Re: [PATCH v2] lib/string.c: implement stpcpy

[Joe Perches <joe@perches.com>]

On Fri, 2020-08-14 at 19:09 -0700, Nick Desaulniers wrote:
> 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.  Calling `sprintf` with overlapping arguments
> was clarified in ISO C99 and POSIX.1-2001 to be undefined behavior.
> 
> `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.
[]
> diff --git 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__);

If __restrict__ is used, perhaps it should follow the
kernel style used by attributes like __iomem and __user

extern char *stpcpy(char __restrict *dest, const char __restrict *src);

(though I would lose the extern too)

char *stpcpy(char __restrict *dest, const char __restrict *src);