linux-kernel - [PATCH v3 1/3] string: Make stpcpy() possible to use

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Date:   Wed, 26 Jan 2022 16:19:15 +0200
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Kees Cook <keescook@...omium.org>,
        Francis Laniel <laniel_francis@...vacyrequired.com>,
        Petr Mladek <pmladek@...e.com>, linux-kernel@...r.kernel.org
Cc:     Andy Shevchenko <andy@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        kernel test robot <lkp@...el.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nathan Chancellor <natechancellor@...il.com>
Subject: [PATCH v3 1/3] string: Make stpcpy() possible to use

It is a good rule to avoid submitting code without users.
Currently the stpcpy() is unusable due to missed declaration.
Any attempts to use it will bring something like:

  error: implicit declaration of function ‘stpcpy’ [-Werror=implicit-function-declaration]

Move declaration to the header and guard it as other string functions.

Fixes: 1e1b6d63d634 ("lib/string.c: implement stpcpy")
Reported-by: kernel test robot <lkp@...el.com>
Cc: Nick Desaulniers <ndesaulniers@...gle.com>
Cc: Nathan Chancellor <natechancellor@...il.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
---
v3: new patch to fix reported issue
 include/linux/string.h | 3 +++
 lib/string.c           | 3 ++-
 2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/include/linux/string.h b/include/linux/string.h
index b6572aeca2f5..b1aeb3475396 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
+char *stpcpy(char *__restrict__ dest, const char *__restrict__ src);
+#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 485777c9da83..4ecb8ec1fdd1 100644
--- a/lib/string.c
+++ b/lib/string.c
@@ -233,6 +233,7 @@ ssize_t strscpy(char *dest, const char *src, size_t count)
 EXPORT_SYMBOL(strscpy);
 #endif
 
+#ifndef __HAVE_ARCH_STPCPY
 /**
  * stpcpy - copy a string from src to dest returning a pointer to the new end
  *          of dest, including src's %NUL-terminator. May overrun dest.
@@ -248,7 +249,6 @@ EXPORT_SYMBOL(strscpy);
  * not recommended for usage. Instead, its definition is provided in case
  * the compiler lowers other libcalls to stpcpy.
  */
-char *stpcpy(char *__restrict__ dest, const char *__restrict__ src);
 char *stpcpy(char *__restrict__ dest, const char *__restrict__ src)
 {
 	while ((*dest++ = *src++) != '\0')
@@ -256,6 +256,7 @@ char *stpcpy(char *__restrict__ dest, const char *__restrict__ src)
 	return --dest;
 }
 EXPORT_SYMBOL(stpcpy);
+#endif
 
 #ifndef __HAVE_ARCH_STRCAT
 /**
-- 
2.34.1