[PATCH v3 8/8] gdb/testsuite: Add test to exercise multi-threaded AArch64 SVE inferiors

[Thiago Jung Bauermann <thiago.bauermann@linaro.org>]

This testcase exercises two scenarios with a multi-threaded inferior, one
proposed by Luis and another one proposed by Simon.

In the first scenario, one of the inferior threads changes its vector
length and then hits a breakpoint.  In the second one, the main thread hits
a breakpoint and then GDB switches to another thread.
---
 gdb/testsuite/gdb.arch/aarch64-sve-threads.c  | 125 ++++++++++++++++++
 .../gdb.arch/aarch64-sve-threads.exp          |  70 ++++++++++
 2 files changed, 195 insertions(+)
 create mode 100644 gdb/testsuite/gdb.arch/aarch64-sve-threads.c
 create mode 100644 gdb/testsuite/gdb.arch/aarch64-sve-threads.exp

diff --git a/gdb/testsuite/gdb.arch/aarch64-sve-threads.c b/gdb/testsuite/gdb.arch/aarch64-sve-threads.c
new file mode 100644
index 000000000000..7fad77008da3
--- /dev/null
+++ b/gdb/testsuite/gdb.arch/aarch64-sve-threads.c
@@ -0,0 +1,125 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2023 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/>.  */
+
+/* Exercise AArch64's Scalable Vector Extension in a multi-threaded program.  */
+
+#include <stdbool.h>
+#include <stdio.h>
+#include <pthread.h>
+#include <semaphore.h>
+#include <sys/prctl.h>
+#include <unistd.h>
+
+/* For one of the tests, the thread needs to sleep after setting the vector
+   length.  This variable is set by GDB.  */
+volatile bool should_sleep = false;
+
+/* Used to signal to the main thread that the additional thread's vector length
+   was changed.  */
+sem_t vl_changed;
+
+/* Start routine for the additional thread.  Sets a new vector length, sleeps if
+   requested then restores the original vector length.  */
+
+static void *
+thread_function (void *unused)
+{
+  unsigned int vl;
+  int rc;
+
+  rc = prctl (PR_SVE_GET_VL, 0, 0, 0, 0);
+  if (rc < 0)
+    {
+      perror ("FAILED to PR_SVE_GET_VL");
+      sem_post (&vl_changed);
+      return NULL;
+    }
+
+  vl = rc & PR_SVE_VL_LEN_MASK;
+
+  /* Decrease vector length by 16 bytes.  */
+  vl -= 16;
+
+  rc = prctl (PR_SVE_SET_VL, vl, 0, 0, 0, 0);
+  if (rc < 0)
+    {
+      perror ("FAILED to PR_SVE_SET_VL");
+      sem_post (&vl_changed);
+      return NULL;
+    }
+
+  /* Let the main thread continue.  */
+  rc = sem_post (&vl_changed);
+  if (rc != 0)
+    {
+      perror ("sem_post");
+      return NULL;
+    }
+
+  if (should_sleep)
+    sleep (10);
+
+  /* Restore original vector length.  */
+  vl += 16; /* break here 1 */
+
+  rc = prctl (PR_SVE_SET_VL, vl, 0, 0, 0, 0);
+  if (rc < 0)
+    {
+      perror ("FAILED to PR_SVE_SET_VL");
+      return NULL;
+    }
+
+  return NULL; /* break here 2 */
+}
+
+int
+main (int argc, char **argv)
+{
+  pthread_t thread;
+  int rc;
+
+  rc = sem_init (&vl_changed, 0, 0);
+  if (rc != 0)
+    {
+      perror ("sem_init");
+      return 1;
+    }
+
+  rc = pthread_create (&thread, NULL, thread_function, NULL);
+  if (rc != 0)
+    {
+      perror ("pthread_create");
+      return 1;
+    }
+
+  /* Wait until the additional thread changes it's vector length.  */
+  rc = sem_wait (&vl_changed);
+  if (rc != 0)
+    {
+      perror ("sem_wait");
+      return 1;
+    }
+
+  rc = pthread_join (thread, NULL); /* break here 3 */
+  if (rc != 0)
+    {
+      perror ("pthread_join");
+      return 1;
+    }
+
+  return 0;
+}
diff --git a/gdb/testsuite/gdb.arch/aarch64-sve-threads.exp b/gdb/testsuite/gdb.arch/aarch64-sve-threads.exp
new file mode 100644
index 000000000000..48197650e1de
--- /dev/null
+++ b/gdb/testsuite/gdb.arch/aarch64-sve-threads.exp
@@ -0,0 +1,70 @@
+# Copyright 2023 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/>.
+
+# Test a multi-threaded binary that uses SVE and changes the SVE vector length
+# in the additional thread.
+
+if {[skip_aarch64_sve_tests]} {
+    verbose "Skipping ${gdb_test_file_name}."
+    return
+}
+
+standard_testfile
+if {[prepare_for_testing "failed to prepare" ${testfile} ${srcfile} \
+	 {debug pthreads}] == -1} {
+    return -1
+}
+
+if ![runto_main] {
+    return -1
+}
+
+# Stop after the additional thread has changed its vector length.
+gdb_breakpoint [gdb_get_line_number "break here 1"]
+gdb_continue_to_breakpoint "break here 1"
+
+# If GDB and gdbserver don't agree on the thread's vector length, this command
+# will fail.
+gdb_test "print \$z0" " = {q = {u = {.*}}}" "print z0 register"
+
+# Stop after the additional thread has restored its original vector length.
+gdb_breakpoint [gdb_get_line_number "break here 2"]
+gdb_continue_to_breakpoint "break here 2"
+
+# Test that going back to the original vector length doesn't confuse GDB or
+# gdbserver.
+gdb_test "print \$z0" " = {q = {u = {.*}}}" "print z0 register again"
+
+# Restart GDB to test a scenario where GDB switches to a thread that changed its
+# vector length but hasn't hit any breakpoints yet.
+clean_restart ${binfile}
+
+if ![runto_main] {
+    return -1
+}
+
+# Make the thread sleep after changing its vector length.
+gdb_test_no_output -nopass "set var should_sleep = 1" "make thread sleep"
+
+# Stop after the additional thread has been created.
+gdb_breakpoint [gdb_get_line_number "break here 3"]
+gdb_continue_to_breakpoint "break here 3"
+
+# The regexp accounts for two lines of output after the "Switching to thread" message.
+gdb_test_lines "thread 2" "switch to another thread" \
+    {\[Switching to thread 2 \(.*\)\]\r\n#0  [[:print:]]+}
+
+# Make sure everything is still fine.
+gdb_test "print \$z0" " = {q = {u = {.*}}}" "print z0 register in thread 2"