strerror: allow user hook to comply with POSIX rules

* libc/string/strerror.c (strerror): Split body into...
(_strerror_r): ...new reentrant function.
* libc/string/u_strerr.c (_user_strerror): Update signature.
* libc/include/stdio.h (_strerror_r): New prototype.
* libc/posix/collate.c (__collate_err): Adjust callers.
* libc/stdio/perror.c (_perror_r): Likewise.
* libc/string/strerror_r.c (strerror_r): Likewise.
* libc/string/xpg_strerror_r.c (__xpg_strerror_r): Likewise.

newlib/ChangeLog

@@ -1,3 +1,14 @@
+2011-05-25  Eric Blake  <eblake@redhat.com>
+
+	* libc/string/strerror.c (strerror): Split body into...
+	(_strerror_r): ...new reentrant function.
+	* libc/string/u_strerr.c (_user_strerror): Update signature.
+	* libc/include/stdio.h (_strerror_r): New prototype.
+	* libc/posix/collate.c (__collate_err): Adjust callers.
+	* libc/stdio/perror.c (_perror_r): Likewise.
+	* libc/string/strerror_r.c (strerror_r): Likewise.
+	* libc/string/xpg_strerror_r.c (__xpg_strerror_r): Likewise.
+
 2011-05-19  Yaakov Selkowitz  <yselkowitz@users.sourceforge.net>
 
 	* libc/include/stdio_ext.h: New header.

newlib/libc/include/string.h

@@ -96,6 +96,9 @@ char  *_EXFUN(strsignal, (int __signo));
 int     _EXFUN(strtosigno, (const char *__name));
 #endif
 
+/* Recursive version of strerror.  */
+char *	_EXFUN(_strerror_r, (struct _reent *, int, int, int *));
+
 /* These function names are used on Windows and perhaps other systems.  */
 #ifndef strcmpi
 #define strcmpi strcasecmp

newlib/libc/posix/collate.c

@@ -177,12 +177,13 @@ __collate_err(int ex, const char *f)
 {
 	const char *s;
 	int serrno = errno;
+	int dummy;
 
 	/* Be careful to change write counts if you change the strings */
 	write(STDERR_FILENO, "collate_error: ", 15);
 	write(STDERR_FILENO, f, strlen(f));
 	write(STDERR_FILENO, ": ", 2);
-	s = strerror(serrno);
+	s = _strerror_r(_REENT, serrno, 1, &dummy);
 	write(STDERR_FILENO, s, strlen(s));
 	write(STDERR_FILENO, "\n", 1);
 	exit(ex);

newlib/libc/stdio/perror.c

@@ -73,6 +73,7 @@ _DEFUN(_perror_r, (ptr, s),
        _CONST char *s)
 {
   char *error;
+  int dummy;
 
   _REENT_SMALL_CHECK_INIT (ptr);
   if (s != NULL && *s != '\0')
@@ -81,7 +82,7 @@ _DEFUN(_perror_r, (ptr, s),
       fputs (": ", _stderr_r (ptr));
     }
 
-  if ((error = strerror (ptr->_errno)) != NULL)
+  if ((error = _strerror_r (ptr, ptr->_errno, 1, &dummy)) != NULL)
     fputs (error, _stderr_r (ptr));
 
   fputc ('\n', _stderr_r (ptr));

newlib/libc/string/strerror.c

@@ -15,6 +15,8 @@ INDEX
 ANSI_SYNOPSIS
 	#include <string.h>
 	char *strerror(int <[errnum]>);
+	char *_strerror_r(struct _reent <[ptr]>, int <[errnum]>,
+			  int <[internal]>, int *<[error]>);
 
 TRAD_SYNOPSIS
 	#include <string.h>
@@ -288,6 +290,8 @@ Strings pipe error
 
 o-
 
+<<_strerror_r>> is a reentrant version of the above.
+
 RETURNS
 This function returns a pointer to a string.  Your application must
 not modify that string.
@@ -296,10 +300,10 @@ PORTABILITY
 ANSI C requires <<strerror>>, but does not specify the strings used
 for each error number.
 
-Although this implementation of <<strerror>> is reentrant, ANSI C
-declares that subsequent calls to <<strerror>> may overwrite the
-result string; therefore portable code cannot depend on the reentrancy
-of this subroutine.
+Although this implementation of <<strerror>> is reentrant (depending
+on <<_user_strerror>>), ANSI C declares that subsequent calls to
+<<strerror>> may overwrite the result string; therefore portable
+code cannot depend on the reentrancy of this subroutine.
 
 Although this implementation of <<strerror>> guarantees a non-null
 result with a NUL-terminator, some implementations return <<NULL>>
@@ -317,15 +321,24 @@ extensibility.  <<errno.h>> defines <[__ELASTERROR]>, which can be
 used as a base for user-defined error values.  If the user supplies a
 routine named <<_user_strerror>>, and <[errnum]> passed to
 <<strerror>> does not match any of the supported values,
-<<_user_strerror>> is called with <[errnum]> as its argument.
-
-<<_user_strerror>> takes one argument of type <[int]>, and returns a
-character pointer.  If <[errnum]> is unknown to <<_user_strerror>>,
-<<_user_strerror>> returns <[NULL]>.  The default <<_user_strerror>>
-returns <[NULL]> for all input values.
-
-Note that <<_user_sterror>> must be thread-safe and not alter <<errno>>
-if <<strerror_r>> is to comply with POSIX.
+<<_user_strerror>> is called with three arguments.  The first is of
+type <[int]>, and is the <[errnum]> value unknown to <<strerror>>.
+The second is of type <[int]>, and matches the <[internal]> argument
+of <<_strerror_r>>; this should be zero if called from <<strerror>>
+and non-zero if called from any other function; <<_user_strerror>> can
+use this information to satisfy the POSIX rule that no other
+standardized function can overwrite a static buffer reused by
+<<strerror>>.  The third is of type <[int *]>, and matches the
+<[error]> argument of <<_strerror_r>>; if a non-zero value is stored
+into that location (usually <[EINVAL]>), then <<strerror>> will set
+<<errno>> to that value, and the XPG variant of <<strerror_r>> will
+return that value instead of zero or <[ERANGE]>.  <<_user_strerror>>
+returns a <[char *]> value; returning <[NULL]> implies that the user
+function did not choose to handle <[errnum]>.  The default
+<<_user_strerror>> returns <[NULL]> for all input values.  Note that
+<<_user_sterror>> must be thread-safe, and only denote errors via the
+third argument rather than modifying <<errno>>, if <<strerror>> and
+<<strerror_r>> are are to comply with POSIX.
 
 <<strerror>> requires no supporting OS subroutines.
 
@@ -337,11 +350,14 @@ QUICKREF
 #include <string.h>
 
 char *
-_DEFUN (strerror, (errnum),
-	int errnum)
+_DEFUN (_strerror_r, (ptr, errnum, internal, errptr),
+	struct _reent *ptr _AND
+	int errnum _AND
+	int internal _AND
+	int *errptr)
 {
   char *error;
-  extern char *_user_strerror _PARAMS ((int));
+  extern char *_user_strerror _PARAMS ((int, int, int *));
 
   switch (errnum)
     {
@@ -798,10 +814,19 @@ _DEFUN (strerror, (errnum),
         break;
 #endif
     default:
-      if ((error = _user_strerror (errnum)) == 0)
-	error = "";
+      if (!errptr)
+        errptr = &ptr->_errno;
+      if ((error = _user_strerror (errnum, internal, errptr)) == 0)
+        error = "";
       break;
     }
 
   return error;
 }
+
+char *
+_DEFUN(strerror, (int),
+       int errnum)
+{
+  return _strerror_r (_REENT, errnum, 0, NULL);
+}

newlib/libc/string/strerror_r.c

@@ -43,7 +43,9 @@ PORTABILITY
 <<strerror_r>> with a <[char *]> result is a GNU extension.
 <<strerror_r>> with an <[int]> result is required by POSIX 2001.
 This function is compliant only if <<_user_strerror>> is not provided,
-or if it is thread-safe and does not modify <<errno>>.
+or if it is thread-safe and uses separate storage according to whether
+the second argument of that function is non-zero.  For more details
+on <<_user_strerror>>, see the <<strerror>> documentation.
 
 POSIX states that the contents of <[buf]> are unspecified on error,
 although this implementation guarantees a NUL-terminated string for
@@ -55,7 +57,7 @@ provides only an empty string (unless you provide <<_user_strerror>>).
 POSIX also recommends that unknown <[errnum]> fail with EINVAL even
 when providing such a message, however it is not a requirement and
 this implementation will return success if <<_user_strerror>> provided
-a non-empty alternate string.
+a non-empty alternate string without assigning into its third argument.
 
 <<strerror_r>> requires no supporting OS subroutines.
 
@@ -75,7 +77,7 @@ _DEFUN (strerror_r, (errnum, buffer, n),
 	char *buffer _AND
 	size_t n)
 {
-  char *error = strerror (errnum);
+  char *error = _strerror_r (_REENT, errnum, 1, NULL);
 
   if (strlen (error) >= n)
     return error;

newlib/libc/string/u_strerr.c

@@ -1,8 +1,10 @@
 #include <_ansi.h>
 
 char *
-_DEFUN(_user_strerror, (errnum),
-       int errnum)
+_DEFUN(_user_strerror, (errnum, internal, errptr),
+       int errnum _AND
+       int internal _AND
+       int *errptr)
 {
   return 0;
 }

newlib/libc/string/xpg_strerror_r.c

@@ -10,10 +10,11 @@ _DEFUN (__xpg_strerror_r, (errnum, buffer, n),
 	size_t n)
 {
   char *error;
+  int result = 0;
 
   if (!n)
     return ERANGE;
-  error = strerror (errnum);
+  error = _strerror_r (_REENT, errnum, 1, &result);
   if (strlen (error) >= n)
     {
       memcpy (buffer, error, n - 1);
@@ -21,5 +22,5 @@ _DEFUN (__xpg_strerror_r, (errnum, buffer, n),
       return ERANGE;
     }
   strcpy (buffer, error);
-  return *error ? 0 : EINVAL;
+  return (result || *error) ? result : EINVAL;
 }