Re: Program-assigned thread names on Windows

Jon Turney
2016-07-25T12:17:54Z

On 23/07/2016 18:01, LRN wrote:
> On 23.07.2016 19:39, John Baldwin wrote:
>> > On Saturday, July 23, 2016 12:25:15 PM LRN wrote:
>>> >> The attached patch adds thread naming support on Windows.

Nice. A few comments below.

>>> >>
>>> >> This works as documented[1] on MSDN - by catching a specific
>>> >> exception that the program throws.
>>> >>
>>> >> Setting thread name this way is supported by glib[2] and winpthreads[3]
>>> >> at least, as well as any program developed with MS toolchain (because
>>> >> WinDbg supported this for a long time).
>>> >>
>>> >> [1] https://msdn.microsoft.com/en-us/library/xcb2z8hs.aspx
>>> >> [2] https://git.gnome.org/browse/glib/commit/glib
>>> >> /gthread-win32.c?id=e118856430a798bbc529691ad235fd0b0684439d
>>> >> [3] https://sourceforge.net/p/mingw-w64/mingw-w64/ci
>>> >> /0d95c795b44b76e1b60dfc119fd93cfd0cb35816/
>> >
>
> This is done by catching an exception number 0x406D1388
> (it has no documented name), which is thrown by the program.

The name used in the MSDN article [1] is 'MS_VC_EXCEPTION', so why not
use that?

> + case WINDOWS_THREADNAME_EXCEPTION:
> + DEBUG_EXCEPTION_SIMPLE (WINDOWS_THREADNAME_EXCEPTION_S);
> + ourstatus->value.sig = GDB_SIGNAL_TRAP;
> + if (current_event.u.Exception.ExceptionRecord.NumberParameters == 4)
> + {
> + DWORD named_thread_id;
> + ptid_t named_thread_ptid;
> + struct thread_info *named_thread;
> + uintptr_t thread_name_target;
> + char *thread_name;
> +

Shouldn't this check for ExceptionInformation[0] = 0x1000, and treat
this as an unknown exception otherwise?

> + named_thread_id = (DWORD) current_event.u.Exception.ExceptionRecord.ExceptionInformation[2];
> + thread_name_target = (uintptr_t) current_event.u.Exception.ExceptionRecord.ExceptionInformation[1];

Is this going to be correct for 64-bit builds?

> +
> + if (named_thread_id == (DWORD) -1)
> + named_thread_id = current_event.dwThreadId;
> +
> + named_thread_ptid = ptid_build (current_event.dwProcessId, 0, named_thread_id),
> + named_thread = find_thread_ptid (named_thread_ptid);
> +
> + thread_name = NULL;
> + if (target_read_string ((CORE_ADDR) thread_name_target, &thread_name, 1024, 0))

Does thread_name end up not being null terminated if the thread name
length really exceeds 1024? (or is improperly not null terminated in the
target process...)

> + {
> + if (thread_name != NULL && thread_name[0] != '\0')
> + {
> + xfree (named_thread->name);
> + named_thread->name = thread_name;
> + }
> + else if (thread_name != NULL)
> + {
> + /* nothing to do */;
> + xfree (thread_name);
> + }
> + }
> + result = 2;
> + }
> + break;
> default:
> /* Treat unhandled first chance exceptions specially. */
> if (current_event.u.Exception.dwFirstChance)
> @@ -1153,7 +1194,7 @@ handle_exception (struct target_waitstatus *ourstatus)
> }
> exception_count++;
> last_sig = ourstatus->value.sig;
> - return 1;
> + return result;
> }
>
> /* Resume thread specified by ID, or all artificially suspended
> @@ -1510,10 +1551,19 @@ 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 0:
> + default:
> + continue_status = DBG_EXCEPTION_NOT_HANDLED;
> + break;
> + case 1:
> + thread_id = current_event.dwThreadId;
> + break;
> + case 2:
> + continue_status = DBG_CONTINUE;
> + break;
> + }
> break;
>
> case OUTPUT_DEBUG_STRING_EVENT: /* Message from the kernel. */
> -- 2.4.0
>