On Sat, Mar 23, 2019 at 08:31:53PM -0700, Nathan Chancellor wrote: > Explicitly cc'ing some folks who have touched include/linux/string.h in > the past and might want to take a look at this. > > Nathan
Thanks. One last revision with some nitpicks fixed is attached, though I doubt it'll influence any comments on the concept of this anyway. --- include/linux/string.h | 30 ++++++++++++++++++++++++++++++ 1 file changed, 30 insertions(+) diff --git a/include/linux/string.h b/include/linux/string.h index 7927b875f..40a8a9436 100644 --- a/include/linux/string.h +++ b/include/linux/string.h @@ -476,4 +476,34 @@ static __always_inline size_t str_has_prefix(const char *str, const char *prefix return strncmp(str, prefix, len) == 0 ? len : 0; } +/* + * Replace some common string helpers with faster alternatives when one of the + * arguments is a constant (i.e., literal string). This uses strlen instead of + * sizeof for calculating the string length in order to silence compiler + * warnings that may arise due to what the compiler thinks is incorrect sizeof + * usage. The strlen calls on constants are folded into scalar values at compile + * time, so performance is not reduced by using strlen. + */ +#define strcpy(dest, src) \ + __builtin_choose_expr(__builtin_constant_p(src), \ + memcpy((dest), (src), strlen(src) + 1), \ + (strcpy)((dest), (src))) + +#define strcat(dest, src) \ + __builtin_choose_expr(__builtin_constant_p(src), \ + ({ \ + memcpy((dest) + strlen(dest), (src), strlen(src) + 1); \ + (dest); \ + }), \ + (strcat)((dest), (src))) + +#define strcmp(left, right) \ + __builtin_choose_expr(__builtin_constant_p(left), \ + __builtin_choose_expr(__builtin_constant_p(right), \ + (strcmp)((left), (right)), \ + memcmp((left), (right), strlen(left) + 1)), \ + __builtin_choose_expr(__builtin_constant_p(right), \ + memcmp((left), (right), strlen(right) + 1), \ + (strcmp)((left), (right)))) + #endif /* _LINUX_STRING_H_ */ -- 2.21.0