[glibc] mach: Make xpg_strerror_r set a message on error

[Samuel Thibault <sthibaul@sourceware.org>]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=cb033e6b0ca7b8873cd00687ffd1828038a595d3

commit cb033e6b0ca7b8873cd00687ffd1828038a595d3
Author: Samuel Thibault <samuel.thibault@ens-lyon.org>
Date:   Sat Aug 27 14:46:23 2022 +0200

    mach: Make xpg_strerror_r set a message on error
    
    posix advises to have strerror_r fill a message even when we are returning
    an error.
    
    This makes mach's xpg_strerror_r do this, like the generic version does.
    
    Spotted by the libunistring testsuite test-strerror_r

Diff:
---
 sysdeps/mach/xpg-strerror.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/sysdeps/mach/xpg-strerror.c b/sysdeps/mach/xpg-strerror.c
index 92bb67e2bc..de75cc84ae 100644
--- a/sysdeps/mach/xpg-strerror.c
+++ b/sysdeps/mach/xpg-strerror.c
@@ -51,7 +51,11 @@ __xpg_strerror_r (int errnum, char *buf, size_t buflen)
   code = err_get_code (errnum);
 
   if (system > err_max_system || ! __mach_error_systems[system].bad_sub)
-    return EINVAL;
+    {
+      __snprintf (buf, buflen, "%s%X", _("Error in unknown error system: "),
+		  errnum);
+      return EINVAL;
+    }
 
   es = &__mach_error_systems[system];
 
@@ -62,11 +66,11 @@ __xpg_strerror_r (int errnum, char *buf, size_t buflen)
   else
     estr = (const char *) _(es->subsystem[sub].codes[code]);
 
-  size_t estrlen = strlen (estr) + 1;
+  size_t estrlen = strlen (estr);
 
-  if (buflen < estrlen)
-    return ERANGE;
+  /* Terminate the string in any case.  */
+  if (buflen > 0)
+    *((char *) __mempcpy (buf, estr, MIN (buflen - 1, estrlen))) = '\0';
 
-  memcpy (buf, estr, estrlen);
-  return 0;
+  return buflen <= estrlen ? ERANGE : 0;
 }