Re: Regression: GDB stopped on run with attached process (PR 17347) [Re: [pushed+7.8] Re: [PATCH] Fix "attach" command vs user input race

Pedro Alves
2014-09-03T20:11:11Z

On 09/03/2014 08:58 AM, Jan Kratochvil wrote:

> https://sourceware.org/bugzilla/show_bug.cgi?id=17347

Thanks Jan.

Here's a fix, test included. Comments?

Thanks,
Pedro Alves

--------------------------
[PATCH] gdb/17347 - Regression: GDB stopped on run with attached process

Doing:

gdb --pid=PID -ex run

Results in GDB getting a SIGTTIN, and thus ending stopped. That's
usually indicative of a missing target_terminal_ours call.

E.g., from the PR:

$ sleep 1h & p=$!; sleep 0.1; gdb -batch sleep $p -ex run
[1] 28263
[1] Killed sleep 1h

[2]+ Stopped gdb -batch sleep $p -ex run

The workaround is doing:

gdb -ex "attach $PID" -ex "run"

instead of

gdb [-p] $PID -ex "run"

With the former, gdb waits for the attach command to complete before
moving on to the "run" command, because the interpreter is in sync
mode at this point, within execute_command. But for the latter,
attach_command is called directly from captured_main, and thus misses
that waiting. IOW, "run" is running before the attach continuation
has run, before the program stops and attach completes. The broken
terminal settings are just one symptom of that. Any command that
queries or requires input results in the same.

The fix is to wait in catch_command_errors (which is specific to
main.c nowadays), just like we wait in execute_command.

gdb/ChangeLog:
2014-09-03 Pedro Alves <palves@redhat.com>

PR gdb/17347
* main.c: Include "infrun.h".
(catch_command_errors, catch_command_errors_const): Wait for the
foreground command to complete.
* top.c (maybe_wait_sync_command_done): New function, factored out
from ...
(maybe_wait_sync_command_done): ... here.
* top.h (maybe_wait_sync_command_done): New declaration.

gdb/testsuite/ChangeLog:
2014-09-03 Pedro Alves <palves@redhat.com>

PR gdb/17347
* gdb.base/attach.exp (spawn_test_prog): New, factored out from
...
(do_attach_tests, do_call_attach_tests, do_command_attach_tests):
... here.
(gdb_spawn_with_cmdline_opts): New procedure.
(test_command_line_attach_run): New procedure.
(top level): Call it.
---
gdb/main.c | 9 +++
gdb/testsuite/gdb.base/attach.exp | 118 ++++++++++++++++++++++++++------------
gdb/top.c | 26 +++++----
gdb/top.h | 8 +++
4 files changed, 114 insertions(+), 47 deletions(-)

diff --git a/gdb/main.c b/gdb/main.c
index 12f0146..756dd4f 100644
--- a/gdb/main.c
+++ b/gdb/main.c
@@ -45,6 +45,7 @@
#include "filestuff.h"
#include <signal.h>
#include "event-top.h"
+#include "infrun.h"

/* The selected interpreter. This will be used as a set command
variable, so it should always be malloc'ed - since
@@ -369,7 +370,11 @@ catch_command_errors (catch_command_errors_ftype *command,

TRY_CATCH (e, mask)
{
+ int was_sync = sync_execution;
+
command (arg, from_tty);
+
+ maybe_wait_sync_command_done (was_sync);
}
return handle_command_errors (e);
}
@@ -388,7 +393,11 @@ catch_command_errors_const (catch_command_errors_const_ftype *command,

TRY_CATCH (e, mask)
{
+ int was_sync = sync_execution;
+
command (arg, from_tty);
+
+ maybe_wait_sync_command_done (was_sync);
}
return handle_command_errors (e);
}
diff --git a/gdb/testsuite/gdb.base/attach.exp b/gdb/testsuite/gdb.base/attach.exp
index 9714c29..c94c127 100644
--- a/gdb/testsuite/gdb.base/attach.exp
+++ b/gdb/testsuite/gdb.base/attach.exp
@@ -58,6 +58,37 @@ if [get_compiler_info] {
return -1
}

+# Start the program running and then wait for a bit, to be sure that
+# it can be attached to. Return the process's PID.
+
+proc spawn_test_prog { executable } {
+ set testpid [eval exec $executable &]
+ exec sleep 2
+ if { [istarget "*-*-cygwin*"] } {
+ # testpid is the Cygwin PID, GDB uses the Windows PID, which might be
+ # different due to the way fork/exec works.
+ set testpid [ exec ps -e | gawk "{ if (\$1 == $testpid) print \$4; }" ]
+ }
+
+ return $testpid
+}
+
+# Spawn GDB with CMDLINE_FLAGS appended to the GDBFLAGS global.
+
+proc gdb_spawn_with_cmdline_opts { cmdline_flags } {
+ global GDBFLAGS
+
+ set saved_gdbflags $GDBFLAGS
+
+ append GDBFLAGS $cmdline_flags
+
+ set res [gdb_spawn]
+
+ set GDBFLAGS $saved_gdbflags
+
+ return $res
+}
+
proc do_attach_tests {} {
global gdb_prompt
global binfile
@@ -70,13 +101,7 @@ proc do_attach_tests {} {
# Start the program running and then wait for a bit, to be sure
# that it can be attached to.

- set testpid [eval exec $binfile &]
- exec sleep 2
- if { [istarget "*-*-cygwin*"] } {
- # testpid is the Cygwin PID, GDB uses the Windows PID, which might be
- # different due to the way fork/exec works.
- set testpid [ exec ps -e | gawk "{ if (\$1 == $testpid) print \$4; }" ]
- }
+ set testpid [spawn_test_prog $binfile]

# Verify that we cannot attach to nonsense.

@@ -279,16 +304,7 @@ proc do_attach_tests {} {

remote_exec build "kill -9 ${testpid}"

- # Start the program running and then wait for a bit, to be sure
- # that it can be attached to.
-
- set testpid [eval exec $binfile &]
- exec sleep 2
- if { [istarget "*-*-cygwin*"] } {
- # testpid is the Cygwin PID, GDB uses the Windows PID, which might be
- # different due to the way fork/exec works.
- set testpid [ exec ps -e | gawk "{ if (\$1 == $testpid) print \$4; }" ]
- }
+ set testpid [spawn_test_prog $binfile]

# Verify that we can attach to the process, and find its a.out
# when we're cd'd to some directory that doesn't contain the
@@ -335,16 +351,7 @@ proc do_call_attach_tests {} {
global gdb_prompt
global binfile2

- # Start the program running and then wait for a bit, to be sure
- # that it can be attached to.
-
- set testpid [eval exec $binfile2 &]
- exec sleep 2
- if { [istarget "*-*-cygwin*"] } {
- # testpid is the Cygwin PID, GDB uses the Windows PID, which might be
- # different due to the way fork/exec works.
- set testpid [ exec ps -e | gawk "{ if (\$1 == $testpid) print \$4; }" ]
- }
+ set testpid [spawn_test_prog $binfile2]

# Attach

@@ -397,16 +404,7 @@ proc do_command_attach_tests {} {
return 0
}

- # Start the program running and then wait for a bit, to be sure
- # that it can be attached to.
-
- set testpid [eval exec $binfile &]
- exec sleep 2
- if { [istarget "*-*-cygwin*"] } {
- # testpid is the Cygwin PID, GDB uses the Windows PID, which might be
- # different due to the way fork/exec works.
- set testpid [ exec ps -e | gawk "{ if (\$1 == $testpid) print \$4; }" ]
- }
+ set testpid [spawn_test_prog $binfile]

gdb_exit
if $verbose>1 then {
@@ -429,6 +427,50 @@ proc do_command_attach_tests {} {
remote_exec build "kill -9 ${testpid}"
}

+# Test ' gdb --pid PID -ex "run" '. GDB used to have a bug where
+# "run" would run before the attach finished - PR17347.
+
+proc test_command_line_attach_run {} {
+ global gdb_prompt
+ global binfile
+ global verbose
+ global GDB
+ global INTERNAL_GDBFLAGS
+
+ if ![isnative] then {
+ unsupported "commandline attach run test"
+ return 0
+ }
+
+ with_test_prefix "cmdline attach run" {
+ set testpid [spawn_test_prog $binfile]
+
+ set test "run to prompt"
+ gdb_exit
+ set res [gdb_spawn_with_cmdline_opts "--pid=$testpid -ex \"start\""]
+ if { $res != 0} {
+ fail $test
+ return $res
+ }
+ gdb_test_multiple "" $test {
+ -re {Attaching to.*Start it from the beginning\? \(y or n\) } {
+ pass $test
+ }
+ }
+
+ send_gdb "y\n"
+
+ set test "run to main"
+ gdb_test_multiple "" $test {
+ -re "Temporary breakpoint .* main .*$gdb_prompt $" {
+ pass $test
+ }
+ }
+
+ # Get rid of the process
+ remote_exec build "kill -9 ${testpid}"
+ }
+}

# Start with a fresh gdb

@@ -453,4 +495,6 @@ do_call_attach_tests

do_command_attach_tests

+test_command_line_attach_run
+
return 0
diff --git a/gdb/top.c b/gdb/top.c
index fc2b84d..ba71f8f 100644
--- a/gdb/top.c
+++ b/gdb/top.c
@@ -373,6 +373,21 @@ check_frame_language_change (void)
}
}

+void
+maybe_wait_sync_command_done (int was_sync)
+{
+ /* If the interpreter is in sync mode (we're running a user
+ command's list, running command hooks or similars), and we
+ just ran a synchronous command that started the target, wait
+ for that command to end. */
+ if (!interpreter_async && !was_sync && sync_execution)
+ {
+ while (gdb_do_one_event () >= 0)
+ if (!sync_execution)
+ break;
+ }
+}
+
/* Execute the line P as a command, in the current user context.
Pass FROM_TTY as second argument to the defining function. */

@@ -459,16 +474,7 @@ execute_command (char *p, int from_tty)
else
cmd_func (c, arg, from_tty);

- /* If the interpreter is in sync mode (we're running a user
- command's list, running command hooks or similars), and we
- just ran a synchronous command that started the target, wait
- for that command to end. */
- if (!interpreter_async && !was_sync && sync_execution)
- {
- while (gdb_do_one_event () >= 0)
- if (!sync_execution)
- break;
- }
+ maybe_wait_sync_command_done (was_sync);

/* If this command has been post-hooked, run the hook last. */
execute_cmd_post_hook (c);
diff --git a/gdb/top.h b/gdb/top.h
index c322c33..94f6c48 100644
--- a/gdb/top.h
+++ b/gdb/top.h
@@ -42,6 +42,14 @@ extern void quit_command (char *, int);
extern void quit_cover (void);
extern void execute_command (char *, int);

+/* If the interpreter is in sync mode (we're running a user command's
+ list, running command hooks or similars), and we just ran a
+ synchronous command that started the target, wait for that command
+ to end. WAS_SYNC indicates whether sync_execution was set before
+ the command was run. */
+
+extern void maybe_wait_sync_command_done (int was_sync);
+
extern void check_frame_language_change (void);

/* Prepare for execution of a command.
--
1.9.3