crashdump.c

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/*-------------------------------------------------------------------------
 *
 * crashdump.c
 *         Automatic crash dump creation for PostgreSQL on Windows
 *
 * The crashdump feature traps unhandled win32 exceptions produced by the
 * backend, and tries to produce a Windows MiniDump crash
 * dump for later debugging and analysis. The machine performing the dump
 * doesn't need any special debugging tools; the user only needs to send
 * the dump to somebody who has the same version of PostgreSQL and has debugging
 * tools.
 *
 * crashdump module originally by Craig Ringer <ringerc@ringerc.id.au>
 *
 * LIMITATIONS
 * ===========
 * This *won't* work in hard OOM situations or stack overflows.
 *
 * For those, it'd be necessary to take a much more complicated approach where
 * the handler switches to a new stack (if it can) and forks a helper process
 * to debug it self.
 *
 * POSSIBLE FUTURE WORK
 * ====================
 * For bonus points, the crash dump format permits embedding of user-supplied
 * data. If there's anything else that should always be supplied with a crash
 * dump (postgresql.conf? Last few lines of a log file?), it could potentially
 * be added, though at the cost of a greater chance of the crash dump failing.
 *
 *
 * Portions Copyright (c) 1996-2026, PostgreSQL Global Development Group
 *
 * IDENTIFICATION
 *    src/backend/port/win32/crashdump.c
 *
 *-------------------------------------------------------------------------
 */
 
#include "postgres.h"
 
#include <dbghelp.h>
 
/*
 * Much of the following code is based on CodeProject and MSDN examples,
 * particularly
 * http://www.codeproject.com/KB/debug/postmortemdebug_standalone1.aspx
 *
 * Useful MSDN articles:
 *
 * http://msdn.microsoft.com/en-us/library/ff805116(v=VS.85).aspx
 * http://msdn.microsoft.com/en-us/library/ms679294(VS.85).aspx
 *
 * Other useful articles on working with minidumps:
 * http://www.debuginfo.com/articles/effminidumps.html
 */
 
typedef BOOL (WINAPI * MINIDUMPWRITEDUMP) (HANDLE hProcess, DWORD dwPid, HANDLE hFile, MINIDUMP_TYPE DumpType,
                                           CONST PMINIDUMP_EXCEPTION_INFORMATION ExceptionParam,
                                           CONST PMINIDUMP_USER_STREAM_INFORMATION UserStreamParam,
                                           CONST PMINIDUMP_CALLBACK_INFORMATION CallbackParam
);
 
 
/*
 * This function is the exception handler passed to SetUnhandledExceptionFilter.
 * It's invoked only if there's an unhandled exception. The handler will use
 * dbghelp.dll to generate a crash dump, then resume the normal unhandled
 * exception process, which will generally exit with an error message from
 * the runtime.
 *
 * This function is run under the unhandled exception handler, effectively
 * in a crash context, so it should be careful with memory and avoid using
 * any PostgreSQL functions.
 */
static LONG WINAPI
crashDumpHandler(struct _EXCEPTION_POINTERS *pExceptionInfo)
{
    /*
     * We only write crash dumps if the "crashdumps" directory within the
     * postgres data directory exists.
     */
    DWORD       attribs = GetFileAttributesA("crashdumps");
 
    if (attribs != INVALID_FILE_ATTRIBUTES && (attribs & FILE_ATTRIBUTE_DIRECTORY))
    {
        /* 'crashdumps' exists and is a directory. Try to write a dump' */
        HMODULE     hDll = NULL;
        MINIDUMPWRITEDUMP pDump = NULL;
        MINIDUMP_TYPE dumpType;
        char        dumpPath[_MAX_PATH];
        HANDLE      selfProcHandle = GetCurrentProcess();
        DWORD       selfPid = GetProcessId(selfProcHandle);
        HANDLE      dumpFile;
        DWORD       systemTicks;
        struct _MINIDUMP_EXCEPTION_INFORMATION ExInfo;
 
        ExInfo.ThreadId = GetCurrentThreadId();
        ExInfo.ExceptionPointers = pExceptionInfo;
        ExInfo.ClientPointers = FALSE;
 
        /* Load the dbghelp.dll library and functions */
        hDll = LoadLibrary("dbghelp.dll");
        if (hDll == NULL)
        {
            write_stderr("could not load dbghelp.dll, cannot write crash dump\n");
            return EXCEPTION_CONTINUE_SEARCH;
        }
 
        pDump = (MINIDUMPWRITEDUMP) (pg_funcptr_t) GetProcAddress(hDll, "MiniDumpWriteDump");
 
        if (pDump == NULL)
        {
            write_stderr("could not load required functions in dbghelp.dll, cannot write crash dump\n");
            return EXCEPTION_CONTINUE_SEARCH;
        }
 
        /*
         * Dump as much as we can, except shared memory, code segments, and
         * memory mapped files. Exactly what we can dump depends on the
         * version of dbghelp.dll, see:
         * http://msdn.microsoft.com/en-us/library/ms680519(v=VS.85).aspx
         */
        dumpType = MiniDumpNormal | MiniDumpWithHandleData |
            MiniDumpWithDataSegs;
 
        if (GetProcAddress(hDll, "EnumDirTree") != NULL)
        {
            /* If this function exists, we have version 5.2 or newer */
            dumpType |= MiniDumpWithIndirectlyReferencedMemory |
                MiniDumpWithPrivateReadWriteMemory;
        }
 
        systemTicks = GetTickCount();
        snprintf(dumpPath, _MAX_PATH,
                 "crashdumps\\postgres-pid%0i-%0i.mdmp",
                 (int) selfPid, (int) systemTicks);
        dumpPath[_MAX_PATH - 1] = '\0';
 
        dumpFile = CreateFile(dumpPath, GENERIC_WRITE, FILE_SHARE_WRITE,
                              NULL, CREATE_ALWAYS, FILE_ATTRIBUTE_NORMAL,
                              NULL);
        if (dumpFile == INVALID_HANDLE_VALUE)
        {
            write_stderr("could not open crash dump file \"%s\" for writing: error code %lu\n",
                         dumpPath, GetLastError());
            return EXCEPTION_CONTINUE_SEARCH;
        }
 
        if ((*pDump) (selfProcHandle, selfPid, dumpFile, dumpType, &ExInfo,
                      NULL, NULL))
            write_stderr("wrote crash dump to file \"%s\"\n", dumpPath);
        else
            write_stderr("could not write crash dump to file \"%s\": error code %lu\n",
                         dumpPath, GetLastError());
 
        CloseHandle(dumpFile);
    }
 
    return EXCEPTION_CONTINUE_SEARCH;
}
 
 
void
pgwin32_install_crashdump_handler(void)
{
    SetUnhandledExceptionFilter(crashDumpHandler);
}