Add test for stepping over clone syscall

- New in v3:

  Addressed issue Tom de Vries ran into with no debug info for glibc.

- New in v2:

  Fixed race, remove end anchor after prompt.

  Fix leading anchor and inferior output flushing issue against
  gdbserver.

  Now works with displaced stepping.

  Avoid printing inferior addresses in gdb.sum messages

  Fail when clone child thread is stuck on scratchpad

  Misc minor tweaks throughout.

This adds a new gdb.threads/stepi-over-clone.exp testcase, which
exercises stepping over a clone syscall, with displaced stepping vs
inline stepping, and all-stop vs non-stop.  We already test stepping
over clone syscalls with gdb.base/step-over-syscall.exp, but this test
uses pthreads, while the other test uses raw clone, and this one is
more thorough.

Co-authored-by: Pedro Alves <pedro@palves.net>
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=19675
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=27830
Change-Id: I95c06024736384ae8542a67ed9fdf6534c325c8e

2 files changed, 482 insertions, 0 deletions

diff --git a/gdb/testsuite/gdb.threads/stepi-over-clone.c b/gdb/testsuite/gdb.threads/stepi-over-clone.c
new file mode 100644
index 0000000..580cf2d
--- /dev/null
+++ b/gdb/testsuite/gdb.threads/stepi-over-clone.c
@@ -0,0 +1,90 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2021-2022 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 <stdio.h>
+#include <pthread.h>
+#include <unistd.h>
+#include <signal.h>
+#include <stdlib.h>
+
+/* Set this to non-zero from GDB to start a third worker thread.  */
+volatile int start_third_thread = 0;
+
+void *
+thread_worker_2 (void *arg)
+{
+  int i;
+
+  printf ("Hello from the third thread.\n");
+  fflush (stdout);
+
+  for (i = 0; i < 300; ++i)
+    sleep (1);
+
+  return NULL;
+}
+
+void *
+thread_worker_1 (void *arg)
+{
+  int i;
+  pthread_t thr;
+  void *val;
+
+  if (start_third_thread)
+    pthread_create (&thr, NULL, thread_worker_2, NULL);
+
+  printf ("Hello from the first thread.\n");
+  fflush (stdout);
+
+  for (i = 0; i < 300; ++i)
+    sleep (1);
+
+  if (start_third_thread)
+    pthread_join (thr, &val);
+
+  return NULL;
+}
+
+void *
+thread_idle_loop (void *arg)
+{
+  int i;
+
+  for (i = 0; i < 300; ++i)
+    sleep (1);
+
+  return NULL;
+}
+
+int
+main ()
+{
+  pthread_t thr, thr_idle;
+  void *val;
+
+  if (getenv ("MAKE_EXTRA_THREAD") != NULL)
+    pthread_create (&thr_idle, NULL, thread_idle_loop, NULL);
+
+  pthread_create (&thr, NULL, thread_worker_1, NULL);
+  pthread_join (thr, &val);
+
+  if (getenv ("MAKE_EXTRA_THREAD") != NULL)
+    pthread_join (thr_idle, &val);
+
+  return 0;
+}
diff --git a/gdb/testsuite/gdb.threads/stepi-over-clone.exp b/gdb/testsuite/gdb.threads/stepi-over-clone.exp
new file mode 100644
index 0000000..d9cbe2b
--- /dev/null
+++ b/gdb/testsuite/gdb.threads/stepi-over-clone.exp
@@ -0,0 +1,392 @@
+# Copyright 2021-2022 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/>.
+
+# Test performing a 'stepi' over a clone syscall instruction.
+
+# This test relies on us being able to spot syscall instructions in
+# disassembly output.  For now this is only implemented for x86-64.
+if { ![istarget x86_64-*-* ] } {
+    return
+}
+
+standard_testfile
+
+if { [prepare_for_testing "failed to prepare" $testfile $srcfile \
+	  {debug pthreads additional_flags=-static}] } {
+    return
+}
+
+if {![runto_main]} {
+    return
+}
+
+# Arrange to catch the 'clone' syscall, run until we catch the
+# syscall, and try to figure out the address of the actual syscall
+# instruction so we can place a breakpoint at this address.
+
+gdb_test_multiple "catch syscall clone" "" {
+    -re "The feature \'catch syscall\' is not supported.*\r\n$gdb_prompt $" {
+	set supported 0
+	pass $gdb_test_name
+	return
+    }
+    -re ".*$gdb_prompt $" {
+	pass $gdb_test_name
+    }
+}
+
+gdb_test "continue" \
+    "Catchpoint $decimal \\(call to syscall clone\\), .*"
+
+# Return true if INSN is a syscall instruction.
+
+proc is_syscall_insn { insn } {
+    if [istarget x86_64-*-* ] {
+	return { $insn == "syscall" }
+    } else {
+	error "port me"
+    }
+}
+
+# A list of addresses with syscall instructions.
+set syscall_addrs {}
+
+# Get list of addresses with syscall instructions.
+gdb_test_multiple "disassemble" "" {
+    -re "Dump of assembler code for function \[^\r\n\]+:\r\n" {
+	exp_continue
+    }
+    -re "^(?:=>)?\\s+(${hex})\\s+<\\+${decimal}>:\\s+(\[^\r\n\]+)\r\n" {
+	set addr $expect_out(1,string)
+	set insn [string trim $expect_out(2,string)]
+	if [is_syscall_insn $insn] {
+	    verbose -log "Found a syscall at: $addr"
+	    lappend syscall_addrs $addr
+	}
+	exp_continue
+    }
+    -re "^End of assembler dump\\.\r\n$gdb_prompt $" {
+	if { [llength $syscall_addrs] == 0 } {
+	    unsupported "no syscalls found"
+	    return -1
+	}
+    }
+}
+
+# The test proc.  NON_STOP and DISPLACED are either 'on' or 'off', and are
+# used to configure how GDB starts up.  THIRD_THREAD is either true or false,
+# and is used to configure the inferior.
+proc test {non_stop displaced third_thread} {
+    global binfile srcfile
+    global syscall_addrs
+    global GDBFLAGS
+    global gdb_prompt hex decimal
+
+    for { set i 0 } { $i < 3 } { incr i } {
+	with_test_prefix "i=$i" {
+
+	    # Arrange to start GDB in the correct mode.
+	    save_vars { GDBFLAGS } {
+		append GDBFLAGS " -ex \"set non-stop $non_stop\""
+		append GDBFLAGS " -ex \"set displaced $displaced\""
+		clean_restart $binfile
+	    }
+
+	    runto_main
+
+	    # Setup breakpoints at all the syscall instructions we
+	    # might hit.  Only issue one pass/fail to make tests more
+	    # comparable between systems.
+	    set test "break at syscall insns"
+	    foreach addr $syscall_addrs {
+		if {[gdb_test -nopass "break *$addr" \
+			 ".*" \
+			 $test] != 0} {
+		    return
+		}
+	    }
+	    # If we got here, all breakpoints were set successfully.
+	    # We used -nopass above, so issue a pass now.
+	    pass $test
+
+	    # Continue until we hit the syscall.
+	    gdb_test "continue"
+
+	    if { $third_thread } {
+		gdb_test_no_output "set start_third_thread=1"
+	    }
+
+	    set stepi_error_count 0
+	    set stepi_new_thread_count 0
+	    set thread_1_stopped false
+	    set thread_2_stopped false
+	    set seen_prompt false
+	    set hello_first_thread false
+
+	    # The program is now stopped at main, but if testing
+	    # against GDBserver, inferior_spawn_id is GDBserver's
+	    # spawn_id, and the GDBserver output emitted before the
+	    # program stopped isn't flushed unless we explicitly do
+	    # so, because it is on a different spawn_id.  We could try
+	    # flushing it now, to avoid confusing the following tests,
+	    # but that would have to be done under a timeout, and
+	    # would thus slow down the testcase.  Instead, if inferior
+	    # output goes to a different spawn id, then we don't need
+	    # to wait for the first message from the inferior with an
+	    # anchor, as we know consuming inferior output won't
+	    # consume GDB output.  OTOH, if inferior output is coming
+	    # out on GDB's terminal, then we must use an anchor,
+	    # otherwise matching inferior output without one could
+	    # consume GDB output that we are waiting for in regular
+	    # expressions that are written after the inferior output
+	    # regular expression match.
+	    if {$::inferior_spawn_id != $::gdb_spawn_id} {
+		set anchor ""
+	    } else {
+		set anchor "^"
+	    }
+
+	    gdb_test_multiple "stepi" "" {
+		-re "^stepi\r\n" {
+		    verbose -log "XXX: Consume the initial command"
+		    exp_continue
+		}
+		-re "^\\\[New Thread\[^\r\n\]+\\\]\r\n" {
+		    verbose -log "XXX: Consume new thread line"
+		    incr stepi_new_thread_count
+		    exp_continue
+		}
+		-re "^\\\[Switching to Thread\[^\r\n\]+\\\]\r\n" {
+		    verbose -log "XXX: Consume switching to thread line"
+		    exp_continue
+		}
+		-re "^\\s*\r\n" {
+		    verbose -log "XXX: Consume blank line"
+		    exp_continue
+		}
+
+		-i $::inferior_spawn_id
+
+		-re "${anchor}Hello from the first thread\\.\r\n" {
+		    set hello_first_thread true
+
+		    verbose -log "XXX: Consume first worker thread message"
+		    if { $third_thread } {
+			# If we are going to start a third thread then GDB
+			# should hit the breakpoint in clone before printing
+			# this message.
+			incr stepi_error_count
+		    }
+		    if { !$seen_prompt } {
+			exp_continue
+		    }
+		}
+		-re "^Hello from the third thread\\.\r\n" {
+		    # We should never see this message.
+		    verbose -log "XXX: Consume third worker thread message"
+		    incr stepi_error_count
+		    if { !$seen_prompt } {
+			exp_continue
+		    }
+		}
+
+		-i $::gdb_spawn_id
+
+		-re "^$hex in clone \\(\\)\r\n" {
+		    verbose -log "XXX: Consume stop location line"
+		    set thread_1_stopped true
+		    if { !$seen_prompt } {
+			verbose -log "XXX: Continuing to look for the prompt"
+			exp_continue
+		    }
+		}
+		-re "^$gdb_prompt " {
+		    verbose -log "XXX: Consume the final prompt"
+		    gdb_assert { $stepi_error_count == 0 }
+		    gdb_assert { $stepi_new_thread_count == 1 }
+		    set seen_prompt true
+		    if { $third_thread } {
+			if { $non_stop } {
+			    # In non-stop mode if we are trying to start a
+			    # third thread (from the second thread), then the
+			    # second thread should hit the breakpoint in clone
+			    # before actually starting the third thread.  And
+			    # so, at this point both thread 1, and thread 2
+			    # should now be stopped.
+			    if { !$thread_1_stopped || !$thread_2_stopped } {
+				verbose -log "XXX: Continue looking for an additional stop event"
+				exp_continue
+			    }
+			} else {
+			    # All stop mode.  Something should have stoppped
+			    # by now otherwise we shouldn't have a prompt, but
+			    # we can't know which thread will have stopped as
+			    # that is a race condition.
+			    gdb_assert { $thread_1_stopped || $thread_2_stopped }
+			}
+		    }
+
+		    if {$non_stop && !$hello_first_thread} {
+			exp_continue
+		    }
+
+		}
+		-re "^Thread 2\[^\r\n\]+ hit Breakpoint $decimal, $hex in clone \\(\\)\r\n" {
+		    verbose -log "XXX: Consume thread 2 hit breakpoint"
+		    set thread_2_stopped true
+		    if { !$seen_prompt } {
+			verbose -log "XXX: Continuing to look for the prompt"
+			exp_continue
+		    }
+		}
+		-re "^PC register is not available\r\n" {
+		    # This is the error we'd see for remote targets.
+		    verbose -log "XXX: Consume error line"
+		    incr stepi_error_count
+		    exp_continue
+		}
+		-re "^Couldn't get registers: No such process\\.\r\n" {
+		    # This is the error we see'd for native linux
+		    # targets.
+		    verbose -log "XXX: Consume error line"
+		    incr stepi_error_count
+		    exp_continue
+		}
+	    }
+
+	    # Ensure we are back at a GDB prompt, resynchronise.
+	    verbose -log "XXX: Have completed scanning the 'stepi' output"
+	    gdb_test "p 1 + 2 + 3" " = 6"
+
+	    # Check the number of threads we have, it should be exactly two.
+	    set thread_count 0
+	    set bad_threads 0
+
+	    # Build up our expectations for what the current thread state
+	    # should be.  Thread 1 is the easiest, this is the thread we are
+	    # stepping, so this thread should always be stopped, and should
+	    # always still be in clone.
+	    set match_code {}
+	    lappend match_code {
+		-re "\\*?\\s+1\\s+Thread\[^\r\n\]+clone \\(\\)\r\n" {
+		    incr thread_count
+		    exp_continue
+		}
+	    }
+
+	    # What state should thread 2 be in?
+	    if { $non_stop == "on" } {
+		if { $third_thread } {
+		    # With non-stop mode on, and creation of a third thread
+		    # having been requested, we expect Thread 2 to exist, and
+		    # be stopped at the breakpoint in clone (just before the
+		    # third thread is actually created).
+		    lappend match_code {
+			-re "\\*?\\s+2\\s+Thread\[^\r\n\]+$hex in clone \\(\\)\r\n" {
+			    incr thread_count
+			    exp_continue
+			}
+			-re "\\*?\\s+2\\s+Thread\[^\r\n\]+\\(running\\)\r\n" {
+			    incr thread_count
+			    incr bad_threads
+			    exp_continue
+			}
+			-re "\\*?\\s+2\\s+Thread\[^\r\n\]+\r\n" {
+			    verbose -log "XXX: thread 2 is bad, unknown state"
+			    incr thread_count
+			    incr bad_threads
+			    exp_continue
+			}
+		    }
+
+		} else {
+		    # With non-stop mode on, and no third thread having been
+		    # requested, then we expect Thread 2 to exist, and still
+		    # be running.
+		    lappend match_code {
+			-re "\\*?\\s+2\\s+Thread\[^\r\n\]+\\(running\\)\r\n" {
+			    incr thread_count
+			    exp_continue
+			}
+			-re "\\*?\\s+2\\s+Thread\[^\r\n\]+\r\n" {
+			    verbose -log "XXX: thread 2 is bad, unknown state"
+			    incr thread_count
+			    incr bad_threads
+			    exp_continue
+			}
+		    }
+		}
+	    } else {
+		# With non-stop mode off then we expect Thread 2 to exist, and
+		# be stopped.  We don't have any guarantee about where the
+		# thread will have stopped though, so we need to be vague.
+		lappend match_code {
+		    -re "\\*?\\s+2\\s+Thread\[^\r\n\]+\\(running\\)\r\n" {
+			verbose -log "XXX: thread 2 is bad, unexpectedly running"
+			incr thread_count
+			incr bad_threads
+			exp_continue
+		    }
+		    -re "\\*?\\s+2\\s+Thread\[^\r\n\]+_start\[^\r\n\]+\r\n" {
+			# We know that the thread shouldn't be stopped
+			# at _start, though.  This is the location of
+			# the scratch pad on Linux at the time of
+			# writting.
+			verbose -log "XXX: thread 2 is bad, stuck in scratchpad"
+			incr thread_count
+			incr bad_threads
+			exp_continue
+		    }
+		    -re "\\*?\\s+2\\s+Thread\[^\r\n\]+\r\n" {
+			incr thread_count
+			exp_continue
+		    }
+		}
+	    }
+
+	    # We don't expect to ever see a thread 3.  Even when we are
+	    # requesting that this third thread be created, thread 2, the
+	    # thread that creates thread 3, should stop before executing the
+	    # clone syscall.  So, if we do ever see this then something has
+	    # gone wrong.
+	    lappend match_code {
+		-re "\\s+3\\s+Thread\[^\r\n\]+\r\n" {
+		    incr thread_count
+		    incr bad_threads
+		    exp_continue
+		}
+	    }
+
+	    lappend match_code {
+		-re "$gdb_prompt $" {
+		    gdb_assert { $thread_count == 2 }
+		    gdb_assert { $bad_threads == 0 }
+		}
+	    }
+
+	    set match_code [join $match_code]
+	    gdb_test_multiple "info threads" "" $match_code
+	}
+    }
+}
+
+# Run the test in all suitable configurations.
+foreach_with_prefix third_thread { false true } {
+    foreach_with_prefix non-stop { "on" "off" } {
+	foreach_with_prefix displaced { "off" "on" } {
+	    test ${non-stop} ${displaced} ${third_thread}
+	}
+    }
+}