/*-------------------------------------------------------------------------
 *
 * win32_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) 1996-2017, PostgreSQL Global Development Group
 *
 * IDENTIFICATION
 *	  src/backend/port/win32/crashdump.c
 *
 *-------------------------------------------------------------------------
 */

#include "postgres.h"

#define WIN32_LEAN_AND_MEAN

/*
 * Some versions of the MS SDK contain "typedef enum { ... } ;" which the MS
 * compiler quite sanely complains about. Well done, Microsoft.
 * This pragma disables the warning just while we include the header.
 * The pragma is known to work with all (as at the time of writing) supported
 * versions of MSVC.
 */
#ifdef _MSC_VER
#pragma warning(push)
#pragma warning(disable : 4091)
#endif
#include <dbghelp.h>
#ifdef _MSC_VER
#pragma warning(pop)
#endif

/*
 * 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) 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);
}
