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
