[PATCH v3] gdb: testsuite: fix wrong expected result in attach-pie-noexec.exp

[Tiezhu Yang <yangtiezhu@loongson.cn>]

If /proc/sys/kernel/yama/ptrace_scope is 1, when execute the test case
gdb.base/attach-pie-noexec.exp without superuser, the gdb.log shows the
following info:

  (gdb) attach 6500
  Attaching to process 6500
  ptrace: Operation not permitted.
  (gdb) PASS: gdb.base/attach-pie-noexec.exp: attach

It is obviously wrong, the expected result should be UNSUPPORTED in such
a case.

It is better to make can_spawn_for_attach to return false for this case.
It would have to setup a small test program, compile it to exec, spawn it
and try to attach to it.

With this patch, we can see "please check privileges and try again" in
the log info, and then we can do the following processes to test:
(1) set ptrace_scope as 0
    $ echo 0 | sudo tee /proc/sys/kernel/yama/ptrace_scope
    $ make check-gdb TESTS="gdb.base/attach-pie-noexec.exp"
(2) use sudo
    $ sudo make check-gdb TESTS="gdb.base/attach-pie-noexec.exp"

Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
---
 gdb/testsuite/lib/gdb.exp | 37 ++++++++++++++++++++++++++++++-------
 1 file changed, 30 insertions(+), 7 deletions(-)

diff --git a/gdb/testsuite/lib/gdb.exp b/gdb/testsuite/lib/gdb.exp
index 60f7b83571a..8af2c011a3e 100644
--- a/gdb/testsuite/lib/gdb.exp
+++ b/gdb/testsuite/lib/gdb.exp
@@ -5055,7 +5055,10 @@ proc gdb_exit { } {
 # Return true if we can spawn a program on the target and attach to
 # it.
 
-proc can_spawn_for_attach { } {
+gdb_caching_proc can_spawn_for_attach {
+    global gdb_prompt
+    set test "can spawn for attach"
+
     # We use exp_pid to get the inferior's pid, assuming that gives
     # back the pid of the program.  On remote boards, that would give
     # us instead the PID of e.g., the ssh client, etc.
@@ -5070,6 +5073,32 @@ proc can_spawn_for_attach { } {
 	return 0
     }
 
+    set me "can_spawn_for_attach"
+    set src { int main() { sleep (600); return 0; } }
+    if {![gdb_simple_compile $me $src executable]} {
+        return 0
+    }
+
+    set test_spawn_id [spawn_wait_for_attach $obj]
+    set test_pid [spawn_id_get_pid $test_spawn_id]
+
+    gdb_start
+    file delete $obj
+    gdb_test_multiple "attach $test_pid" $test {
+        -re "Attaching to process $test_pid\r\n.*No executable file now.*\r\n$gdb_prompt $" {
+          pass $test
+          kill_wait_spawned_process $test_spawn_id
+          return 1
+        }
+        -re "Attaching to process $test_pid\r\n.*ptrace: Operation not permitted\\.\r\n$gdb_prompt $" {
+          unsupported "$test (please check privileges and try again)"
+          kill_wait_spawned_process $test_spawn_id
+          return 0
+        }
+    }
+
+    kill_wait_spawned_process $test_spawn_id
+
     # Assume yes.
     return 1
 }
@@ -5119,12 +5148,6 @@ proc spawn_id_get_pid { spawn_id } {
 proc spawn_wait_for_attach { executable_list } {
     set spawn_id_list {}
 
-    if ![can_spawn_for_attach] {
-	# The caller should have checked can_spawn_for_attach itself
-	# before getting here.
-	error "can't spawn for attach with this target/board"
-    }
-
     foreach {executable} $executable_list {
 	# Note we use Expect's spawn, not Tcl's exec, because with
 	# spawn we control when to wait for/reap the process.  That
-- 
2.27.0