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Christopher Faylor 1fd5e000ac import winsup-2000-02-17 snapshot
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@chapter Question and Answers
@section Where can I get more information?
@subsection Where's the documentation?
There are links to quite a lot of it on the main Cygwin project WWW page:
@file{http://sourceware.cygnus.com/cygwin/}
Be sure to at least read the Release Notes on the main WWW page, if
there are any.
Tool-specific documentation is available at:
@file{http://www.cygnus.com/pubs/gnupro/}
@subsection What Cygwin mailing lists can I join?
To subscribe to the main list, send a message to
cygwin-subscribe@@sourceware.cygnus.com. To unsubscribe from the
main list, send a message to cygwin-unsubscribe@@sourceware.cygnus.com.
In both cases, the subject and body of the message is ignored.
Similarly, to subscribe to the Cygwin annoucements list, send a message
to cygwin-announce-subscribe@@sourceware.cygnus.com. To unsubscribe,
send a message to cygwin-announce-unsubscribe@@sourceware.cygnus.com.
If you are going to help develop the Cygwin library by volunteering for
the project, you will want to subscribe to the Cygwin developers list,
called cygwin-developers. The same mechanism as described for the first
two lists works for this one as well.
There's an archive of the main mailing list at
@file{http://sourceware.cygnus.com/ml/cygwin/}
@subsection Why won't you/the mailing list answer my questions?
Perhaps your question has an answer that's already in the FAQ.
Perhaps nobody has time to answer your question. Perhaps nobody
knows the answer...
@section Installation and Setup
@subsection Why is the install of the tools failing?
If you are getting an error message saying "The decompression of
%s failed. There may not be enough free disk space in the TEMP
directory.", read on.
InstallShield has a bug where it fails with this message if there
are more than a certain number of files in your TEMP directory.
You can also get this message if you have files in your TEMP dir
named the same thing InstallShield wishes to name its files (probably
from past runs of other InstallShield install scripts) which it cannot,
for some reason, write over. Perhaps this will be fixed in a future
release of InstallShield.
Until then, clearing out your TEMP directory entirely should do it.
That will get rid of any files with conflicting names and solve the
"too many files" problem as well.
@subsection Help! I haven't created /tmp and tools are behaving strangely!
Many Unix tools (bash, byacc, etc.) expect that /tmp always exists.
This is not guaranteed in Win32 land. You should create /tmp or "mount"
the directory of your choice to /tmp to avoid this problem.
@subsection Why does bash spew out "49054596: No such file or directory"?
Are you sure you created a /tmp? The bash shell will print a
warning if it doesn't find a /tmp directory.
@subsection How do I set /etc up?
If you want a valid /etc set up (so "ls -l" will display correct
user information for example) and if you are running NT (preferably
with an NTFS file system), you should just need to create the /etc
directory on the filesystem mounted as / and then use mkpasswd and
mkgroup to create /etc/passwd and /etc/group respectively. Since
Windows 95/98's Win32 API is less complete, you're out of luck if
you're running Windows 95/98.
@subsection Bash says that it can't vfork (or just hangs). Why?
Most often this is because it can't find itself in the path. Make sure
that your path includes the directory where bash lives, before you start
it.
Also make sure you have a valid @code{/bin/sh.exe}. If you get errors
like 'no such file or directory' when you're trying to run a shell
script, which you know is there, then your problem is probably that bash
can't find @code{/bin/sh}.
@subsection How can I get bash to read my .bashrc file on startup?
Your .bashrc is read from your home directory specified by the HOME
environment variable. It uses /.bashrc if HOME is not set. So you need
to set HOME correctly, or move your .bashrc to the top of the drive
mounted as / in Cygwin.
@subsection How can I get bash filename completion to be case insensitive?
"shopt -s nocaseglob" should do the trick.
@subsection Can I use paths/filenames containing spaces in them?
Cygwin does support spaces in filenames and paths. That said, some
utilities that use the library may not, since files don't typically
contain spaces in Unix. If you stumble into problems with this, you
will need to either fix the utilities or stop using spaces in filenames
used by Cygwin tools.
@subsection Why can't I cd into a shortcut to a directory?
Cygwin does not follow MS Windows Explorer Shortcuts (*.lnk
files) yet. It sees a shortcut as a regular file and this you
cannot "cd" into it.
Some people have suggested replacing the current symbolic link scheme
with shortcuts. The major problem with this is that .LNK files would
then be used to symlink Cygwin paths that may or may not be valid
under native Win32 non-Cygwin applications such as Explorer.
@subsection I'm having basic problems with find. Why?
Make sure you are using the find that came with the Cygwin tools
and that you aren't picking up the Win32 find command instead. You
can verify that you are getting the right one by doing a "type find"
in bash.
@subsection Why don't cursor keys work under Win95/Win98?
Careful examination shows that they not just non-functional, but
rather behave strangely, for example, with NumLock off, keys on numeric
keyboard work, until you press usual cursor keys, when even numeric
stop working, but they start working again after hitting alphanumeric
key, etc. This reported to happen on localized versions of Win98 and
Win95, and not specific to Cygwin (there're known cases of Alt+Enter
(fullscreen/windowed toggle) not working and shifts sticking with
other programs). The cause of this problem is Microsoft keyboard
localizer which by default installed in 'autoexec.bat'. Corresponding
line looks like:
@example
keyb ru,,C:\WINDOWS\COMMAND\keybrd3.sys
@end example
(That's for russian locale.) You should comment that line if you want
your keys working properly. Of course, this will deprive you of your
local alphabet keyboard support, so you should think about
another localizer. exUSSR users are of course knowledgable of Keyrus
localizer, and it might work for other locales too, since it has keyboard
layout editor. But it has russian messages and documentation ;-(
Reference URL is http://www.hnet.ru/software/contrib/Utils/KeyRus/
(note the you may need to turn off Windows logo for Keyrus to operate
properly).
@subsection Is it OK to have multiple copies of the DLL?
It's a bad idea to have multiple versions of the cygwin DLL in
your path. They often conflict in funny ways. If you have
multiple versions, it's usually OK to get rid of (or rename)
all the older versions, keeping only the newest one.
It should be OK to have multiple copies of the *same* DLL
in your path, though.
@section Using Cygwin Releases
@subsection Why aren't man, groff, etc. included in the betas?
For obvious reasons, it isn't feasible for us to maintain and provide
binary distributions of every tool ported to work with the Cygwin
tools. However, it's likely that a man command will show up in a
distribution soon.
Many other tools have been ported and are referenced on the Cygwin web
site. man, groff, info, and many many other packages are all
available for download there.
@subsection Where can I find "less"?
The less pager binary is available for the first time in the 20.1
release. You will get it if you upgrade. It is also available from
various ftp locations on the Net. Search the mailing list archives for
the details.
@subsection Where can I find "more"?
If you are looking for the "more" pager, you should use the "less" pager
instead. See the last question and answer for more information.
@subsection Where can I find "which"?
While we don't include a which command, you can use the bash built
in "type" command which does something fairly similar.
@subsection How can I access other drives?
The best way is to use the "mount" command to mount the drive letter so
that you can refer to it with only single slashes:
@example
bash$ mkdir /c
bash$ mount c:/ /c
bash$ ls /c
....
@end example
This is done with textual substitution whenever a file is opened.
So if you're going to do @code{ls /c/bar} on a mount like the above
the guts will turn that into @code{ls c:/bar}.
Note that you only need to mount drives once. The mapping is kept
in the registry so mounts stay valid pretty much indefinitely.
You can only get rid of them with umount (or the registry editor).
The '-b' option to mount mounts the mountpoint in binary mode where text
and binary files are treated equivalently. This should only be
necessary for badly ported Unix programs where binary flags are missing
from open calls.
Since the beta 16 release, we also support a special means of accessing
other drive letters without using the @code{mount} command. This
support may disappear in a future Cygwin release because of the
collision between this scheme and UNC pathname support (one character
machine names don't work currently).
To do an "ls" on drive letter f:, do the following:
@example
bash$ ls //f/
@end example
Note that you can also access UNC paths in the standard way. Because of
the drive letter shortcut mentioned above, machine names in UNC paths
must be more than one character long.
@subsection How can I copy and paste into Cygwin console windows?
Under Windows NT, open the properties dialog of the console window.
The options contain a toggle button, named "Quick edit mode". It must
be ON. Save the properties.
Under Windows 9x, open the properties dialog of the console window.
Select the Misc tab. Uncheck Fast Pasting. Check QuickEdit.
@subsection What does "mount failed: Device or resource busy" mean?
This usually means that you are trying to mount to a location
already in use by mount. For example, if c: is mounted as '/'
and you try to mount d: there as well, you will get this error
message. First "umount" the old location, then "mount" the new one and
you should have better luck.
If you are trying to umount '/' and are getting this message, you may
need to run @code{regedit.exe} and change the "native" key for the '/'
mount in one of the mount points kept under
HKEY_CURRENT_USER/Software/Cygnus Solutions/CYGWIN.DLL setup/<version>
where <version> is the latest registry version associated with the
Cygwin library.
@subsection How can I share files between Unix and Windows?
During development, we have both Unix boxes running Samba and
NT/Windows 95/98 machines. We often build with cross-compilers
under Unix and copy binaries and source to the Windows system
or just toy with them directly off the Samba-mounted partition.
On dual-boot NT/Windows 9x machines, we usually use the FAT
filesystem so we can also access the files under Windows 9x.
@subsection Are mixed-case filenames possible with Cygwin?
Several Unix programs expect to be able to use to filenames
spelled the same way, but with different case. A prime example
of this is perl's configuration script, which wants @code{Makefile} and
@code{makefile}. WIN32 can't tell the difference between files with
just different case, so the configuration fails.
In releases prior to beta 16, mount had a special mixed case option
which renamed files in such a way as to allow mixed case filenames.
We chose to remove the support when we rewrote the path handling
code for beta 16.
@subsection What about DOS special filenames?
Files cannot be named com1, lpt1, or aux (to name a few); either as
the root filename or as the extension part. If you do, you'll have
trouble. Unix programs don't avoid these names which can make things
interesting. E.g., the perl distribution has a file called
@code{aux.sh}. The perl configuration tries to make sure that
@code{aux.sh} is there, but an operation on a file with the magic
letters 'aux' in it will hang.
@subsection When it hangs, how do I get it back?
If something goes wrong and the tools hang on you for some reason (easy
to do if you try and read a file called aux.sh), first try hitting ^C to
return to bash or the cmd prompt.
If you start up another shell, and applications don't run, it's a good
bet that the hung process is still running somewhere. Use the Task
Manager, pview, or a similar utility to kill the process.
And, if all else fails, there's always the reset button/power switch.
This should never be necessary under Windows NT.
@subsection Why the weird directory structure?
Why are cpp.exe, cc1.exe, etc., not in the bin directory?
Why more than one lib and include directory?
@smallexample
H-i586-cygwin32\lib\gcc-lib\...\egcs-2.91.57\include
x86-cygwin32\include
x86-cygwin32\H-i586-cygwin32\i586-cygwin32\include
@end smallexample
This way multiple releases for different hosts and targets can all
coexist in the same tree. H-i586-cygwin32 means hosted on
i586-cygwin32, common files shared by all hosts are in the top level
directories, target-specific files are in the
H-i586-cygwin32/i586-cygwin32
directory, etc...
If you had a server sharing files to a ppc NT machine and an x86 NT
machine, you could have both an H-i586-cygwin32 and an
H-powerpcle-cygwin32 directory without having to duplicate the top level
files that are the same for both hosts. If you built and installed an
i586-cygwin32 x mips-elf cross-compiler, you would have an
H-i586-cygwin32/mips-elf with its target-specific files and some
mips-elf- prefixed binaries in H-i586-cygwin32/bin.
Normally we also have another higher level directory that identifies the
release. Then multiple Cygwin releases can coexist with different
dll versions, giving:
@smallexample
cygnus/b19/H-i586-cygwin32
cygnus/cygwin-b20/H-i586-cygwin32
...
@end smallexample
In any case, this does add complexity to the directory structure but
it's worth it for people with more complex installations.
@subsection How do anti-virus programs like Cygwin?
One person reported that McAfee VirusScan for NT (and others?) is
incompatible with Cygwin. This is because it tries to scan the
newly loaded shared memory in the cygwin.dll, which can cause fork()s
to fail, wreaking havoc on many of the tools.
@subsection Why can't I run bash as a shell under NT Emacs?
Place the following code in your startup file and try again:
@smallexample
(load "comint")
(fset 'original-comint-exec-1 (symbol-function 'comint-exec-1))
(defun comint-exec-1 (name buffer command switches)
(let ((binary-process-input t)
(binary-process-output nil))
(original-comint-exec-1 name buffer command switches)))
@end smallexample
@subsection Where did the man/info pages go?
In order to save space and download times, we have stopped providing
the man/info files for the tools with the binary install since we are
not yet providing a man page or info reader. Both types of
documentation are available in a tar file available from the project ftp
site. Or consult the online documentation over the WWW.
@subsection Why can't B20's "cygcheck -s" find cpp?
This is a confusingly worded warning that will be reworded in future
versions. In fact, cygcheck should normally *not* find cpp; if it does,
it may be a problem (e.g. it might pick up Borland's cpp, which would
cause problems).
@subsection Why do I get a message saying Out of Queue slots?
"Out of queue slots!" generally occurs when you're trying to remove
many files that you do not have permission to remove (either because
you don't have permission, they are opened exclusively, etc). What
happens is Cygwin queues up these files with the supposition that it
will be possible to delete these files in the future. Assuming that
the permission of an affected file does change later on, the file will
be deleted as requested. However, if too many requests come in to
delete inaccessible files, the queue overflows and you get the message
you're asking about. Usually you can remedy this with a quick chmod,
close of a file, or other such thing. (Thanks to Larry Hall for
this explanation).
@subsection Why don't symlinks work on samba-mounted filesystems?
Symlinks are marked with "system" file attribute. Samba does not
enable this attribute by default. To enable it, consult your Samba
documentation and then add these lines to your samba configuration
file:
@smallexample
mask system = yes
create mask = 0775
@end smallexample
Note that the 0775 can be anything as long as the 0010 bit is set.
@subsection Why does df report sizes incorrectly.
There is a bug in the Win32 API function GetFreeDiskSpace that
makes it return incorrect values for disks larger than 2 GB in size.
Perhaps that may be your problem?
@subsection Has the screen program been ported yet?
Screen requires either unix domain sockets or fifoes. Neither of
them have been implemented in Cygwin yet.
@section Cygwin API Questions
@subsection How does everything work?
There's a C library which provides a Unix-style API. The
applications are linked with it and voila - they run on Windows.
The aim is to add all the goop necessary to make your apps run on
Windows into the C library. Then your apps should run on Unix and
Windows with no changes at the source level.
The C library is in a DLL, which makes basic applications quite small.
And it allows relatively easy upgrades to the Win32/Unix translation
layer, providing that dll changes stay backward-compatible.
For a good overview of Cygwin, you may want to read the paper on Cygwin
published by the Usenix Association in conjunction with the 2d Usenix NT
Symposium in August 1998. It is available in html format on the project
WWW site.
@subsection Are development snapshots for the Cygwin library available?
Yes. They're made whenever anything interesting happens inside the
Cygwin library (usually roughly on a nightly basis, depending on how much
is going on). They are only intended for those people who wish to
contribute code to the project. If you aren't going to be happy
debugging problems in a buggy snapshot, avoid these and wait for a real
release. The snapshots are available from
http://sourceware.cygnus.com/cygwin/snapshots/
@subsection How is the DOS/Unix CR/LF thing handled?
Let's start with some background.
In UNIX, a file is a file and what the file contains is whatever the
program/programmer/user told it to put into it. In Windows, a file is
also a file and what the file contains depends not only on the
program/programmer/user but also the file processing mode.
When processing in text mode, certain values of data are treated
specially. A \n (new line) written to the file will prepend a \r
(carriage return) so that if you `printf("Hello\n") you in fact get
"Hello\r\n". Upon reading this combination, the \r is removed and the
number of bytes returned by the read is 1 less than was actually read.
This tends to confuse programs dependant on ftell() and fseek(). A
Ctrl-Z encountered while reading a file sets the End Of File flags even
though it truly isn't the end of file.
One of Cygwin's goals is to make it possible to easily mix Cygwin-ported
Unix programs with generic Windows programs. As a result, Cygwin opens
files in text mode as is normal under Windows. In the accompanying
tools, tools that deal with binaries (e.g. objdump) operate in unix
binary mode and tools that deal with text files (e.g. bash) operate in
text mode.
Some people push the notion of globally setting the default processing
mode to binary via mount point options or by setting the CYGWIN32
environment variable. But that creates a different problem. In
binary mode, the program receives all of the data in the file, including
a \r. Since the programs will no longer deal with these properly for
you, you would have to remove the \r from the relevant text files,
especially scripts and startup resource files. This is a porter "cop
out", forcing the user to deal with the \r for the porter.
It is rather easy for the porter to fix the source code by supplying the
appropriate file processing mode switches to the open/fopen functions.
Treat all text files as text and treat all binary files as binary.
To be specific, you can select binary mode by adding @code{O_BINARY} to
the second argument of an @code{open} call, or @code{"b"} to second
argument of an @code{fopen} call. You can also call @code{setmode (fd,
O_BINARY)}.
Note that because the open/fopen switches are defined by ANSI, they
exist under most flavors of Unix; open/fopen will just ignore the switch
since they have no meaning to UNIX.
Also note that @code{lseek} only works in binary mode.
Explanation adapted from mailing list email by Earnie Boyd
<earnie_boyd@@yahoo.com>.
@subsection Is the Cygwin library multi-thread-safe?
No.
There is an experimental configure option (--enable-threadsafe), which
allows you to build a DLL with some additional "thread safety" but there
are no guarantees that this is 100% operational. This option also
enables limited "POSIX thread" support. See the file cygwin.din for the
list of POSIX thread functions provided.
Cygnus does not distribute a DLL with this option enabled, and,
currently, has no plans to do so.
Cygwin is not multi-thread-safe because:
1) Newlib (out libc/libm) isn't reentrant (although it almost is).
This would have to be fixed or we would have to switch to a libc/libm
that is reentrant.
2) Cygwin locks shared memory areas (shared by multiple processes),
but the per-process data is not locked. Thus, different threads in a
multi-threaded application would have access to it and give rise to
nasty race-conditions.
The Mingw package (what you get when you invoke gcc with -mno-cygwin) is
multi-thread-safe because that configuration doesn't use Cygwin or
newlib. Instead, it uses Microsoft libraries which are
multi-thread-safe for the most part. So as long as the programmer
avoids Microsoft APIs that aren't multi-thread-safe (most are ok), they
should be fine.
@subsection Why is some functionality only supported in Windows NT?
Windows 9x: n.
32 bit extensions and a graphical shell for a 16 bit patch to an
8 bit operating system originally coded for a 4 bit microprocessor,
written by a 2 bit company that can't stand 1 bit of competition.
But seriously, Windows 9x lacks most of the security-related calls and
has several other deficiencies with respect to its version of the Win32
API. See the calls.texinfo document for more information as to what
is not supported in Win 9x.
@subsection How is fork() implemented?
Cygwin fork() essentially works like a non-copy on write version
of fork() (like old Unix versions used to do). Because of this it
can be a little slow. In most cases, you are better off using the
spawn family of calls if possible.
Here's how fork works as of beta 18:
Parent initializes a space in the Cygwin process
table for child. Parent creates child suspended using Win32 CreateProcess
call, giving the same path it was invoked with itself. Parent
calls setjmp to save its own context and then sets a pointer to this
in the Cygwin shared memory area (shared among all Cygwin tasks).
Parent fills in the childs .data and .bss subsections by copying from
its own address space into the suspended child's address space.
Parent then starts the child. Parent waits on mutex for child to get
to safe point. Child starts and discovers if has been forked and
then longjumps using the saved jump buffer. Child sets mutex parent
is waiting on and then blocks on another mutex waiting for parent to
fill in its stack and heap. Parent notices child is in safe area,
copies stack and heap from itself into child, releases the mutex
the child is waiting on and returns from the fork call. Child wakes
from blocking on mutex, recreates any mmapped areas passed to it via
shared area and then returns from fork itself.
@subsection How does wildcarding (globbing) work?
If an application using CYGWIN.DLL starts up, and can't find the
@code{PID} environment variable, it assumes that it has been started
from the a DOS style command prompt. This is pretty safe, since the
rest of the tools (including bash) set PID so that a new process knows
what PID it has when it starts up.
If the DLL thinks it has come from a DOS style prompt, it runs a
`globber' over the arguments provided on the command line. This means
that if you type @code{LS *.EXE} from DOS, it will do what you might
expect.
Beware: globbing uses @code{malloc}. If your application defines
@code{malloc}, that will get used. This may do horrible things to you.
@subsection How do symbolic links work?
CYGWIN.DLL generates link files with a magic header. When
you open a file or directory that is a link to somewhere else, it
opens the file or directory listed in the magic header. Because we
don't want to have to open every referenced file to check symlink
status, Cygwin marks symlinks with the system attribute. Files
without the system attribute are not checked. Because remote samba
filesystems do not enable the system attribute by default, symlinks do
not work on network drives unless you explicitly enable this
attribute.
@subsection Why do some files, which are not executables have the 'x' type.
When working out the unix-style attribute bits on a file, the library
has to fill out some information not provided by the WIN32 API.
It guesses that files ending in .exe and .bat are executable, as are
ones which have a "#!" as their first characters.
@subsection How secure is Cygwin in a multi-user environment?
Cygwin is not secure in a multi-user environment. For
example if you have a long running daemon such as "inetd"
running as admin while ordinary users are logged in, or if
you have a user logged in remotely while another user is logged
into the console, one cygwin client can trick another into
running code for it. In this way one user may gain the
priveledge of another cygwin program running on the machine.
This is because cygwin has shared state that is accessible by
all processes.
(Thanks to Tim Newsham (newsham@@lava.net) for this explanation).
@subsection How do the net-related functions work?
The network support in Cygwin is supposed to provide the Unix API, not
the Winsock API.
There are differences between the semantics of functions with the same
name under the API.
E.g., the select system call on Unix can wait on a standard file handles
and handles to sockets. The select call in winsock can only wait on
sockets. Because of this, cygwin.dll does a lot of nasty stuff behind
the scenes, trying to persuade various winsock/win32 functions to do what
a Unix select would do.
If you are porting an application which already uses Winsock, then
using the net support in Cygwin is wrong.
But you can still use native Winsock, and use Cygwin. The functions
which cygwin.dll exports are called 'cygwin_<name>'. There
are a load of defines which map the standard Unix names to the names
exported by the dll -- check out include/netdb.h:
@example
..etc..
void cygwin_setprotoent (int);
void cygwin_setservent (int);
void cygwin_setrpcent (int);
..etc..
#ifndef __INSIDE_CYGWIN_NET__
#define endprotoent cygwin_endprotoent
#define endservent cygwin_endservent
#define endrpcent cygwin_endrpcent
..etc..
@end example
The idea is that you'll get the Unix->Cygwin mapping if you include
the standard Unix header files. If you use this, you won't need to
link with libwinsock.a - all the net stuff is inside the dll.
The mywinsock.h file is a standard winsock.h which has been hacked to
remove the bits which conflict with the standard Unix API, or are
defined in other headers. E.g., in mywinsock.h, the definition of
struct hostent is removed. This is because on a Unix box, it lives in
netdb. It isn't a good idea to use it in your applications.
As of the b19 release, this information may be slightly out of date.
@subsection I don't want Unix sockets, how do I use normal Win32 winsock?
To use the vanilla Win32 winsock, you just need to #define Win32_Winsock
and #include "windows.h" at the top of your source file(s). You'll also
want to add -lwsock32 to the compiler's command line so you link against
libwsock32.a.
@subsection What version numbers are associated with Cygwin?
There is a cygwin.dll major version number that gets incremented
every time we make a new Cygwin release available. This
corresponds to the name of the release (e.g. beta 19's major
number is "19"). There is also a cygwin.dll minor version number. If
we release an update of the library for an existing release, the minor
number would be incremented.
There are also Cygwin API major and minor numbers. The major number
tracks important non-backward-compatible interface changes to the API.
An executable linked with an earlier major number will not be compatible
with the latest DLL. The minor number tracks significant API additions
or changes that will not break older executables but may be required by
newly compiled ones.
Then there is a shared memory region compatibity version number. It is
incremented when incompatible changes are made to the shared memory
region or to any named shared mutexes, semaphores, etc.
Finally there is a mount point registry version number which keeps track
of non-backwards-compatible changes to the registry mount table layout.
This has been "B15.0" since the beta 15 release.
@subsection Why isn't _timezone set correctly?
Did you explicitly call tzset() before checking the value of _timezone?
If not, you must do so.
@section Programming Questions
@subsection Why is gcc failing?
If the error is "gcc: installation problem, cannot exec `cpp':
No such file or directory", the GCC_EXEC_PREFIX environment variable
hasn't been set correctly. The current release does not need
GCC_EXEC_PREFIX set -- it should be able to find cpp regardless of the
install location. But if you have it set incorrectly, you may still
see this message.
@subsection Why can't bison find bison.simple or bison.hairy?
If you are getting a warning to this effect, you need to set
the BISONLIB environment variable. The value should be the directory
in which bison.simple and bison.hairy are installed. This will be
the path leading up to and including the @code{share} directory of
the top-level of the binary distributions. For example, on some
systems, you would want to set it to @code{C:/cygnus/cygwin-b20/share}.
@subsection Why is make behaving badly?
Starting with the beta 19 release, make defaults to a win32 mode in
which backslashes in filenames are permitted and cmd.exe/command.com
is used as the sub-shell. In this mode, escape characters aren't
allowed among other restrictions. For this reason, you must set
the environment variable MAKE_MODE to UNIX to run make on ordinary Unix
Makefiles. Here is the full scoop:
MAKE_MODE selects between native Win32 make mode (the default) and
a Unix mode where it behaves like a Unix make. The Unix mode does
allow specifying Win32-style paths but only containing forward slashes
as the path separator. The path list separator character is a colon
in Unix mode.
Win32 mode expects path separators to be either / or \. Thus no
Unix-style \s as escape are allowed. Win32 mode also uses
cmd.exe/command.com as the subshell which means "copy" and "del"
(and other shell builtins) will work. The path list separator
character is semi-colon in Win32 mode. People who want an nmake-like
make might want to use this mode but no one should expect Unix
Makefiles to compile in this mode. That is why the default b19
install sets MAKE_MODE to UNIX.
@subsection Why the undefined reference to "WinMain@@16"?
Try adding an empty main() function to one of your sources.
@subsection How do I use Win32 API calls?
It's pretty simple actually. Cygwin tools require that you explicitly
link the import libraries for whatever Win32 API functions that you
are going to use, with the exception of kernel32, which is linked
automatically (because the startup and/or built-in code uses it).
For example, to use graphics functions (GDI) you must link
with gdi32 like this:
gcc -o foo.exe foo.o bar.o -lgdi32
or (compiling and linking in one step):
gcc -o foo.exe foo.c bar.c -lgdi32
The following libraries are available for use in this way:
advapi32 largeint ole32 scrnsave vfw32
cap lz32 oleaut32 shell32 win32spl
comctl32 mapi32 oledlg snmp winmm
comdlg32 mfcuia32 olepro32 svrapi winserve
ctl3d32 mgmtapi opengl32 tapi32 winspool
dlcapi mpr penwin32 th32 winstrm
gdi32 msacm32 pkpd32 thunk32 wow32
glaux nddeapi rasapi32 url wsock32
glu32 netapi32 rpcdce4 user32 wst
icmp odbc32 rpcndr uuid
imm32 odbccp32 rpcns4 vdmdbg
kernel32 oldnames rpcrt4 version
The regular setup allows you to use the option -mwindows on the
command line to include a set of the basic libraries (and also
make your program a GUI program instead of a console program),
including user32, gdi32 and, IIRC, comdlg32.
Note that you should never include -lkernel32 on your link line
unless you are invoking ld directly. Do not include the same import
library twice on your link line. Finally, it is a good idea to
put import libraries last on your link line, or at least after
all the object files and static libraries that reference them.
The first two are related to problems the linker has (as of b18 at least)
when import libraries are referenced twice. Tables get messed up and
programs crash randomly. The last point has to do with the fact that
gcc processes the files listed on the command line in sequence and
will only resolve references to libraries if they are given after
the file that makes the reference.
@subsection How do I compile a Win32 executable that doesn't use Cygwin?
The -mno-cygwin flag to gcc makes gcc link against standard Microsoft
DLLs instead of Cygwin. This is desirable for native Windows programs
that don't need a UNIX emulation layer.
@subsection How do I make the console window go away?
The default during compilation is to produce a console application.
It you are writing a GUI program, you should either compile with
-mwindows as explained above, or add the string
"-Wl,--subsystem,windows" to the GCC commandline.
@subsection Why does make complain about a "missing separator"?
This problem usually occurs as a result of someone editing a Makefile
with a text editor that replaces tab characters with spaces. Command
lines must start with tabs.
@subsection Why can't we redistribute Microsoft's Win32 headers?
Subsection 2.d.f of the `Microsoft Open Tools License agreement' looks like
it says that can not "permit further redistribution of the
Redistributables to their end users". We take this to mean that we can
give them to you, but you can't give them to anyone else, which is
something that Cygnus can't agree to. Fortunately, we have our own
Win32 headers which are pretty complete.
@subsection How do I link against .lib files?
1. Build a C file with a function table. Put all functions you intend
to use in that table. This forces the linker to include all the object
files from the .lib. Maybe there is an option to force LINK.EXE to
include an object file.
2. Build a dummy 'LibMain'.
3. Build a .def with all the exports you need.
4. Link with your .lib using link.exe.
or
1. Extract all the object files from the .lib using LIB.EXE.
2. Build a dummy C file referencing all the functions you need, either
with a direct call or through an initialized function pointer.
3. Build a dummy LibMain.
4. Link all the objects with this file+LibMain.
5. Write a .def.
6. Link.
You can use these methods to use MSVC (and many other runtime libs)
with Cygwin development tools.
Note that this is a lot of work (half a day or so), but much less than
rewriting the runtime library in question from specs...
(thanks to Jacob Navia (root@@jacob.remcomp.fr) for this explanation)
@subsection How do I rebuild the tools on my NT box?
Assuming that you have the src installed as /src, will build in
the directory /obj, and want to install the tools in /install:
@example
bash
cd /obj
/src/configure --prefix=/install -v > configure.log 2>&1
make > make.log 2>&1
make install > install.log 2>&1
@end example
@subsection How can I compile a powerpc NT toolchain?
Unfortunately, this will be difficult. It hasn't been built for
some time (late 1996) since Microsoft has dropped development of
powerpc NT. Exception handling/signals support semantics/args have been
changed for x86 and not updated for ppc so the ppc specific support would
have to be rewritten. We don't know of any other incompatibilities.
Please send us patches if you do this work!
@subsection How can I compile an Alpha NT toolchain?
We have not ported the tools to Alpha NT and do not have plans to
do so at the present time. We would be happy to add support
for Alpha NT if someone contributes the changes to us.
@subsection How can I adjust the heap/stack size of an application?
Pass heap/stack linker arguments to gcc. To create foo.exe with
a heap size of 1024 and a stack size of 4096, you would invoke
gcc as:
@code{gcc -Wl,--heap,1024,--stack,4096 -o foo foo.c}
@subsection How can I find out which dlls are needed by an executable?
objdump -p provides this information.
@subsection How do I build a DLL?
There's documentation that explains the process on the main Cygwin
project web page (http://sourceware.cygnus.com/cygwin/).
@subsection How can I set a breakpoint at MainCRTStartup?
Set a breakpoint at *0x401000 in gdb and then run the program in
question.
@subsection How can I build a relocatable dll?
You must execute the following sequence of five commands, in this
order:
@example
$(LD) -s --base-file BASEFILE --dll -o DLLNAME OBJS LIBS -e ENTRY
$(DLLTOOL) --as=$(AS) --dllname DLLNAME --def DEFFILE \
--base-file BASEFILE --output-exp EXPFILE
$(LD) -s --base-file BASEFILE EXPFILE -dll -o DLLNAME OBJS LIBS -e ENTRY
$(DLLTOOL) --as=$(AS) --dllname DLLNAME --def DEFFILE \
--base-file BASEFILE --output-exp EXPFILE
$(LD) EXPFILE --dll -o DLLNAME OBJS LIBS -e ENTRY
@end example
In this example, $(LD) is the linker, ld.
$(DLLTOOL) is dlltool.
$(AS) is the assembler, as.
DLLNAME is the name of the DLL you want to create, e.g., tcl80.dll.
OBJS is the list of object files you want to put into the DLL.
LIBS is the list of libraries you want to link the DLL against. For
example, you may or may not want -lcygwin. You may want -lkernel32.
Tcl links against -lcygwin -ladvapi32 -luser32 -lgdi32 -lcomdlg32
-lkernel32.
DEFFILE is the name of your definitions file. A simple DEFFILE would
consist of ``EXPORTS'' followed by a list of all symbols which should
be exported from the DLL. Each symbol should be on a line by itself.
Other programs will only be able to access the listed symbols.
BASEFILE is a temporary file that is used during this five stage
process, e.g., tcl.base.
EXPFILE is another temporary file, e.g., tcl.exp.
ENTRY is the name of the function which you want to use as the entry
point. This function should be defined using the WINAPI attribute,
and should take three arguments:
int WINAPI startup (HINSTANCE, DWORD, LPVOID)
This means that the actual symbol name will have an appended @@12, so if
your entry point really is named @samp{startup}, the string you should
use for ENTRY in the above examples would be @samp{startup@@12}.
If your DLL calls any Cygwin API functions, the entry function will need
to initialize the Cygwin impure pointer. You can do that by declaring
a global variable @samp{_impure_ptr}, and then initializing it in the
entry function. Be careful not to export the global variable
@samp{_impure_ptr} from your DLL; that is, do not put it in DEFFILE.
@example
/* This is a global variable. */
struct _reent *_impure_ptr;
extern struct _reent *__imp_reent_data;
int entry (HINSTANT hinst, DWORD reason, LPVOID reserved)
@{
_impure_ptr = __imp_reent_data;
/* Whatever else you want to do. */
@}
@end example
You may put an optional `--subsystem windows' on the $(LD) lines. The
Tcl build does this, but I admit that I no longer remember whether
this is important. Note that if you specify a --subsytem <x> flag to ld,
the -e entry must come after the subsystem flag, since the subsystem flag
sets a different default entry point.
You may put an optional `--image-base BASEADDR' on the $(LD) lines.
This will set the default image base. Programs using this DLL will
start up a bit faster if each DLL occupies a different portion of the
address space. Each DLL starts at the image base, and continues for
whatever size it occupies.
Now that you've built your DLL, you may want to build a library so
that other programs can link against it. This is not required: you
could always use the DLL via LoadLibrary. However, if you want to be
able to link directly against the DLL, you need to create a library.
Do that like this:
$(DLLTOOL) --as=$(AS) --dllname DLLNAME --def DEFFILE --output-lib LIBFILE
$(DLLTOOL), $(AS), DLLNAME, and DEFFILE are the same as above. Make
sure you use the same DLLNAME and DEFFILE, or things won't work right.
LIBFILE is the name of the library you want to create, e.g.,
libtcl80.a. You can then link against that library using something
like -ltcl80 in your linker command.
@subsection How can I debug what's going on?
You can debug your application using @code{gdb}. Make sure you
compile it with the -g flag! If your application calls functions in
MS dlls, gdb will complain about not being able to load debug information
for them when you run your program. This is normal since these dlls
don't contain debugging information (and even if they did, that debug
info would not be compatible with gdb).
@subsection Can I use a system trace mechanism instead?
Yes. If you have a newer cygwin with the @code{strace.exe} program,
@code{strace} can run other cygwin programs with various debug and
trace messages enabled. For information on using the @code{strace}
program, see the Cygwin User's Guide or the file
@code{winsup/utils/utils/sgml}.
If you have an older cygwin, you can set the <CODE>STRACE</CODE>
environment variable to <CODE>1</CODE>, and get a whole load of debug
information on your screen whenever a Cygwin app runs. This is an
especially useful tool to use when tracking bugs down inside the
Cygwin library. <CODE>STRACE</CODE> can be set to different values to
achieve different amounts of granularity. You can set it to
<CODE>0x10</CODE> for information about syscalls or <CODE>0x800</CODE>
for signal/process handling-related info, to name two. The strace
mechanism is well documented in the Cygwin library sources in the file
<CODE>winsup/include/sys/strace.h</CODE>.
@subsection The linker complains that it can't find something.
A common error is to put the library on the command line before
the thing that needs things from it.
This is wrong @code{gcc -lstdc++ hello.cc}.
This is right @code{gcc hello.cc -lstdc++}.
@subsection I use a function I know is in the API, but I still get a link
error.
The function probably isn't declared in the header files, or
the UNICODE stuff for it isn't filled in.
@subsection Can you make DLLs that are linked against libc ?
Yes.
@subsection Where is malloc.h?
Include stdlib.h instead of malloc.h.
@subsection Can I use my own malloc?
If you define a function called @code{malloc} in your own code, and link
with the DLL, the DLL @emph{will} call your @code{malloc}. Needless to
say, you will run into serious problems if your malloc is buggy.
If you run any programs from the DOS command prompt, rather than from in
bash, the DLL will try and expand the wildcards on the command line.
This process uses @code{malloc} @emph{before} your main line is started.
If you have written your own @code{malloc} to need some initialization
to occur after @code{main} is called, then this will surely break.
@subsection Can I mix objects compiled with msvc++ and gcc?
Yes, but only if you are combining C object files. MSVC C++ uses a
different mangling scheme than GNU C++, so you will have difficulties
combining C++ objects.
@subsection Can I use the gdb debugger to debug programs built by VC++?
No, not for full (high level source language) debugging.
The Microsoft compilers generate a different type of debugging
symbol information, which gdb does not understand.
However, the low-level (assembly-type) symbols generated by
Microsoft compilers are coff, which gdb DOES understand.
Therefore you should at least be able to see all of your
global symbols; you just won't have any information about
data types, line numbers, local variables etc.
@subsection Where can I find info on x86 assembly?
CPU reference manuals for Intel's current chips are available in
downloadable PDF form on Intel's web site:
@file{http://developer.intel.com/design/pro/manuals/}
@subsection Shell scripts aren't running properly from my makefiles?
You need to have . (dot) in your $PATH. You should NOT need to add
/bin/sh in front of each and every shell script invoked in your
Makefiles.
@subsection What preprocessor do I need to know about?
We use _WIN32 to signify access to the Win32 API and __CYGWIN__ for
access to the Cygwin environment provided by the dll.
We chose _WIN32 because this is what Microsoft defines in VC++ and
we thought it would be a good idea for compatibility with VC++ code
to follow their example. We use _MFC_VER to indicate code that should
be compiled with VC++.
@subsection Where can I get f77 and objc components for B20 EGCS 1.1?
B20-compatible versions of the f77 and objc components are available
from @file{http://www.xraylith.wisc.edu/~khan/software/gnu-win32/}.
@subsection How should I port my Unix GUI to Windows?
There are two basic strategies for porting Unix GUIs to Windows.
The first is to use a portable graphics library such as tcl/tk, X11, or
V (and others?). Typically, you will end up with a GUI on Windows that
requires some runtime support. With tcl/tk, you'll want to include the
necessary library files and the tcl/tk DLLs. In the case of X11, you'll
need everyone using your program to have an X11 server installed.
The second method is to rewrite your GUI using Win32 API calls (or MFC
with VC++). If your program is written in a fairly modular fashion, you
may still want to use Cygwin if your program contains a lot of shared
(non-GUI-related) code. That way you still gain some of the portability
advantages inherent in using Cygwin.
@subsection Why not use DJGPP ?
DJGPP is a similar idea, but for DOS instead of Win32. DJGPP uses a
"DOS extender" to provide a more reasonable operating interface for its
applications. The Cygwin toolset doesn't have to do this since all of
the applications are native WIN32. Applications compiled with the
Cygwin tools can access the Win32 API functions, so you can write
programs which use the Windows GUI.
You can get more info on DJGPP by following
@file{http://www.delorie.com/}.
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