE char *strcat(char *p, const char *q) > +{ > + return __builtin_strcat(p, q); > +} > + > +__FORTIFY_INLINE __kernel_size_t strlen(const char *p) > +{ > + return __builtin_strlen(p); > +} > + > +__FORTIFY_INLINE char *strncat(char *p, const char *q, __kernel_size_t count) > +{ > + return __builtin_strncat(p, q, count); > +} > + > +__FORTIFY_INLINE void *memset(void *p, int c, __kernel_size_t size) > +{ > + return __builtin_memset(p, c, size); > +} > + > +//__FORTIFY_INLINE void *memcpy(void *p, const void *q, __kernel_size_t size) > +//{ > +// return __builtin_memcpy(p, q, size); > +//} > + > +__FORTIFY_INLINE void *memmove(void *p, const void *q, __kernel_size_t size) > +{ > + return __builtin_memmove(p, q, size); > +} > + > +__FORTIFY_INLINE int memcmp(const void *p, const void *q, __kernel_size_t size) > +{ > + return __builtin_memcmp(p, q, size); > +} > + > +__FORTIFY_INLINE void *memchr(const void *p, int c, __kernel_size_t size) > +{ > + return __builtin_memchr(p, c, size); > +} > + > +__FORTIFY_INLINE char *strcpy(char *p, const char *q) > +{ > + return __builtin_strcpy(p, q); > +} > + > #endif > > /** > > > The result of this patch really is confusing. It still suppresses the > warning you raised: > > arch/m68k/include/asm/string.h:72:25: warning: '__builtin_memcpy' forming > offset 8 is out of the bounds [0, 7] [-Warray-bounds] > #define memcpy(d, s, n) __builtin_memcpy(d, s, n) > ^~~~~~~~~~~~~~~~~~~~~~~~~ > include/linux/string.h:456:3: note: in expansion of macro 'memcpy' > memcpy(dest, src, dest_len); > ^~~~~~ > > But it also causes new ones, because of __builtin_memset(): > > drivers/video/fbdev/core/fbcvt.c: In function 'fb_find_mode_cvt': > drivers/video/fbdev/core/fbcvt.c:312:16: warning: 'cvt.flags' may be used uninit ialized in this function [-Wmaybe-uninitialized] > cvt.flags |= FB_CVT_FLAG_MARGINS; > ^~ > > Apparently the compiler doesn't understand that __builtin_memset() has > the effect of initialization. Weird. >
The other weird thing is that this warning doesn't show up when CONFIG_FORTIFY_SOURCE=y, even though the technique is much the same, that is, __builtin_memset() gets wrapped in a static inline memset() function.
Anyway, a quick and dirty microbenchmark under qemu-m68k shows that this patch reduces system time for 'time find / -false' by approx. 10%.
Interestingly, the -ffreestanding option doesn't make much difference to this particular microbenchmark.
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