fortify: Fix spurious warning with realpath

The length and object size arguments were swapped around for realpath.
Also add a smoke test so that any changes in this area get caught in
future.

Signed-off-by: Siddhesh Poyarekar <siddhesh@sourceware.org>
Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
(cherry picked from commit 2bbd07c715275eb6c616988925738a0517180d57)

3 files changed, 40 insertions, 2 deletions

diff --git a/debug/Makefile b/debug/Makefile
index 357f888246..bc37e466ee 100644
--- a/debug/Makefile
+++ b/debug/Makefile
@@ -108,6 +108,7 @@ CFLAGS-tst-longjmp_chk2.c += -fexceptions -fasynchronous-unwind-tables
 CPPFLAGS-tst-longjmp_chk2.c += -D_FORTIFY_SOURCE=1
 CFLAGS-tst-longjmp_chk3.c += -fexceptions -fasynchronous-unwind-tables
 CPPFLAGS-tst-longjmp_chk3.c += -D_FORTIFY_SOURCE=1
+CPPFLAGS-tst-realpath-chk.c += -D_FORTIFY_SOURCE=2
 
 # We know these tests have problems with format strings, this is what
 # we are testing.  Disable that warning.  They are also testing
@@ -155,7 +156,7 @@ tests = backtrace-tst tst-longjmp_chk tst-chk1 tst-chk2 tst-chk3 \
 	tst-lfschk1 tst-lfschk2 tst-lfschk3 test-strcpy_chk test-stpcpy_chk \
 	tst-chk4 tst-chk5 tst-chk6 tst-chk7 tst-chk8 tst-lfschk4 tst-lfschk5 \
 	tst-lfschk6 tst-longjmp_chk2 tst-backtrace2 tst-backtrace3 \
-	tst-backtrace4 tst-backtrace5 tst-backtrace6
+	tst-backtrace4 tst-backtrace5 tst-backtrace6 tst-realpath-chk
 
 ifeq ($(have-ssp),yes)
 tests += tst-ssp-1
diff --git a/debug/tst-realpath-chk.c b/debug/tst-realpath-chk.c
new file mode 100644
index 0000000000..a8fcb327c4
--- /dev/null
+++ b/debug/tst-realpath-chk.c
@@ -0,0 +1,37 @@
+/* Smoke test to verify that realpath does not cause spurious warnings.
+   Copyright The GNU Toolchain Authors.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#include <limits.h>
+#include <stdlib.h>
+
+#include <support/check.h>
+#include <support/support.h>
+
+static int
+do_test (void)
+{
+#ifdef PATH_MAX
+  char buf[PATH_MAX + 1];
+  char *res = realpath (".", buf);
+  TEST_VERIFY (res == buf);
+#endif
+
+  return 0;
+}
+
+#include <support/test-driver.c>
diff --git a/stdlib/bits/stdlib.h b/stdlib/bits/stdlib.h
index 067115eeca..ccacbdf76a 100644
--- a/stdlib/bits/stdlib.h
+++ b/stdlib/bits/stdlib.h
@@ -42,7 +42,7 @@ __NTH (realpath (const char *__restrict __name, char *__restrict __resolved))
     return __realpath_alias (__name, __resolved);
 
 #if defined _LIBC_LIMITS_H_ && defined PATH_MAX
-  if (__glibc_unsafe_len (sz, sizeof (char), PATH_MAX))
+  if (__glibc_unsafe_len (PATH_MAX, sizeof (char), sz))
     return __realpath_chk_warn (__name, __resolved, sz);
 #endif
   return __realpath_chk (__name, __resolved, sz);