Now memcpy() or GNU C packed structs for unaligned access instead
of type punning. See the comment in this commit for details.
Avoiding type punning with unaligned access is needed to
silence gcc -fsanitize=undefined.
New functions: unaliged_readXXne and unaligned_writeXXne where
XX is 16, 32, or 64.
I should have always known this but I didn't. Here is an example
as a reminder to myself:
int mycopy(void *dest, void *src, size_t n)
{
memcpy(dest, src, n);
return dest == NULL;
}
In the example, a compiler may assume that dest != NULL because
passing NULL to memcpy() would be undefined behavior. Testing
with GCC 8.2.1, mycopy(NULL, NULL, 0) returns 1 with -O0 and -O1.
With -O2 the return value is 0 because the compiler infers that
dest cannot be NULL because it was already used with memcpy()
and thus the test for NULL gets optimized out.
In liblzma, if a null-pointer was passed to memcpy(), there were
no checks for NULL *after* the memcpy() call, so I cautiously
suspect that it shouldn't have caused bad behavior in practice,
but it's hard to be sure, and the problematic cases had to be
fixed anyway.
Thanks to Jeffrey Walton.
Now the widths of the check names is used to adjust the width
of the Check column. This way there no longer is a need to restrict
the widths of the check names to be at most ten terminal-columns.
"xz -dcfv not_an_xz_file" crashed (all four options are
required to trigger it). It caused xz to call
lzma_get_progress(&strm, ...) when no coder was initialized
in strm. In this situation strm.internal is NULL which leads
to a crash in lzma_get_progress().
The bug was introduced when xz started using lzma_get_progress()
to get progress info for multi-threaded compression, so the
bug is present in versions 5.1.3alpha and higher.
Thanks to Filip Palian <Filip.Palian@pjwstk.edu.pl> for
the bug report.
FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION is #defined when liblzma
is being built for fuzz testing.
Most fuzzed inputs would normally get rejected because of incorrect
CRC32 and the actual header decoding code wouldn't get fuzzed.
Disabling CRC32 checks avoids this problem. The fuzzer program
must still use LZMA_IGNORE_CHECK flag to disable verification of
integrity checks of uncompressed data.
It ended up printing an uninitialized char-array when trying to
print the check names (column 7) on the "totals" line.
This also changes the column 12 (minimum xz version) to
50000002 (xz 5.0.0) instead of 0 when there are no valid
input files.
Thanks to kidmin for the bug report.
The 0 got treated specially in a buggy way and as a result
the function did nothing. The API doc said that 0 was supposed
to return LZMA_PROG_ERROR but it didn't.
Now 0 is treated as if 1 had been specified. This is done because
0 is already used to indicate an error from lzma_memlimit_get()
and lzma_memusage().
In addition, lzma_memlimit_set() no longer checks that the new
limit is at least LZMA_MEMUSAGE_BASE. It's counter-productive
for the Index decoder and was actually needed only by the
auto decoder. Auto decoder has now been modified to check for
LZMA_MEMUSAGE_BASE.
It returned LZMA_PROG_ERROR, which was done to avoid zero as
the limit (because it's a special value elsewhere), but using
LZMA_PROG_ERROR is simply inconvenient and can cause bugs.
The fix/workaround is to treat 0 as if it were 1 byte. It's
effectively the same thing. The only weird consequence is
that then lzma_memlimit_get() will return 1 even when 0 was
specified as the limit.
This fixes a very rare corner case in xz --list where a specific
memory usage limit and a multi-stream file could print the
error message "Internal error (bug)" instead of saying that
the memory usage limit is too low.
Only one definition was visible in a translation unit.
It avoided a few casts and temp variables but seems that
this hack doesn't work with link-time optimizations in compilers
as it's not C99/C11 compliant.
Fixes:
http://www.mail-archive.com/xz-devel@tukaani.org/msg00279.html
It's available in glibc (GNU/Linux, GNU/kFreeBSD). It's better
than sysconf(_SC_NPROCESSORS_ONLN) because sched_getaffinity()
gives the number of cores available to the process instead of
the total number of cores online.
As a side effect, this commit fixes a bug on GNU/kFreeBSD where
configure would detect the FreeBSD-specific cpuset_getaffinity()
but it wouldn't actually work because on GNU/kFreeBSD it requires
using -lfreebsd-glue when linking. Now the glibc-specific function
will be used instead.
Thanks to Sebastian Andrzej Siewior for the original patch
and testing.
This is the sane thing to do. The conflict with OpenSSL
on some OSes and especially that the OS-provided versions
can be significantly slower makes it clear that it was
a mistake to have the external SHA-256 support enabled by
default.
Those who want it can now pass --enable-external-sha256 to
configure. INSTALL was updated with notes about OSes where
this can be a bad idea.
The SHA-256 detection code in configure.ac had some bugs that
could lead to a build failure in some situations. These were
fixed, although it doesn't matter that much now that the
external SHA-256 is disabled by default.
MINIX >= 3.2.0 uses NetBSD's libc and thus has SHA256_Init
in libc instead of libutil. Support for the libutil version
was removed.
When optimizing, GCC can reorder code so that an uninitialized
value gets used in a comparison, which makes Valgrind unhappy.
It doesn't happen when compiled with -O0, which I tend to use
when running Valgrind.
Thanks to Rich Prohaska. I remember this being mentioned long
ago by someone else but nothing was done back then.
The patch is quite long but it's mostly about adding new #ifdefs
to omit code when encoders or decoders have been disabled.
This adds two new #defines to config.h: HAVE_ENCODERS and
HAVE_DECODERS.
People shouldn't rely on the presets when decoding raw streams,
but xz uses the presets as the starting point for raw decoder
options anyway.
lzma_encocder_presets.c was renamed to lzma_presets.c to
make it clear it's not used solely by the encoder code.
lzma_index_dup() calls index_dup_stream() which, in case of
an error, calls index_stream_end() to free memory allocated
by index_stream_init(). However, it illogically didn't
actually free the memory. To make it logical, the tree
handling code was modified a bit in addition to changing
index_stream_end().
Thanks to Evan Nemerson for the bug report.
This reverts commit 7a11c4a8e5.
It is a problem when libc has pipe2() but the kernel is too
old to have pipe2() and thus pipe2() fails. In xz it's pointless
to have a fallback for non-functioning pipe2(); it's better to
avoid pipe2() completely.
Thanks to Michael Fox for the bug report.
The sandboxing is used conditionally as described in main.c.
This isn't optimal but it was much easier to implement than
a full sandboxing solution and it still covers the most common
use cases where xz is writing to standard output. This should
have practically no effect on performance even with small files
as fork() isn't needed.
C and locale libraries can open files as needed. This has been
fine in the past, but it's a problem with things like Capsicum.
io_sandbox_enter() tries to ensure that various locale-related
files have been loaded before cap_enter() is called, but it's
possible that there are other similar problems which haven't
been seen yet.
Currently Capsicum is available on FreeBSD 10 and later
and there is a port to Linux too.
Thanks to Loganaden Velvindron for help.
The earlier version compiled but didn't actually work
since sysconf(_SC_PHYS_PAGES) always fails (or so I was told).
Thanks to Ole André Vadla Ravnås for the patch and testing.
In FreeBSD, cpuset_getaffinity() is the preferred way to get
the number of available cores.
Thanks to Rui Paulo for the patch. I edited it slightly, but
hopefully I didn't break anything.
It's a problem at least on OpenBSD which doesn't support
O_NONBLOCK on e.g. /dev/null. I'm not surprised if it's
a problem on other OSes too since this behavior is allowed
in POSIX-1.2008.
The code relying on this behavior was committed in June 2013
and included in 5.1.3alpha released on 2013-10-26. Clearly
the development releases only get limited testing.
I know that soname != app version, but I skip AGE=1
in -version-info to make the soname match the liblzma
version anyway. It doesn't hurt anything as long as
it doesn't conflict with library versioning rules.
This way an invalid filter chain is detected at the Stream
encoder initialization instead of delaying it to the first
call to lzma_code() which triggers the initialization of
the actual filter encoder(s).
This avoids the possibility of "File name too long" when
creating a temp file when the input file name is very long.
This also means that other users on the system can no longer
see the input file names in /tmp (or whatever $TMPDIR is)
since the temporary directory will have a generic name. This
usually doesn't matter since on many systems one can see
the arguments given to all processes anyway.
The number X chars to mktemp where increased from 6 to 10.
Note that with some shells temp files or dirs won't be used at all.
The behavior of grep -ql varies:
- GNU grep behaves like grep -q.
- OpenBSD grep behaves like grep -l.
POSIX doesn't make it 100 % clear what behavior is expected.
Anyway, using both -q and -l at the same time makes no sense
so both options simply should never be used at the same time.
Thanks to Christian Weisgerber.
POSIX supports $< only in inference rules (suffix rules).
Using it elsewhere is a GNU make extension and doesn't
work e.g. with OpenBSD make.
Thanks to Christian Weisgerber for the patch.
Note that this slightly changes how lzma_block_header_decode()
has been documented. Earlier it said that the .version is set
to the lowest required value, but now it says that the .version
field is kept unchanged if possible. In practice this doesn't
affect any old code, because before this commit the only
possible .version was 0.
The Maj macro is used where multiple things are added
together, so making Maj a sum of two expressions allows
some extra freedom for the compiler to schedule the
instructions.
I learned this trick from
<http://www.hackersdelight.org/corres.txt>.
This looks weird because the rotations become sequential,
but it helps quite a bit on both 32-bit and 64-bit x86:
- It requires fewer instructions on two-operand
instruction sets like x86.
- It requires one register less which matters especially
on 32-bit x86.
I hope this doesn't hurt other archs.
I didn't invent this idea myself, but I don't remember where
I saw it first.
This way a branch isn't needed for each operation
to choose between blk0 and blk2, and still the code
doesn't grow as much as it would with full unrolling.
This commit just adds the function. Its uses will be in
separate commits.
This hasn't been tested much yet and it's perhaps a bit early
to commit it but if there are bugs they should get found quite
quickly.
Thanks to Jun I Jin from Intel for help and for pointing out
that string comparison needs to be optimized in liblzma.
Mimic the original grep behavior and return exit_success when
at least one xz compressed file matches given pattern.
Original bugreport:
https://bugzilla.redhat.com/show_bug.cgi?id=1108085
Thanks to Pavel Raiskup for the patch.
This avoids a memzero() call for a newly-allocated memory,
which can be expensive when encoding small streams with
an over-sized dictionary.
To avoid using lzma_alloc_zero() for memory that doesn't
need to be zeroed, lzma_mf.son is now allocated separately,
which requires handling it separately in normalize() too.
Thanks to Vincenzo Innocente for reporting the problem.
In this case "make install" could fail if the man page directory
didn't already exist at the destination. If it did exist, a
dangling symlink was created there. Now the link is omitted
instead. This isn't the best fix but it's better than the old
behavior.
I don't know the details but I have an impression that there's
no problem in practice if using GCC since people have built xz
with GCC (without patching xz), but renaming the variable cannot
hurt either.
Thanks to Mark Ashley.
Previously, --block-list and --block-size only worked together
in threaded mode. Boundaries are specified by --block-list, but
--block-size specifies the maximum size for a Block. Now this
works in single-threaded mode too.
Thanks to James M Leddy for the original patch.
Now if --block-list is used in threaded mode, the encoder
won't need to flush at each Block boundary specified via
--block-list. This improves performance a lot, making
threading helpful with --block-list.
The flush timer was reset after LZMA_FULL_FLUSH but since
LZMA_FULL_BARRIER doesn't flush, resetting the timer is
no longer done.
Now --block-list=SIZES works with in the threaded mode too,
although the performance is still bad due to the use of
LZMA_FULL_FLUSH instead of the new LZMA_FULL_BARRIER.
Now liblzma only uses "mythread" functions and types
which are defined in mythread.h matching the desired
threading method.
Before Windows Vista, there is no direct equivalent to
pthread condition variables. Since this package doesn't
use pthread_cond_broadcast(), pre-Vista threading can
still be kept quite simple. The pre-Vista code doesn't
use anything that wasn't already available in Windows 95,
so the binaries should run even on Windows 95 if someone
happens to care.
Previously it was done in configure, but doing that goes
against the Autoconf manual. Autoconf requires that it is
possible to override e.g. prefix after running configure
and that doesn't work correctly if liblzma.pc is created
by configure.
A potential downside of this change is that now e.g.
libdir in liblzma.pc is a standalone string instead of
being defined via ${prefix}, so if one overrides prefix
when running pkg-config the libdir won't get the new value.
I don't know if this matters in practice.
Thanks to Vincent Torri.
When --flush-timeout=TIMEOUT is used, xz will use
LZMA_SYNC_FLUSH if read() would block and at least
TIMEOUT milliseconds has elapsed since the previous flush.
This can be useful in realtime-like use cases where the
data is simultanously decompressed by another process
(possibly on a different computer). If new uncompressed
input data is produced slowly, without this option xz could
buffer the data for a long time until it would become
decompressible from the output.
If TIMEOUT is 0, the feature is disabled. This is the default.
This commit affects the compression side. Using xz for
the decompression side for the above purpose doesn't work
yet so well because there is quite a bit of input and
output buffering when decompressing.
The --long-help or man page were not updated yet.
The details of this feature may change.
Testing for end of file was no longer correct after full flushing
became possible with --block-size=SIZE and --block-list=SIZES.
There was no bug in practice though because xz just made a few
unneeded zero-byte reads.
This switches units from microseconds to milliseconds.
New clock_gettime(CLOCK_MONOTONIC) will be used if available.
There is still a fallback to gettimeofday().
The man pages of lzmainfo, xzmore, and xzdec had similar
constructs as the man page of xz had before the commit
eb6ca9854b. Eric S. Raymond
didn't mention these man pages in his bug report, but
it's nice to be consistent.
Now both reading and writing should be without
race conditions with signals.
They might still be signal handling issues left.
Signals are blocked during many operations to avoid
EINTR but it may cause problems e.g. if writing to
stderr blocks when trying to display an error message.
It is possible that a signal to set user_abort arrives right
before a blocking system call is made. In this case the call
may block until another signal arrives, while the wanted
behavior is to make xz clean up and exit as soon as possible.
After this commit, the race condition is avoided with the
input side which already uses non-blocking I/O. The output
side still uses blocking I/O and thus has the race condition.
POSIX says that fcntl(fd, F_SETFL, flags) returns -1 on
error and "other than -1" on success. This is how it is
documented e.g. on OpenBSD too. On Linux, success with
F_SETFL is always 0 (at least accorinding to fcntl(2)
from man-pages 3.51).
Due to a wrong variable name, when writing a sparse file
to standard output, *all* file status flags were cleared
(to the extent the operating system allowed it) instead of
only clearing the O_APPEND flag. In practice this worked
fine in the common situations on GNU/Linux, but I didn't
check how it behaved elsewhere.
The original flags were still restored correctly. I still
changed the code to use a separate boolean variable to
indicate when the flags should be restored instead of
relying on a special value in stdout_flags.
Input file can be a FIFO or something else that doesn't
support posix_fadvise() so don't check the return value
even with an assertion. Nothing bad happens if the call
to posix_fadvise() fails.
It is a no-op for now, but if an old xz version is used
together with a newer liblzma that supports something new,
then this check becomes important and will stop the old xz
from trying to parse files that it won't understand.
This affects only "xz -lvv". Normal decompression with xz
already detected if Block Header and Index had mismatched
Uncompressed Size fields. So this just makes "xz -lvv"
show such files as corrupt instead of showing the
Uncompressed Size from Index.
Now the interaction of presets and custom filter chains
is described correctly. Earlier it contradicted itself.
Thanks to DevHC who reported these issues on IRC to me
on 2012-12-14.
There was somewhat illogical behavior when --extreme was
specified and mixed with custom filter chains.
Before this commit, "xz -9 --lzma2 -e" was equivalent
to "xz --lzma2". After it is equivalent to "xz -6e"
(all earlier preset options get forgotten when a custom
filter chain is specified and the default preset is 6
to which -e is applied). I find this less illogical.
This also affects the meaning of "xz -9e --lzma2 -7".
Earlier it was equivalent to "xz -7e" (the -e specified
before a custom filter chain wasn't forgotten). Now it
is "xz -7". Note that "xz -7e" still is the same as "xz -e7".
Hopefully very few cared about this in the first place,
so pretty much no one should even notice this change.
Thanks to Conley Moorhous.
The options are now ordered in the same order as in xz's help
message.
Descriptions were added to the options that are ignored.
I left them in parenthesis even if it looks a bit weird
because I find it easier to spot the ignored vs. non-ignored
options from the list that way.
To avoid false positives when detecting .lzma files,
rare values in dictionary size and uncompressed size fields
were rejected. They will still be rejected if .lzma files
are decoded with lzma_auto_decoder(), but when using
lzma_alone_decoder() directly, such files will now be accepted.
Hopefully this is an OK compromise.
This doesn't affect xz because xz still has its own file
format detection code. This does affect lzmadec though.
So after this commit lzmadec will accept files that xz or
xz-emulating-lzma doesn't.
NOTE: lzma_alone_decoder() still won't decode all .lzma files
because liblzma's LZMA decoder doesn't support lc + lp > 4.
Reported here:
http://sourceforge.net/projects/lzmautils/forums/forum/708858/topic/7068827
This race condition could cause a deadlock if lzma_end() was
called before finishing the encoding. This can happen with
xz with debugging enabled (non-debugging version doesn't
call lzma_end() before exiting).
Use "read" instead of "awk" in xzless to get the version
number of "less". The need for awk was introduced in
the commit db5c1817fa.
Thanks to Ariel P for the patch.
This adds lzma_get_progress() to liblzma and takes advantage
of it in xz.
lzma_get_progress() collects progress information from
the thread-specific structures so that fairly accurate
progress information is available to applications. Adding
a new function seemed to be a better way than making the
information directly available in lzma_stream (like total_in
and total_out are) because collecting the information requires
locking mutexes. It's waste of time to do it more often than
the up to date information is actually needed by an application.
In v4.999.9beta~30 (xzless: Support compressed standard input,
2009-08-09), xzless learned to parse ‘less -V’ output to figure out
whether less is new enough to handle $LESSOPEN settings starting
with “|-”. That worked well for a while, but the version string from
‘less’ versions 448 (June, 2012) is misparsed, producing a warning:
$ xzless /tmp/test.xz; echo $?
/usr/bin/xzless: line 49: test: 456 (GNU regular expressions): \
integer expression expected
0
More precisely, modern ‘less’ lists the regexp implementation along
with its version number, and xzless passes the entire version number
with attached parenthetical phrase as a number to "test $a -gt $b",
producing the above confusing message.
$ less-444 -V | head -1
less 444
$ less -V | head -1
less 456 (no regular expressions)
So relax the pattern matched --- instead of expecting "less <number>",
look for a line of the form "less <number>[ (extra parenthetical)]".
While at it, improve the behavior when no matching line is found ---
instead of producing a cryptic message, we can fall back on a LESSPIPE
setting that is supported by all versions of ‘less’.
The implementation uses "awk" for simplicity. Hopefully that’s
portable enough.
Reported-by: Jörg-Volker Peetz <jvpeetz@web.de>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
There is a tiny risk of causing breakage: If an application
assigns lzma_stream.allocator to a non-const pointer, such
code won't compile anymore. I don't know why anyone would do
such a thing though, so in practice this shouldn't cause trouble.
Thanks to Jan Kratochvil for the patch.
lzma_code() could incorrectly return LZMA_BUF_ERROR if
all of the following was true:
- The caller knows how many bytes of output to expect
and only provides that much output space.
- When the last output bytes are decoded, the
caller-provided input buffer ends right before
the LZMA2 end of payload marker. So LZMA2 won't
provide more output anymore, but it won't know it
yet and thus won't return LZMA_STREAM_END yet.
- A BCJ filter is in use and it hasn't left any
unfiltered bytes in the temp buffer. This can happen
with any BCJ filter, but in practice it's more likely
with filters other than the x86 BCJ.
Another situation where the bug can be triggered happens
if the uncompressed size is zero bytes and no output space
is provided. In this case the decompression can fail even
if the whole input file is given to lzma_code().
A similar bug was fixed in XZ Embedded on 2011-09-19.
When grepping binary files, grep may exit before it has
read all the input. In this case, gzip -q returns 2 (eating
SIGPIPE), but xz and bzip2 show SIGPIPE as the exit status
(e.g. 141). This causes wrong exit status when grepping
xz- or bzip2-compressed binary files.
The fix checks for the special exit status that indicates SIGPIPE.
It uses kill -l which should be supported everywhere since it
is in both SUSv2 (1997) and POSIX.1-2008.
Thanks to James Buren for the bug report.
xzdiff was clobbering the exit status from diff in a case
statement used to analyze the exit statuses from "xz" when
its operands were two compressed files. Save and restore
diff's exit status to fix this.
The bug is inherited from zdiff in GNU gzip and was fixed
there on 2009-10-09.
Thanks to Jonathan Nieder for the patch and
to Peter Pallinger for reporting the bug.
Symbol versioning is enabled by default on GNU/Linux,
other GNU-based systems, and FreeBSD.
I'm not sure how stable this is, so it may need
backward-incompatible changes before the next release.
The idea is that alpha and beta symbols are considered
unstable and require recompiling the applications that
use those symbols. Once a symbol is stable, it may get
extended with new features in ways that don't break
compatibility with older ABI & API.
The mydist target runs validate_map.sh which should
catch some probable problems in liblzma.map. Otherwise
I would forget to update the map file for new releases.
If the operating system libc or other base libraries
provide SHA-256, use that instead of our own copy.
Note that this doesn't use OpenSSL or libgcrypt or
such libraries to avoid creating dependencies to
other packages.
This supports at least FreeBSD, NetBSD, OpenBSD, Solaris,
MINIX, and Darwin. They all provide similar but not
identical SHA-256 APIs; everyone is a little different.
Thanks to Wim Lewis for the original patch, improvements,
and testing.
Now the following works as you would expect:
echo foo | xz > foo.xz
echo bar | xz >> foo.xz
( xz -dc --single-stream ; xz -dc --single-stream ) < foo.xz
Note that it doesn't work if the input is not seekable
or if there is Stream Padding between the concatenated
.xz Streams.
Use gettimeofday() if clock_gettime() isn't available
(e.g. Darwin).
The test for availability of pthread_condattr_setclock()
and CLOCK_MONOTONIC was incorrect. Instead of fixing the
#ifdefs, use an Autoconf test. That way if there exists a
system that supports them but doesn't specify the matching
POSIX #defines, the features will still get detected.
Don't try to use pthread_sigmask() on OpenVMS. It doesn't
have that function.
Guard mythread.h against being #included multiple times.
Reported-by: Diego Elio Pettenò <flameeyes@gentoo.org>
Signed-off-by: Martin Väth <vaeth@mathematik.uni-wuerzburg.de>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Spot candidates by running these commands:
git ls-files |xargs perl -0777 -n \
-e 'while (/\b(then?|[iao]n|i[fst]|but|f?or|at|and|[dt]o)\s+\1\b/gims)' \
-e '{$n=($` =~ tr/\n/\n/ + 1); ($v=$&)=~s/\n/\\n/g; print "$ARGV:$n:$v\n"}'
Thanks to Jim Meyering for the original patch.
This is the simplest method to do threading, which splits
the uncompressed data into blocks and compresses them
independently from each other. There's room for improvement
especially to reduce the memory usage, but nevertheless,
this is a good start.
Empty Block was created if the input buffer was empty.
Empty Block wastes a few bytes of space, but more importantly
it triggers a bug in XZ Utils 5.0.1 and older when trying
to decompress such a file. 5.0.1 and older consider such
files to be corrupt. I thought that no encoder creates empty
Blocks when releasing 5.0.2 but I was wrong.
The biggest problem was that the integrity check type
wasn't validated, and e.g. lzma_easy_buffer_encode()
would create a corrupt .xz Stream if given an unsupported
Check ID. Luckily applications don't usually try to use
an unsupport Check ID, so this bug is unlikely to cause
many real-world problems.
This adds:
- mythread_sync() macro to create synchronized blocks
- mythread_cond structure and related functions
and macros for condition variables with timed
waiting using a relative timeout
- mythread_create() to create a thread with all
signals blocked
Some of these wouldn't need to be inline functions,
but I'll keep them this way for now for simplicity.
For timed waiting on a condition variable, librt is
now required on some systems to use clock_gettime().
configure.ac was updated to handle this.
This is incompatible with the 8.3 support patch made by
Juan Manuel Guerrero. I think this one is nicer, but
I need to get feedback from DOS users before saying
that this is the final version of 8.3 filename support.
Try to avoid overwriting the source file if --force is
used and the generated destination filename refers to
the source file. This can happen with 8.3 filenames where
extra characters are ignored.
If the generated output file refers to a special file
like "con" or "prn", refuse to write to it even if --force
is used.
Lasse Collin
Antoine Cœur
Pavel Raiskup
Ben Boeckel
Jeff Bastian
Jonathan Nieder
Martin Väth