Re: Program-assigned thread names on Windows

LRN
2016-08-10T17:54:49Z

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On 10.08.2016 15:15, Pedro Alves wrote:
> On 08/10/2016 08:11 AM, LRN wrote:
>> No one seems to object.
>>
>
> I was going to apply your patches, so I squashed them all, and
> only after did I notice the problems, so I went ahead and did
> the changes. I also fixed a couple typos in the commit log.
>
> Could you give this updated patch a try? I build-tested it using
> a cross compiler, but haven't tried it out on Windows.

Curses! I've been reading your message like a set of last-minute nitpicks,
fixing things in my patch as i went along. I got to the named_thread->name
and overriding "thread name" part, then went ahead and fixed that too. Then
got to the end of the email and found out that you've done that already!
:-\ Good job, me...

Anyway, i've applied your patch. gdb compiles. threadname-setting
functionality works as expected: "thread name X" has precedence, "thread
name" (with no name) allows app-assigned name (if any) to be shown once again.

I've also applied my version of the patch. gdb also compiles.
threadname-setting functionality also works as expected. Therefore i'm
attaching my version, in case you find it useful.

I've only tested 32-bit version of gdb (hoping that none of the recent
changes touch anything architecture-dependent).

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From 34c05e6eb6e9d94700f8dc9695a214fdf6fabaea Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=D0=A0=D1=83=D1=81=D0=BB=D0=B0=D0=BD=20=D0=98=D0=B6=D0=B1?=
=?UTF-8?q?=D1=83=D0=BB=D0=B0=D1=82=D0=BE=D0=B2?= <lrn1986@gmail.com>
Date: Sun, 26 Jun 2016 11:14:49 +0000
Subject: [PATCH 1/3] Support settings thread name (MS-Windows)

This is done by catching an exception number 0x406D1388
(it has no documented name, though MSDN dubs it "MS_VC_EXCEPTION"
in one code example), which is thrown by the program.
The exception record contains an ID of a thread and a name to
give it.

This requires rolling back some changes in handle_exception(),
which now again returns more than two distinct values. The value
HANDLE_EXCEPTION_IGNORED means that gdb should just continue,
without returning thread ID up the stack (which will result
in further handling of the exception, which is not what we want).
---
gdb/windows-nat.c | 121 +++++++++++++++++++++++++++++++++++++++++++++++-------
1 file changed, 107 insertions(+), 14 deletions(-)

diff --git a/gdb/windows-nat.c b/gdb/windows-nat.c
index 3f67486..6315303 100644
--- a/gdb/windows-nat.c
+++ b/gdb/windows-nat.c
@@ -174,6 +174,18 @@ static int debug_registers_used;
static int windows_initialization_done;
#define DR6_CLEAR_VALUE 0xffff0ff0

+/* This exception has no documented name, but MSDN dubs it "MS_VC_EXCEPTION"
+ in one code example. It's thrown by a program to tell the debugger the name
+ of a thread. */
+#define MS_VC_EXCEPTION 0x406d1388
+
+typedef enum
+{
+ HANDLE_EXCEPTION_UNHANDLED = 0,
+ HANDLE_EXCEPTION_HANDLED,
+ HANDLE_EXCEPTION_IGNORED
+} handle_exception_result;
+
/* The string sent by cygwin when it processes a signal.
FIXME: This should be in a cygwin include file. */
#ifndef _CYGWIN_SIGNAL_STRING
@@ -441,6 +453,7 @@ windows_delete_thread (ptid_t ptid, DWORD exit_code)
{
windows_thread_info *here = th->next;
th->next = here->next;
+ xfree (here->name);
xfree (here);
}
}
@@ -1031,10 +1044,12 @@ display_selectors (char * args, int from_tty)
host_address_to_string (\
current_event.u.Exception.ExceptionRecord.ExceptionAddress))

-static int
+static handle_exception_result
handle_exception (struct target_waitstatus *ourstatus)
{
- DWORD code = current_event.u.Exception.ExceptionRecord.ExceptionCode;
+ EXCEPTION_RECORD *rec = &current_event.u.Exception.ExceptionRecord;
+ DWORD code = rec->ExceptionCode;
+ handle_exception_result result = HANDLE_EXCEPTION_HANDLED;

ourstatus->kind = TARGET_WAITKIND_STOPPED;

@@ -1057,14 +1072,13 @@ handle_exception (struct target_waitstatus *ourstatus)
cygwin-specific-signal. So, ignore SEGVs if they show up
within the text segment of the DLL itself. */
const char *fn;
- CORE_ADDR addr = (CORE_ADDR) (uintptr_t)
- current_event.u.Exception.ExceptionRecord.ExceptionAddress;
+ CORE_ADDR addr = (CORE_ADDR) (uintptr_t) rec->ExceptionAddress;

if ((!cygwin_exceptions && (addr >= cygwin_load_start
&& addr < cygwin_load_end))
|| (find_pc_partial_function (addr, &fn, NULL, NULL)
&& startswith (fn, "KERNEL32!IsBad")))
- return 0;
+ return HANDLE_EXCEPTION_UNHANDLED;
}
#endif
break;
@@ -1140,20 +1154,64 @@ handle_exception (struct target_waitstatus *ourstatus)
DEBUG_EXCEPTION_SIMPLE ("EXCEPTION_NONCONTINUABLE_EXCEPTION");
ourstatus->value.sig = GDB_SIGNAL_ILL;
break;
+ case MS_VC_EXCEPTION:
+ if (rec->NumberParameters >= 3
+ && (rec->ExceptionInformation[0] & 0xffffffff) == 0x1000)
+ {
+ long named_thread_id;
+ windows_thread_info *named_windows_thread;
+ CORE_ADDR thread_name_target;
+ char *thread_name;
+ int thread_name_len;
+
+ DEBUG_EXCEPTION_SIMPLE ("MS_VC_EXCEPTION");
+
+ named_thread_id = (long) (0xffffffff & rec->ExceptionInformation[2]);
+ thread_name_target = rec->ExceptionInformation[1];
+
+ if (named_thread_id == (DWORD) -1)
+ named_thread_id = current_event.dwThreadId;
+
+ named_windows_thread = thread_rec (named_thread_id, 0);
+
+ thread_name = NULL;
+ thread_name_len = 0;
+
+ if (named_windows_thread != NULL)
+ thread_name_len = target_read_string (thread_name_target,
+ &thread_name, 1025, 0);
+
+ if (thread_name_len > 0 && thread_name != NULL)
+ {
+ thread_name[thread_name_len - 1] = '\0';
+ if (thread_name[0] != '\0')
+ {
+ xfree (named_windows_thread->name);
+ named_windows_thread->name = thread_name;
+ }
+ else
+ {
+ xfree (thread_name);
+ }
+ }
+ ourstatus->value.sig = GDB_SIGNAL_TRAP;
+ result = HANDLE_EXCEPTION_IGNORED;
+ break;
+ }
+ /* treat improperly formed exception as unknown, fallthrough */
default:
/* Treat unhandled first chance exceptions specially. */
if (current_event.u.Exception.dwFirstChance)
- return 0;
+ return HANDLE_EXCEPTION_UNHANDLED;
printf_unfiltered ("gdb: unknown target exception 0x%08x at %s\n",
- (unsigned) current_event.u.Exception.ExceptionRecord.ExceptionCode,
- host_address_to_string (
- current_event.u.Exception.ExceptionRecord.ExceptionAddress));
+ (unsigned) rec->ExceptionCode,
+ host_address_to_string (rec->ExceptionAddress));
ourstatus->value.sig = GDB_SIGNAL_UNKNOWN;
break;
}
exception_count++;
last_sig = ourstatus->value.sig;
- return 1;
+ return result;
}

/* Resume thread specified by ID, or all artificially suspended
@@ -1510,10 +1568,19 @@ get_windows_debug_event (struct target_ops *ops,
"EXCEPTION_DEBUG_EVENT"));
if (saw_create != 1)
break;
- if (handle_exception (ourstatus))
- thread_id = current_event.dwThreadId;
- else
- continue_status = DBG_EXCEPTION_NOT_HANDLED;
+ switch (handle_exception (ourstatus))
+ {
+ case HANDLE_EXCEPTION_UNHANDLED:
+ default:
+ continue_status = DBG_EXCEPTION_NOT_HANDLED;
+ break;
+ case HANDLE_EXCEPTION_HANDLED:
+ thread_id = current_event.dwThreadId;
+ break;
+ case HANDLE_EXCEPTION_IGNORED:
+ continue_status = DBG_CONTINUE;
+ break;
+ }
break;

case OUTPUT_DEBUG_STRING_EVENT: /* Message from the kernel. */
@@ -2514,6 +2581,31 @@ windows_get_ada_task_ptid (struct target_ops *self, long lwp, long thread)
return ptid_build (ptid_get_pid (inferior_ptid), 0, lwp);
}

+static const char *
+windows_get_thread_name (struct target_ops *self, struct thread_info *thr)
+{
+ struct thread_info *threadinfo;
+ windows_thread_info *windows_threadinfo;
+ DWORD id = ptid_get_tid (thr->ptid);
+ char *name;
+
+ name = NULL;
+ threadinfo = find_thread_ptid (thr->ptid);
+
+ if (threadinfo != NULL)
+ name = threadinfo->name;
+
+ if (name == NULL && id != 0)
+ {
+ windows_threadinfo = thread_rec (id, 0);
+
+ if (windows_threadinfo != NULL)
+ name = windows_threadinfo->name;
+ }
+
+ return (const char *) name;
+}
+
static struct target_ops *
windows_target (void)
{
@@ -2538,6 +2630,7 @@ windows_target (void)
t->to_pid_to_exec_file = windows_pid_to_exec_file;
t->to_get_ada_task_ptid = windows_get_ada_task_ptid;
t->to_get_tib_address = windows_get_tib_address;
+ t->to_thread_name = windows_get_thread_name;

return t;
}
--
2.4.0

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