[gdb] Fix 'not in executable format' error message

With trying to load a non-executable file into gdb, we run into PR26880:
...
$ gdb -q -batch test.c
"0x7ffc87bfc8d0s": not in executable format: \
  file format not recognized
...

The problem is caused by using %ps in combination with the error function
(note that confusingly, it does work in combination with the warning
function).

Fix this by using plain "%s" instead.

Tested on x86_64-linux.

gdb/ChangeLog:

2021-08-22  Tom de Vries  <tdevries@suse.de>

	PR gdb/26880
	* gdb/exec.c (exec_file_attach): Use %s instead of %ps in call to
	error function.

gdb/testsuite/ChangeLog:

2021-08-22  Tom de Vries  <tdevries@suse.de>

	PR gdb/26880
	* gdb.base/non-executable.exp: New file.

1 files changed, 32 insertions, 0 deletions

diff --git a/gdb/testsuite/gdb.base/non-executable.exp b/gdb/testsuite/gdb.base/non-executable.exp
new file mode 100644
index 0000000..4ae123a
--- /dev/null
+++ b/gdb/testsuite/gdb.base/non-executable.exp
@@ -0,0 +1,32 @@
+# Copyright 2021 Free Software Foundation, Inc.
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program 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 General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+# Check that loading an existing but non-executable file
+# results in the correct error message.
+
+set binfile "$srcdir/$subdir/$gdb_test_file_name.exp"
+
+clean_restart
+
+set re \
+    [list \
+	 "\"[string_to_regexp $binfile]\"" \
+	 "not in executable format" \
+	 "file format not recognized"]
+set re [join $re ": "]
+
+# Using gdb_load will generate a dejagnu ERROR, so use
+# plain file command instead.
+gdb_test "file $binfile" $re "error message"