[binutils-gdb] gdb/testsuite: fix intermittent failures in gdb.mi/mi-cmd-user-context.exp

[binutils-gdb] gdb/testsuite: fix intermittent failures in gdb.mi/mi-cmd-user-context.exp

[Simon Marchi]

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=9b571e28984a7fb757962be477322f89d2366c80

commit 9b571e28984a7fb757962be477322f89d2366c80
Author: Simon Marchi <simon.marchi@efficios.com>
Date:   Mon Apr 4 12:08:22 2022 -0400

    gdb/testsuite: fix intermittent failures in gdb.mi/mi-cmd-user-context.exp
    
    I got failures like this once on a CI:
    
        frame^M
        &"frame\n"^M
        ~"#0  child_sub_function () at /home/jenkins/workspace/binutils-gdb_master_build/arch/amd64/target_board/unix/src/binutils-gdb/gdb/testsuite/gdb.mi/user-selected-context-sync.c:33\n"^M
        ~"33\t    dummy = !dummy; /* thread loop line */\n"^M
        ^done^M
        (gdb) ^M
        FAIL: gdb.mi/mi-cmd-user-context.exp: frame 1 (unexpected output)
    
    The problem is that the test expects the following regexp:
    
      ".*#0  0x.*"
    
    And that typically works, when the output of the frame command looks
    like:
    
      #0  0x00005555555551bb in child_sub_function () at ...
    
    Note the lack of hexadecimal address in the failing case.  Whether or
    not the hexadecimal address is printed (roughly) depends on whether the
    current PC is at the beginning of a line.  So depending on where thread
    2 was when GDB stopped it (after thread 1 hit its breakpoint), we can
    get either output.  Adjust the regexps to not expect an hexadecimal
    prefix (0x) but a function name instead (either child_sub_function or
    child_function).  That one is always printed, and is also a good check
    that we are in the frame we expect.
    
    Note that for test "frame 5", we are showing a pthread frame (on my
    system), so the function name is internal to pthread, not something we
    can rely on.  In that case, it's almost certain that we are not at the
    beginning of a line, or that we don't have debug info, so I think it's
    fine to expect the hex prefix.
    
    And for test "frame 6", it's ok to _not_ expect a hex prefix (what the
    test currently does), since we are showing thread 1, which has hit a
    breakpoint placed at the beginning of a line.
    
    When testing this, Tom de Vries pointed out that the current test code
    doesn't ensure that the child threads are in child_sub_function when
    they are stopped.  If the scheduler chooses so, it is possible for the
    child threads to be still in the pthread_barrier_wait or child_function
    functions when they get stopped.  So that would be another racy failure
    waiting to happen.
    
    The only way I can think of to ensure the child threads are in the
    child_sub_function function when they get stopped is to synchronize the
    threads using some variables instead of pthread_barrier_wait.  So,
    replace the barrier with an array of flags (one per child thread).  Each
    child thread flips its flag in child_sub_function to allow the main
    thread to make progress and eventually hit the breakpoint.
    
    I copied user-selected-context-sync.c to a new mi-cmd-user-context.c and
    made modifications to that, to avoid interfering with
    user-selected-context-sync.exp.
    
    Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=29025
    Change-Id: I919673bbf9927158beb0e8b7e9e980b8d65eca90

Diff:
---
 gdb/testsuite/gdb.mi/mi-cmd-user-context.c   | 73 ++++++++++++++++++++++++++++
 gdb/testsuite/gdb.mi/mi-cmd-user-context.exp | 10 ++--
 2 files changed, 78 insertions(+), 5 deletions(-)

diff --git a/gdb/testsuite/gdb.mi/mi-cmd-user-context.c b/gdb/testsuite/gdb.mi/mi-cmd-user-context.c
new file mode 100644
index 00000000000..bb74ab86b20
--- /dev/null
+++ b/gdb/testsuite/gdb.mi/mi-cmd-user-context.c
@@ -0,0 +1,73 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2016-2022 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/>.
+
+*/
+
+#include <pthread.h>
+#include <unistd.h>
+#include <stdint.h>
+
+#define NUM_THREADS 2
+
+static volatile int unblock_main[NUM_THREADS];
+
+static void
+child_sub_function (int child_idx)
+{
+  volatile int dummy = 0;
+
+  unblock_main[child_idx] = 1;
+
+  while (1)
+    /* Dummy loop body to allow setting breakpoint.  */
+    dummy = !dummy; /* thread loop line */
+}
+
+static void *
+child_function (void *args)
+{
+  int child_idx = (int) (uintptr_t) args;
+
+  child_sub_function (child_idx); /* thread caller line */
+
+  return NULL;
+}
+
+int
+main (void)
+{
+  int i = 0;
+  pthread_t threads[NUM_THREADS];
+
+  /* Make the test exit eventually.  */
+  alarm (20);
+
+  for (i = 0; i < NUM_THREADS; i++)
+    pthread_create (&threads[i], NULL, child_function, (void *) (uintptr_t) i);
+
+  /* Wait for child threads to reach child_sub_function.  */
+  for (i = 0; i < NUM_THREADS; i++)
+    while (!unblock_main[i])
+      ;
+
+  volatile int dummy = 0;
+  while (1)
+    /* Dummy loop body to allow setting breakpoint.  */
+    dummy = !dummy; /* main break line */
+
+  return 0;
+}
diff --git a/gdb/testsuite/gdb.mi/mi-cmd-user-context.exp b/gdb/testsuite/gdb.mi/mi-cmd-user-context.exp
index d7417d5ea7c..e5fccdd2308 100644
--- a/gdb/testsuite/gdb.mi/mi-cmd-user-context.exp
+++ b/gdb/testsuite/gdb.mi/mi-cmd-user-context.exp
@@ -18,7 +18,7 @@
 
 load_lib mi-support.exp
 
-standard_testfile user-selected-context-sync.c
+standard_testfile
 
 if {[build_executable $testfile.exp $testfile ${srcfile} "debug pthreads"] == -1} {
     untested "failed to compile"
@@ -79,7 +79,7 @@ mi_gdb_test "thread" \
 
 # Check we're in frame 0.
 mi_gdb_test "frame" \
-    ".*#0  0x.*" \
+    ".*#0  .*child_sub_function .*" \
     "frame 1"
 
 # Ask about a different frame in the current thread, the current frame
@@ -93,7 +93,7 @@ mi_gdb_test "thread" \
     "info thread 6"
 
 mi_gdb_test "frame" \
-    ".*#0  0x.*" \
+    ".*#0  .*child_sub_function.*" \
     "frame 2"
 
 
@@ -108,7 +108,7 @@ mi_gdb_test "thread" \
     "info thread 7"
 
 mi_gdb_test "frame" \
-    ".*#0  0x.*" \
+    ".*#0  .*child_sub_function.*" \
     "frame 3"
 
 # Select a different frame in the current thread.  Despite the use of
@@ -123,7 +123,7 @@ mi_gdb_test "thread" \
     "info thread 8"
 
 mi_gdb_test "frame" \
-    ".*#1  0x.*" \
+    ".*#1  .*child_function.*" \
     "frame 4"
 
 # Similar to the previous test, but this time the --frame option is