From: Nick Desaulniers
Sent: 15 August 2020 01:24
LLVM implemented a recent "libcall optimization" that lowers calls to `sprintf(dest, "%s", str)` where the return value is used to `stpcpy(dest, str) - dest`. This generally avoids the machinery involved in parsing format strings.
`stpcpy` is just like `strcpy` except:
- it returns the pointer to the new tail of `dest`. This allows you to chain multiple calls to `stpcpy` in one statement.
- it requires the parameters not to overlap. Calling `sprintf` with overlapping arguments was clarified in ISO C99 and POSIX.1-2001 to be undefined behavior.
`stpcpy` was first standardized in POSIX.1-2008.
Implement this so that we don't observe linkage failures due to missing symbol definitions for `stpcpy`.
.. ...
diff --git a/include/linux/string.h b/include/linux/string.h index b1f3894a0a3e..e570b9b10f50 100644 --- a/include/linux/string.h +++ b/include/linux/string.h @@ -31,6 +31,9 @@ size_t strlcpy(char *, const char *, size_t); #ifndef __HAVE_ARCH_STRSCPY ssize_t strscpy(char *, const char *, size_t); #endif +#ifndef __HAVE_ARCH_STPCPY +extern char *stpcpy(char *__restrict, const char *__restrict__); +#endif
/* Wraps calls to strscpy()/memset(), no arch specific code required */ ssize_t strscpy_pad(char *dest, const char *src, size_t count); diff --git a/lib/string.c b/lib/string.c index 6012c385fb31..81bc4d62c256 100644 --- a/lib/string.c +++ b/lib/string.c @@ -272,6 +272,29 @@ ssize_t strscpy_pad(char *dest, const char *src, size_t count) } EXPORT_SYMBOL(strscpy_pad);
+#ifndef __HAVE_ARCH_STPCPY
...
+#undef stpcpy +char *stpcpy(char *__restrict__ dest, const char *__restrict__ src) +{
- while ((*dest++ = *src++) != '\0')
/* nothing */;- return dest;
+} +#endif
Hmmmm.... Maybe the compiler should just inline the above?
OTOH there are faster copies on 64bit systems (for moderate length strings).
It would also be nicer if the compiler actually used/required a symbol in the 'reserved for the implementation' namespace. Then the linker should be able to do a fixup to a differently name symbol - if that is required.
But compiler writers enjoy making embedded coders life hell.
David
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