[bpt/emacs.git] / nt / INSTALL

		    Building and Installing Emacs on Windows
                          (from 95 to 7 and beyond)

  Copyright (C) 2001-2012  Free Software Foundation, Inc.
  See the end of the file for license conditions.

* For the impatient

  Here are the concise instructions for configuring and building the
  native Windows binary of Emacs, for those who want to skip the
  complex explanations and ``just do it'':

  Do not use this recipe with Cygwin.  For building on Cygwin,
  use the normal installation instructions, ../INSTALL.

  If you have a Cygwin or MSYS port of Bash on your Path, you will be
  better off removing it from PATH.  (For details, search for "MSYS
  sh.exe" below.)

  1. Change to the `nt' directory (the directory of this file):

       cd nt

  2. Run configure.bat.

  2a.If you use MSVC, set up the build environment by running the
     SetEnv.cmd batch file from the appropriate SDK directory.  (Skip
     this step if you are using MinGW.)  For example:

       "C:\Program Files\Microsoft SDKs\Windows\v7.1\Bin\SetEnv.cmd" /x86 /Debug

      if you are going to compile a debug version, or

       "C:\Program Files\Microsoft SDKs\Windows\v7.1\Bin\SetEnv.cmd" /x86 /Release

      if you are going to compile an optimized version.

  2b.From the COMMAND.COM/CMD.EXE command prompt type:

       configure

     From a Unixy shell prompt:

       cmd /c configure.bat
     or
       command.com /c configure.bat

  3. Run the Make utility suitable for your environment.  If you build
     with the Microsoft's Visual C compiler:

       nmake

     For the development environments based on GNU GCC (MinGW, MSYS,
     Cygwin - but see notes about Cygwin make below), depending on how
     Make is called, it could be:

       make
     or
       mingw32-make
     or
       gnumake
     or
       gmake

     (If you are building from Bazaar, say "make bootstrap" or "nmake
     bootstrap" instead, and avoid using Cygwin make.)

     With GNU Make, you can use the -j command-line option to have
     Make execute several commands at once, like this:

       gmake -j 2

     (With versions of GNU Make before 3.82, you need also set the
     XMFLAGS variable, like this:

       gmake -j 2 XMFLAGS="-j 2"

     The XMFLAGS variable overrides the default behavior of version
     3.82 and older of GNU Make on Windows, whereby recursive Make
     invocations reset the maximum number of simultaneous commands to
     1.  The above command allows up to 4 simultaneous commands at
     once in the top-level Make, and up to 3 in each one of the
     recursive Make's.)

  4. Generate the Info manuals (only if you are building out of Bazaar,
     and if you have makeinfo.exe installed):

     make info

     (change "make" to "nmake" if you use MSVC).

  5. Install the produced binaries:

     make install

  That's it!

  If these short instructions somehow fail, read the rest of this
  file.

* Preliminaries

  If you want to build a Cygwin port of Emacs, use the instructions in
  the INSTALL file in the main Emacs directory (the parent of this
  directory).  These instructions are for building a native Windows
  binary of Emacs.

  If you used WinZip to unpack the distribution, we suggest to
  remove the files and unpack again with a different program!
  WinZip is known to create some subtle and hard to debug problems,
  such as converting files to DOS CR-LF format, not creating empty
  directories, etc.  We suggest to use djtarnt.exe from the GNU FTP
  site.

  In addition to this file, you should also read INSTALL.BZR in the
  parent directory, and make sure that you have a version of
  "touch.exe" in your path, and that it will create files that do not
  yet exist.

* Supported development environments

  To compile Emacs, you will need either Microsoft Visual C++ 2.0, or
  later and nmake, or a Windows port of GCC 2.95 or later with MinGW
  and W32 API support and a port of GNU Make.  You can use the Cygwin
  ports of GCC, but Emacs requires the MinGW headers and libraries to
  build (latest versions of the Cygwin toolkit, at least since v1.3.3,
  include the MinGW headers and libraries as an integral part).

  The rest of this file assumes you have a working development
  environment.  If you just installed such an environment, try
  building a trivial C "Hello world" program, and see if it works.  If
  it doesn't work, resolve that problem first!  If you use Microsoft
  Visual Studio .NET 2003, don't forget to run the VCVARS32.BAT batch
  file from the `Bin' subdirectory of the directory where you have
  installed VS.NET.  With other versions of MSVC, run the SetEnv.cmd
  batch file from the `Bin' subdirectory of the directory where you
  have the SDK installed.

  If you use the MinGW port of GCC and GNU Make to build Emacs, there
  are some compatibility issues wrt Make and the shell that is run by
  Make, either the standard COMMAND.COM/CMD.EXE supplied with Windows
  or sh.exe, a port of a Unixy shell.  For reference, below is a list
  of which builds of GNU Make are known to work or not, and whether
  they work in the presence and/or absence of sh.exe, the Cygwin port
  of Bash.  Note that any version of Make that is compiled with Cygwin
  will only work with Cygwin tools, due to the use of Cygwin style
  paths.  This means Cygwin Make is unsuitable for building parts of
  Emacs that need to invoke Emacs itself (leim and "make bootstrap",
  for example).  Also see the Trouble-shooting section below if you
  decide to go ahead and use Cygwin make.

  In addition, using 4NT or TCC as your shell is known to fail the
  build process, at least since 4NT version 3.01.  Use CMD.EXE, the
  default Windows shell, instead.  MSYS sh.exe also appears to cause
  various problems, e.g., it is known to cause failures in commands
  like "cmd /c FOO" in the Makefiles, because it thinks "/c" is a
  Unix-style file name that needs conversion to the Windows format.
  If you have MSYS installed, try "make SHELL=cmd.exe" to force the
  use of cmd.exe instead of the MSYS sh.exe.

                                         sh exists     no sh

    cygwin b20.1 make (3.75):            fails[1, 5]   fails[2, 5]
    MSVC compiled gmake 3.77:            okay          okay
    MSVC compiled gmake 3.78.1:          okay          okay
    MSVC compiled gmake 3.79.1:          okay          okay
    mingw32/gcc-2.92.2 make (3.77):      okay          okay[4]
    cygwin compiled gmake 3.77:          fails[1, 5]   fails[2, 5]
    cygwin compiled make 3.78.1:         fails[5]      fails[2, 5]
    cygwin compiled make 3.79.1:         fails[3, 5]   fails[2?, 5]
    cygwin compiled make 3.80:           okay[6]       fails?[7]
    cygwin compiled make 3.81:           fails         fails?[7]
    mingw32 compiled make 3.79.1:        okay          okay
    mingw32 compiled make 3.80:          okay          okay[7]
    mingw32 compiled make 3.81:          okay          okay[8]

  Notes:

    [1] doesn't cope with makefiles with DOS line endings, so must mount
        emacs source with text!=binary.
    [2] fails when needs to invoke shell commands; okay invoking gcc etc.
    [3] requires LC_MESSAGES support to build; cannot build with early
        versions of Cygwin.
    [4] may fail on Windows 9X and Windows ME; if so, install Bash.
    [5] fails when building leim due to the use of cygwin style paths.
        May work if building emacs without leim.
    [6] need to uncomment 3 lines in nt/gmake.defs that invoke `cygpath'
    	(look for "cygpath" near line 85 of gmake.defs).
    [7] not recommended; please report if you try this combination.
    [8] tested only on Windows XP.

  Other compilers may work, but specific reports from people that have
  tried suggest that the Intel C compiler (for example) may produce an
  Emacs executable with strange filename completion behavior.  Unless
  you would like to assist by finding and fixing the cause of any bugs
  like this, we recommend the use of the supported compilers mentioned
  in the previous paragraph.

  You will also need a copy of the POSIX cp, rm and mv programs.  These
  and other useful POSIX utilities can be obtained from one of several
  projects:

  * http://gnuwin32.sourceforge.net/              ( GnuWin32 )
  * http://www.mingw.org/                         ( MinGW    )
  * http://www.cygwin.com/                        ( Cygwin   )
  * http://unxutils.sourceforge.net/              ( UnxUtils )

  If you build Emacs on 16-bit versions of Windows (9X or ME), we
  suggest to install the Cygwin port of Bash.  That is because the
  native Windows shell COMMAND.COM is too limited; the Emacs build
  procedure tries very hard to support even such limited shells, but
  as none of the Windows developers of Emacs work on Windows 9X, we
  cannot guarantee that it works without a more powerful shell.

  Additional instructions and help for building Emacs on Windows can be
  found at the Emacs Wiki:

    http://www.emacswiki.org/cgi-bin/wiki/WThirtyTwoInstallationKit

  and on these URLs:

    http://ourcomments.org/Emacs/w32-build-emacs.html
    http://derekslager.com/blog/posts/2007/01/emacs-hack-3-compile-emacs-from-cvs-on-windows.ashx

  Both of those pages were written before Emacs switched from CVS to
  Bazaar, but the parts about building Emacs still apply in Bazaar.
  The second URL has instructions for building with MSVC, as well as
  with MinGW, while the first URL covers only MinGW, but has more
  details about it.

* Configuring

  Configuration of Emacs is now handled by running configure.bat in the
  `nt' subdirectory.  It will detect which compiler you have available,
  and generate makefiles accordingly.  You can override the compiler
  detection, and control optimization and debug settings, by specifying
  options on the command line when invoking configure.

  To configure Emacs to build with GCC or MSVC, whichever is available,
  simply change to the `nt' subdirectory and run `configure.bat' with no
  options.  To see what options are available, run `configure --help'.
  Do NOT use the --no-debug option to configure.bat unless you are
  absolutely sure the produced binaries will never need to be run under
  a debugger.

  Because of limitations of the stock Windows command shells, special
  care is needed to pass some characters in the arguments of the
  --cflags and --ldflags options.  Backslashes should not be used in
  file names passed to the compiler and linker via these options.  Use
  forward slashes instead.  If the arguments to these two options
  include the `=' character, like when passing a -DFOO=bar preprocessor
  option, the argument with the `=' character should be enclosed in
  quotes, like this:

    configure --cflags "-DFOO=bar"

  Support for options that include the `=' character require "command
  extensions" to be enabled.  (They are enabled by default, but your
  system administrator could have changed that.  See "cmd /?" for
  details.)  If command extensions are disabled, a warning message might
  be displayed informing you that "using parameters that include the =
  character by enclosing them in quotes will not be supported."

  You may also use the --cflags and --ldflags options to pass
  additional parameters to the compiler and linker, respectively; they
  are frequently used to pass -I and -L flags to specify supplementary
  include and library directories.  If a directory name includes
  spaces, you will need to enclose it in quotes, as follows
  -I"C:/Program Files/GnuTLS-2.10.1/include".  Note that only the
  directory name is enclosed in quotes, not the entire argument.  Also
  note that this functionality is only supported if command extensions
  are available.  If command extensions are disabled and you attempt to
  use this functionality you may see the following warning message
  "Error in --cflags argument: ... Backslashes and quotes cannot be
  used with --cflags.  Please use forward slashes for filenames and
  paths (e.g. when passing directories to -I)."

  N.B.  It is normal to see a few error messages output while configure
  is running, when gcc support is being tested.  These cannot be
  suppressed because of limitations in the Windows 9X command.com shell.

  You are encouraged to look at the file config.log which shows details
  for failed tests, after configure.bat finishes.  Any unexplained failure
  should be investigated and perhaps reported as a bug (see the section
  about reporting bugs in the file README in this directory and in the
  Emacs manual).

* Optional image library support

  In addition to its "native" image formats (pbm and xbm), Emacs can
  handle other image types: xpm, tiff, gif, png, jpeg and experimental
  support for svg.

  To build Emacs with support for them, the corresponding headers must
  be in the include path when the configure script is run.  This can
  be setup using environment variables, or by specifying --cflags
  -I... options on the command-line to configure.bat.  The configure
  script will report whether it was able to detect the headers.  If
  the results of this testing appear to be incorrect, please look for
  details in the file config.log: it will show the failed test
  programs and compiler error messages that should explain what is
  wrong.  (Usually, any such failures happen because some headers are
  missing due to bad packaging of the image support libraries.)

  Note that any file path passed to the compiler or linker must use
  forward slashes; using backslashes will cause compiler warnings or
  errors about unrecognized escape sequences.

  To use the external image support, the DLLs implementing the
  functionality must be found when Emacs first needs them, either on the
  PATH, or in the same directory as emacs.exe.  Failure to find a
  library is not an error; the associated image format will simply be
  unavailable.  Note that once Emacs has determined that a library can
  not be found, there's no way to force it to try again, other than
  restarting.  See the variable `dynamic-library-alist' to configure the
  expected names of the libraries.

  Some image libraries have dependencies on one another, or on zlib.
  For example, tiff support depends on the jpeg library.  If you did not
  compile the libraries yourself, you must make sure that any dependency
  is in the PATH or otherwise accessible and that the binaries are
  compatible (for example, that they were built with the same compiler).

  Binaries for the image libraries (among many others) can be found at
  the GnuWin32 project.  PNG, JPEG and TIFF libraries are also
  included with GTK, which is installed along with other Free Software
  that requires it.  These are built with MinGW, but they can be used
  with both GCC/MinGW and MSVC builds of Emacs.  See the info on
  http://ourcomments.org/Emacs/w32-build-emacs.html, under "How to Get
  Images Support", for more details about installing image support
  libraries.  Note specifically that, due to some packaging snafus in
  the GnuWin32-supplied image libraries, you will need to download
  _source_ packages for some of the libraries in order to get the
  header files necessary for building Emacs with image support.

  If GTK 2.0 is installed, addpm will arrange for its image libraries
  to be on the DLL search path for Emacs.

  For PNG images, we recommend to use versions 1.4.x and later of
  libpng, because previous versions had security issues.  You can find
  precompiled libraries and headers on the GTK download page for
  Windows (http://www.gtk.org/download/win32.php).

  Versions 1.4.0 and later of libpng are binary incompatible with
  earlier versions, so Emacs will only look for libpng libraries which
  are compatible with the version it was compiled against.  That
  version is given by the value of the Lisp variable `libpng-version';
  e.g., 10403 means version 1.4.3.  The variable `dynamic-library-alist'
  is automatically set to name only those DLL names that are known to
  be compatible with the version given by `libpng-version'.  If PNG
  support does not work for you even though you have the support DLL
  installed, check the name of the installed DLL against
  `dynamic-library-alist' and the value of `libpng-version', and
  download compatible DLLs if needed.

* Optional GnuTLS support

  If configure.bat finds the gnutls/gnutls.h file in the include path,
  Emacs is built with GnuTLS support by default; to avoid that you can
  pass the argument --without-gnutls.

  In order to support GnuTLS at runtime, a GnuTLS-enabled Emacs must
  be able to find the relevant DLLs during startup; failure to do so
  is not an error, but GnuTLS won't be available to the running
  session.

  You can get pre-built binaries (including any required DLL and the
  header files) at http://sourceforge.net/projects/ezwinports/files/.

* Optional libxml2 support

  If configure.bat finds the libxml/HTMLparser.h file in the include path,
  Emacs is built with libxml2 support by default; to avoid that you can
  pass the argument --without-libxml2.

  In order to support libxml2 at runtime, a libxml2-enabled Emacs must
  be able to find the relevant DLLs during startup; failure to do so
  is not an error, but libxml2 features won't be available to the
  running session.

  One place where you can get pre-built Windows binaries of libxml2
  (including any required DLL and the header files) is here:

     http://sourceforge.net/projects/ezwinports/files/

  To compile Emacs with libxml2 from that site, you will need to pass
  the "--cflags -I/path/to/include/libxml2" option to configure.bat,
  because libxml2 header files are installed in the include/libxml2
  subdirectory of the directory where you unzip the binary
  distribution.  Other binary distributions might use other
  directories, although include/libxml2 is the canonical place where
  libxml2 headers are installed on Posix platforms.

  You will also need to install the libiconv "development" tarball,
  because the libiconv headers need to be available to the compiler
  when you compile with libxml2 support.  A MinGW port of libiconv can
  be found on the MinGW site:

   http://sourceforge.net/projects/mingw/files/MinGW/Base/libiconv/

  You need the libiconv-X.Y.Z-N-mingw32-dev.tar.lzma tarball from that
  site.

* Experimental SVG support

  SVG support is currently experimental, and not built by default.
  Specify --with-svg and ensure you have all the dependencies in your
  include path.  Unless you have built a minimalist librsvg yourself
  (untested), librsvg depends on a significant chunk of GTK+ to build,
  plus a few Gnome libraries, libxml2, libbz2 and zlib at runtime.  The
  easiest way to obtain the dependencies required for building is to
  download a pre-bundled GTK+ development environment for Windows.
  GTK puts its header files all over the place, so you will need to
  run pkgconfig to list the include path you will need (either passed
  to configure.bat as --cflags options, or set in the environment).

  To use librsvg at runtime, ensure that librsvg and its dependencies
  are on your PATH.  If you didn't build librsvg yourself, you will
  need to check with where you downloaded it from for the
  dependencies, as there are different build options.  If it is a
  short list, then it most likely only lists the immediate
  dependencies of librsvg, but the dependencies themselves have
  dependencies - so don't download individual libraries from GTK+,
  download and install the whole thing.  If you think you've got all
  the dependencies and SVG support is still not working, check your
  PATH for other libraries that shadow the ones you downloaded.
  Libraries of the same name from different sources may not be
  compatible, this problem was encountered with libbzip2 from GnuWin32
  with libcroco from gnome.org.

  If you can see etc/images/splash.svg, then you have managed to get
  SVG support working.  Congratulations for making it through DLL hell
  to this point.  You'll probably find that some SVG images crash
  Emacs.  Problems have been observed in some images that contain
  text, they seem to be a problem in the Windows port of Pango, or
  maybe a problem with the way Cairo or librsvg is using it that
  doesn't show up on other platforms.

* Optional extra runtime checks

  The configure.bat option --enable-checking builds Emacs with some
  optional extra runtime checks and assertions enabled.  This may be
  useful for debugging.

* Optional extra libraries

  You can pass --lib LIBNAME option to configure.bat to cause Emacs to
  link with the specified library.  You can use this option more than once.

* Building

  After running configure, simply run the appropriate `make' program for
  your compiler to build Emacs.  For MSVC, this is nmake; for GCC, it is
  GNU make.  (If you are building out of Bazaar, say "make bootstrap" or
  "nmake bootstrap" instead.)

  As the files are compiled, you will see some warning messages
  declaring that some functions don't return a value, or that some data
  conversions will be lossy, etc.  You can safely ignore these messages.
  The warnings may be fixed in the main FSF source at some point, but
  until then we will just live with them.

  With GNU Make, you can use the -j command-line option to have Make
  execute several commands at once, like this:

    gmake -j 4 XMFLAGS="-j 3"

  The XMFLAGS variable overrides the default behavior of GNU Make on
  Windows, whereby recursive Make invocations reset the maximum number
  of simultaneous commands to 1.  The above command allows up to 4
  simultaneous commands at once in the top-level Make, and up to 3 in
  each one of the recursive Make's; you can use other numbers of jobs,
  if you wish.

  If you are building from Bazaar, the following commands will produce
  the Info manuals (which are not part of the Bazaar sources):

    make info
  or
    nmake info

  Note that you will need makeinfo.exe (from the GNU Texinfo package)
  in order for this command to succeed.

* Installing

  To install Emacs after it has compiled, simply run `nmake install'
  or `make install', depending on which version of the Make utility
  do you have.

  By default, Emacs will be installed in the location where it was
  built, but a different location can be specified either using the
  --prefix option to configure, or by setting INSTALL_DIR when running
  make, like so:

     make install INSTALL_DIR=D:/emacs

  (for `nmake', type "nmake install INSTALL_DIR=D:/emacs" instead).

  The install process will run addpm to setup the registry entries, and
  to create a Start menu icon for Emacs.

* Make targets

  The following make targets may be used by users building the source
  distribution, or users who have checked out of Bazaar after
  an initial bootstrapping.

  make
  Builds Emacs from the available sources and pre-compiled lisp files.

  make install
  Installs programs to the bin directory, and runs addpm to create
  Start Menu icons.

  make clean
  Removes object and executable files produced by the build process in
  the current configuration.  After make clean, you can rebuild with
  the same configuration using make.

  make distclean
  In addition to the files removed by make clean, this also removes
  Makefiles and other generated files to get back to the state of a
  freshly unpacked source distribution.  Note that this will not remove
  installed files, or the results of builds performed with different
  compiler or optimization options than the current configuration.
  After make distclean, it is necessary to run configure.bat followed
  by make to rebuild.

  make cleanall
  Removes object and executable files that may have been created by
  previous builds with different configure options, in addition to
  the files produced by the current configuration.

  make realclean
  Removes the installed files in the bin subdirectory in addition to
  the files removed by make cleanall.

  make dist
  Builds Emacs from the available sources and pre-compiled lisp files.
  Packages Emacs binaries as full distribution and barebin distribution.

  The following targets are intended only for use with the Bazaar sources.

  make bootstrap
  Creates a temporary emacs binary with lisp source files and
  uses it to compile the lisp files.  Once the lisp files are built,
  emacs is redumped with the compiled lisp.

  make recompile
  Recompiles any changed lisp files after an update.  This saves
  doing a full bootstrap after every update.  If this or a subsequent
  make fail, you probably need to perform a full bootstrap, though
  running this target multiple times may eventually sort out the
  interdependencies.

  make maintainer-clean
  Removes everything that can be recreated, including compiled lisp
  files, to get back to the state of a fresh Bazaar tree.  After make
  maintainer-clean, it is necessary to run configure.bat and make
  bootstrap to rebuild.  Occasionally it may be necessary to run this
  target after an update.

* Creating binary distributions

  Binary distributions (full and barebin distributions) can be
  automatically built and packaged from source tarballs or a bzr
  checkout.

  When building Emacs binary distributions, the --distfiles argument
  to configure.bat specifies files to be included in the bin directory
  of the binary distributions. This is intended for libraries that are
  not built as part of Emacs, e.g. image libraries.

  For example, specifying

	--distfiles D:\distfiles\libXpm.dll

  results in libXpm.dll being copied from D:\distfiles to the
  bin directory before packaging starts.

  Multiple files can be specified using multiple --distfiles arguments:

	--distfiles D:\distfiles\libXpm.dll --distfiles C:\jpeglib\jpeg.dll

  For packaging the binary distributions, the 'dist' make target uses
  7-Zip (http://www.7-zip.org), which must be installed and available
  on the Windows Path.


* Trouble-shooting

  The main problems that are likely to be encountered when building
  Emacs stem from using an old version of GCC, or old MinGW or W32 API
  headers.  Additionally, Cygwin ports of GNU make may require the Emacs
  source tree to be mounted with text!=binary, because the makefiles
  generated by configure.bat necessarily use DOS line endings.  Also,
  Cygwin ports of make must run in UNIX mode, either by specifying
  --unix on the command line, or MAKE_MODE=UNIX in the environment.

  When configure runs, it attempts to detect when GCC itself, or the
  headers it is using, are not suitable for building Emacs.  GCC version
  2.95 or later is needed, because that is when the Windows port gained
  sufficient support for anonymous structs and unions to cope with some
  definitions from winnt.h that are used by addsection.c.
  Older versions of the W32 API headers that come with Cygwin and MinGW
  may be missing some definitions required by Emacs, or broken in other
  ways.  In particular, uniscribe APIs were added to MinGW CVS only on
  2006-03-26, so releases from before then cannot be used.

  When in doubt about correctness of what configure did, look at the file
  config.log, which shows all the failed test programs and compiler
  messages associated with the failures.  If that doesn't give a clue,
  please report the problems, together with the relevant fragments from
  config.log, as bugs.

  If configure succeeds, but make fails, install the Cygwin port of
  Bash, even if the table above indicates that Emacs should be able to
  build without sh.exe.  (Some versions of Windows shells are too dumb
  for Makefile's used by Emacs.)

  If you are using certain Cygwin builds of GCC, such as Cygwin version
  1.1.8, you may need to specify some extra compiler flags like so:

    configure --with-gcc --cflags -mwin32 --cflags -D__MSVCRT__
      --ldflags -mwin32

  However, the latest Cygwin versions, such as 1.3.3, don't need those
  switches; you can simply use "configure --with-gcc".

  We will attempt to auto-detect the need for these flags in a future
  release.

* Debugging

  You should be able to debug Emacs using the debugger that is
  appropriate for the compiler you used, namely DevStudio or Windbg if
  compiled with MSVC, or GDB if compiled with GCC.  (GDB for Windows
  is available from the MinGW site, http://www.mingw.org/download.shtml.)

  When Emacs aborts due to a fatal internal error, Emacs on Windows
  pops up an Emacs Abort Dialog asking you whether you want to debug
  Emacs or terminate it.  If Emacs was built with MSVC, click YES
  twice, and Windbg or the DevStudio debugger will start up
  automatically.  If Emacs was built with GCC, first start GDB and
  attach it to the Emacs process with the "gdb -p EMACS-PID" command,
  where EMACS-PID is the Emacs process ID (which you can see in the
  Windows Task Manager), type the "continue" command inside GDB, and
  only then click YES on the abort dialog.  This will pass control to
  the debugger, and you will be able to debug the cause of the fatal
  error.

  The single most important thing to find out when Emacs aborts or
  crashes is where did that happen in the Emacs code.  This is called
  "backtrace".

  Emacs on Windows uses more than one thread.  When Emacs aborts due
  to a fatal error, the current thread may not be the application
  thread running Emacs code.  Therefore, to produce a meaningful
  backtrace from a debugger, you need to instruct it to show the
  backtrace for every thread.  With GDB, you do it like this:

   (gdb) thread apply all backtrace

  To run Emacs under a debugger to begin with, simply start it from
  the debugger.  With GDB, chdir to the `src' directory (if you have
  the source tree) or to a directory with the `.gdbinit' file (if you
  don't have the source tree), and type these commands:

    C:\whatever\src> gdb x:\path\to\emacs.exe
    (gdb) run <ARGUMENTS TO EMACS>

  Thereafter, use Emacs as usual; you can minimize the debugger
  window, if you like.  The debugger will take control if and when
  Emacs crashes.

  Emacs functions implemented in C use a naming convention that reflects
  their names in lisp.  The names of the C routines are the lisp names
  prefixed with 'F', and with dashes converted to underscores.  For
  example, the function call-process is implemented in C by
  Fcall_process.  Similarly, lisp variables are prefixed with 'V', again
  with dashes converted to underscores.  These conventions enable you to
  easily set breakpoints or examine familiar lisp variables by name.

  Since Emacs data is often in the form of a lisp object, and the
  Lisp_Object type is difficult to examine manually in a debugger,
  Emacs provides a helper routine called debug_print that prints out a
  readable representation of a Lisp_Object.  If you are using GDB,
  there is a .gdbinit file in the src directory which provides
  definitions that are useful for examining lisp objects.  Therefore,
  the following tips are mainly of interest when using MSVC.

  The output from debug_print is sent to stderr, and to the debugger
  via the OutputDebugString routine.  The output sent to stderr should
  be displayed in the console window that was opened when the
  emacs.exe executable was started.  The output sent to the debugger
  should be displayed in its "Debug" output window.

  When you are in the process of debugging Emacs and you would like to
  examine the contents of a Lisp_Object variable, pop up the QuickWatch
  window (QuickWatch has an eyeglass symbol on its button in the
  toolbar).  In the text field at the top of the window, enter
  debug_print(<variable>) and hit return.  For example, start and run
  Emacs in the debugger until it is waiting for user input.  Then click
  on the Break button in the debugger to halt execution.  Emacs should
  halt in ZwUserGetMessage waiting for an input event.  Use the Call
  Stack window to select the procedure w32_msp_pump up the call stack
  (see below for why you have to do this).  Open the QuickWatch window
  and enter debug_print(Vexec_path).  Evaluating this expression will
  then print out the contents of the lisp variable exec-path.

  If QuickWatch reports that the symbol is unknown, then check the call
  stack in the Call Stack window.  If the selected frame in the call
  stack is not an Emacs procedure, then the debugger won't recognize
  Emacs symbols.  Instead, select a frame that is inside an Emacs
  procedure and try using debug_print again.

  If QuickWatch invokes debug_print but nothing happens, then check the
  thread that is selected in the debugger.  If the selected thread is
  not the last thread to run (the "current" thread), then it cannot be
  used to execute debug_print.  Use the Debug menu to select the current
  thread and try using debug_print again.  Note that the debugger halts
  execution (e.g., due to a breakpoint) in the context of the current
  thread, so this should only be a problem if you've explicitly switched
  threads.

\f
This file is part of GNU Emacs.

GNU Emacs is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.

GNU Emacs is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.