Re: make attaching to stopped processes work under windows

[Oswald Buddenhagen <oswald dot buddenhagen at trolltech dot de>]

On Sun, Mar 08, 2009 at 03:32:33PM -0400, Christopher Faylor wrote:
> On Tue, Mar 03, 2009 at 01:05:04PM +0100, Oswald Buddenhagen wrote:
> >after all, why should it matter
> >whether the process is suspended in the first place?
> 
> Because you may be debugging a situation where you want precise control
> over the process's suspend count.  The process may be suspended for
> reasons other than the way that you are specifically using it.
> 
the bad news is that gdb simply hangs without my patch, so your
situation is rather hypothetical.
i guess the right fix (if at all possible) would be making it not hang
and resume the thread from the outside once gdb reports success. but
investigating that is way beyond what my employer is likely willing to
pay for.
if you feel like debugging it, just compile the attachment and run it
like

  process_stub_win debug <somefile> "" "" notepad "press enter..."

then read the pid from <somefile> and use it to attach gdb.

> This would mean that you'd need to have an assignment on file with the
> FSF so if you are willing to pursue that alternative it would make
> sense to start that process ASAP.
> 
i'm covered, the process is rolling (or rather, crawling uphill) for a
few months now ...

/***************************************************************************
**
** This file is part of Qt Creator
**
** Copyright (c) 2008-2009 Nokia Corporation and/or its subsidiary(-ies).
**
** Contact:  Qt Software Information (qt-info@nokia.com)
**
**
** Non-Open Source Usage
**
** Licensees may use this file in accordance with the Qt Beta Version
** License Agreement, Agreement version 2.2 provided with the Software or,
** alternatively, in accordance with the terms contained in a written
** agreement between you and Nokia.
**
** GNU General Public License Usage
**
** Alternatively, this file may be used under the terms of the GNU General
** Public License versions 2.0 or 3.0 as published by the Free Software
** Foundation and appearing in the file LICENSE.GPL included in the packaging
** of this file.  Please review the following information to ensure GNU
** General Public Licensing requirements will be met:
**
** http://www.fsf.org/licensing/licenses/info/GPLv2.html and
** http://www.gnu.org/copyleft/gpl.html.
**
** In addition, as a special exception, Nokia gives you certain additional
** rights. These rights are described in the Nokia Qt GPL Exception
** version 1.3, included in the file GPL_EXCEPTION.txt in this package.
**
***************************************************************************/

#define _WIN32_WINNT 0x0501 /* WinXP, needed for DebugActiveProcessStop() */

#include <windows.h>
#include <string.h>
#include <stdio.h>
#include <errno.h>
#include <direct.h>

static FILE *qtcFd;
static wchar_t *sleepMsg;

/* Print some "press enter" message, wait for that, exit. */
static void doExit(int code)
{
    char buf[2];
    _putws(sleepMsg);
    fgets(buf, 2, stdin); /* Minimal size to make it wait */
    exit(code);
}

/* Print an error message for unexpected Windows system errors, wait, exit. */
static void systemError(const char *str)
{
    fprintf(stderr, str, GetLastError());
    doExit(3);
}

/* Send a message to the master. */
static void sendMsg(const char *msg, int num)
{
    int pidStrLen;
    char pidStr[64];

    pidStrLen = sprintf(pidStr, msg, num);
    if (fwrite(pidStr, pidStrLen, 1, qtcFd) != 1 || fflush(qtcFd)) {
        fprintf(stderr, "Cannot write to creator comm socket: %s\n",
                strerror(errno));
        doExit(3);
    }
}

/* Ignore the first ctrl-c/break within a second. */
static BOOL WINAPI ctrlHandler(DWORD dwCtrlType)
{
    static ULARGE_INTEGER lastTime;
    ULARGE_INTEGER thisTime;
    SYSTEMTIME sysTime;
    FILETIME fileTime;

    if (dwCtrlType == CTRL_C_EVENT || dwCtrlType == CTRL_BREAK_EVENT) {
        GetSystemTime(&sysTime);
        SystemTimeToFileTime(&sysTime, &fileTime);
        thisTime.LowPart = fileTime.dwLowDateTime;
        thisTime.HighPart = fileTime.dwHighDateTime;
        if (lastTime.QuadPart + 10000000 < thisTime.QuadPart) {
            lastTime.QuadPart = thisTime.QuadPart;
            return TRUE;
        }
    }
    return FALSE;
}

enum {
    ArgCmd = 0,
    ArgAction,
    ArgSocket,
    ArgDir,
    ArgEnv,
    ArgCmdLine,
    ArgMsg,
    ArgCount
};

/* syntax: $0 {"run"|"debug"} <pid-socket> <workdir> <env-file> <cmdline> <continuation-msg> */
/* exit codes: 0 = ok, 1 = invocation error, 3 = internal error */
int main()
{
    int argc;
    int creationFlags;
    wchar_t **argv;
    wchar_t *env = 0;
    STARTUPINFOW si;
    PROCESS_INFORMATION pi;
    DEBUG_EVENT dbev;

    argv = CommandLineToArgvW(GetCommandLine(), &argc);

    if (argc != ArgCount) {
        fprintf(stderr, "This is an internal helper of Qt Creator. Do not run it manually.\n");
        return 1;
    }
    sleepMsg = argv[ArgMsg];

    /* Connect to the master, i.e. Creator. */
    if (!(qtcFd = _wfopen(argv[ArgSocket], L"w"))) {
        fprintf(stderr, "Cannot connect creator comm pipe %S: %s\n",
                argv[ArgSocket], strerror(errno));
        doExit(1);
    }

    if (*argv[ArgDir] && !SetCurrentDirectoryW(argv[ArgDir])) {
        /* Only expected error: no such file or direcotry */
        sendMsg("err:chdir %d\n", GetLastError());
        return 1;
    }

    if (*argv[ArgEnv]) {
        FILE *envFd;
        long size;
        if (!(envFd = _wfopen(argv[ArgEnv], L"r"))) {
            fprintf(stderr, "Cannot read creator env file %S: %s\n",
                    argv[ArgEnv], strerror(errno));
            doExit(1);
        }
        fseek(envFd, 0, SEEK_END);
        size = ftell(envFd);
        rewind(envFd);
        env = malloc(size);
        if (fread(env, 1, size, envFd) != size) {
            perror("Failed to read env file");
            doExit(1);
        }
        fclose(envFd);
    }

    ZeroMemory(&pi, sizeof(pi));
    ZeroMemory(&si, sizeof(si));
    si.cb = sizeof(si);

    creationFlags = CREATE_UNICODE_ENVIRONMENT;
    if (!wcscmp(argv[ArgAction], L"debug"))
        creationFlags |= DEBUG_ONLY_THIS_PROCESS;
    if (!CreateProcessW(0, argv[ArgCmdLine], 0, 0, FALSE, creationFlags, env, 0, &si, &pi)) {
        /* Only expected error: no such file or direcotry, i.e. executable not found */
        sendMsg("err:exec %d\n", GetLastError());
        doExit(1);
    }

    /* This is somewhat convoluted. What we actually want is creating a
       suspended process and letting gdb attach to it. Unfortunately,
       the Windows kernel runs amok when we attempt this.
       So instead we start a debugged process, eat all the initial
       debug events, suspend the process and detach from it. If gdb
       tries to attach *now*, everthing goes smoothly. Yay. */
    if (creationFlags & DEBUG_ONLY_THIS_PROCESS) {
        do {
            if (!WaitForDebugEvent (&dbev, INFINITE))
                systemError("Cannot fetch debug event, error %d\n");
            if (dbev.dwDebugEventCode == EXCEPTION_DEBUG_EVENT) {
                /* The first exception to be delivered is a trap
                   which indicates completion of startup. */
                if (SuspendThread(pi.hThread) == (DWORD)-1)
                    systemError("Cannot suspend debugee, error %d\n");
            }
            if (!ContinueDebugEvent(dbev.dwProcessId, dbev.dwThreadId, DBG_CONTINUE))
                systemError("Cannot continue debug event, error %d\n");
        } while (dbev.dwDebugEventCode != EXCEPTION_DEBUG_EVENT);
        if (!DebugActiveProcessStop(dbev.dwProcessId))
            systemError("Cannot detach from debugee, error %d\n");
    }

    SetConsoleCtrlHandler(ctrlHandler, TRUE);

    sendMsg("pid %d\n", pi.dwProcessId);

    if (WaitForSingleObject(pi.hProcess, INFINITE) == WAIT_FAILED)
        systemError("Wait for debugee failed, error %d\n");
    doExit(0);
    return 0;
}