gdb/testsuite: XFAIL some gdb.base/fileio.exp

Some gdb.base/fileio.exp tests expect the inferior to not have write
access to some files. If the test is being run as root, this is never
possible. This commit adds a way to identify if the user is root and
xfails the tests that expect no write access.

Approved-By: Tom de Vries <tdevries@suse.de>

gdb/testsuite/gdb.base/fileio.exp

@@ -17,7 +17,6 @@
 
 require {!target_info exists gdb,nofileio}
 
-
 standard_testfile
 
 if {[is_remote host]} {
@@ -75,6 +74,10 @@ gdb_test "continue" ".*" ""
 
 catch "system \"chmod -f -w [standard_output_file nowrt.fileio.test]\""
 
+# If the user is root, we will always have write permission.
+if { [root_user] } {
+    setup_xfail *-*-*
+}
 gdb_test continue \
 "Continuing\\..*open 5:.*EACCES$stop_msg" \
 "Open for write but no write permission returns EACCES"
@@ -240,6 +243,10 @@ gdb_test continue \
 if [ishost *cygwin*] {
     setup_xfail "*-*-*"
 }
+# If the user is root, we will always have write permission.
+if { [root_user] } {
+    setup_xfail *-*-*
+}
 gdb_test continue \
 "Continuing\\..*unlink 2:.*EACCES$stop_msg" \
 "Unlinking a file in a directory w/o write access returns EACCES"

gdb/testsuite/lib/gdb.exp

@@ -10230,5 +10230,25 @@ gdb_caching_proc have_system_header { file } {
     return [gdb_can_simple_compile have_system_header_$name $src object]
 }
 
+# Return 1 if the test is being run as root, 0 otherwise.
+
+gdb_caching_proc root_user {} {
+    # ID outputs to stdout, we have to use exec to capture it here.
+    set res [remote_exec target id]
+    set ret_val [lindex $res 0]
+    set output [lindex $res 1]
+
+    # If ret_val is not 0, we couldn't run `id` on the target for some
+    # reason.  Return that we are not root, so problems are easier to
+    # spot.
+    if { $ret_val != 0 } {
+        return 0
+    }
+
+    regexp -all ".*uid=(\[0-9\]+).*" $output dummy uid
+
+    return [expr $uid == 0]
+}
+
 # Always load compatibility stuff.
 load_lib future.exp