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2023-02-23liblzma: Avoid null pointer + 0 (undefined behavior in C).Lasse Collin2-3/+16
In the C99 and C17 standards, section 6.5.6 paragraph 8 means that adding 0 to a null pointer is undefined behavior. As of writing, "clang -fsanitize=undefined" (Clang 15) diagnoses this. However, I'm not aware of any compiler that would take advantage of this when optimizing (Clang 15 included). It's good to avoid this anyway since compilers might some day infer that pointer arithmetic implies that the pointer is not NULL. That is, the following foo() would then unconditionally return 0, even for foo(NULL, 0): void bar(char *a, char *b); int foo(char *a, size_t n) { bar(a, a + n); return a == NULL; } In contrast to C, C++ explicitly allows null pointer + 0. So if the above is compiled as C++ then there is no undefined behavior in the foo(NULL, 0) call. To me it seems that changing the C standard would be the sane thing to do (just add one sentence) as it would ensure that a huge amount of old code won't break in the future. Based on web searches it seems that a large number of codebases (where null pointer + 0 occurs) are being fixed instead to be future-proof in case compilers will some day optimize based on it (like making the above foo(NULL, 0) return 0) which in the worst case will cause security bugs. Some projects don't plan to change it. For example, gnulib and thus many GNU tools currently require that null pointer + 0 is defined: https://lists.gnu.org/archive/html/bug-gnulib/2021-11/msg00000.html https://www.gnu.org/software/gnulib/manual/html_node/Other-portability-assumptions.html In XZ Utils null pointer + 0 issue should be fixed after this commit. This adds a few if-statements and thus branches to avoid null pointer + 0. These check for size > 0 instead of ptr != NULL because this way bugs where size > 0 && ptr == NULL will likely get caught quickly. None of them are in hot spots so it shouldn't matter for performance. A little less readable version would be replacing ptr + offset with offset != 0 ? ptr + offset : ptr or creating a macro for it: #define my_ptr_add(ptr, offset) \ ((offset) != 0 ? ((ptr) + (offset)) : (ptr)) Checking for offset != 0 instead of ptr != NULL allows GCC >= 8.1, Clang >= 7, and Clang-based ICX to optimize it to the very same code as ptr + offset. That is, it won't create a branch. So for hot code this could be a good solution to avoid null pointer + 0. Unfortunately other compilers like ICC 2021 or MSVC 19.33 (VS2022) will create a branch from my_ptr_add(). Thanks to Marcin Kowalczyk for reporting the problem: https://github.com/tukaani-project/xz/issues/36
2019-06-23liblzma: Fix warnings from -Wsign-conversion.Lasse Collin1-1/+1
Also, more parentheses were added to the literal_subcoder macro in lzma_comon.h (better style but no functional change in the current usage).
2016-11-21liblzma: Avoid multiple definitions of lzma_coder structures.Lasse Collin4-19/+28
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
2012-07-17liblzma: Make the use of lzma_allocator const-correct.Lasse Collin6-12/+14
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.
2011-05-17Add underscores to attributes (__attribute((__foo__))).Lasse Collin1-1/+1
2010-05-26Rename MIN() and MAX() to my_min() and my_max().Lasse Collin1-1/+1
This should avoid some minor portability issues.
2009-11-14Fix a design error in liblzma API.Lasse Collin4-7/+20
Originally the idea was that using LZMA_FULL_FLUSH with Stream encoder would read the filter chain from the same array that was used to intialize the Stream encoder. Since most apps wouldn't use LZMA_FULL_FLUSH, most apps wouldn't need to keep the filter chain available after initializing the Stream encoder. However, due to my mistake, it actually required keeping the array always available. Since setting the new filter chain via the array used at initialization time is not a nice way to do it for a couple of reasons, this commit ditches it and introduces lzma_filters_update(). This new function replaces also the "persistent" flag used by LZMA2 (and to-be-designed Subblock filter), which was also an ugly thing to do. Thanks to Alexey Tourbin for reminding me about the problem that Stream encoder used to require keeping the filter chain allocated.
2009-06-30Build system fixesLasse Collin2-28/+23
Don't use libtool convenience libraries to avoid recently discovered long-standing subtle but somewhat severe bugs in libtool (at least 1.5.22 and 2.2.6 are affected). It was found when porting XZ Utils to Windows <http://lists.gnu.org/archive/html/libtool/2009-06/msg00070.html> but the problem is significant also e.g. on GNU/Linux. Unless --disable-shared is passed to configure, static library built from a set of convenience libraries will contain PIC objects. That is, while libtool builds non-PIC objects too, only PIC objects will be used from the convenience libraries. On 32-bit x86 (tested on mobile XP2400+), using PIC instead of non-PIC makes the decompressor 10 % slower with the default CFLAGS. So while xz was linked against static liblzma by default, it got the slower PIC objects unless --disable-shared was used. I tend develop and benchmark with --disable-shared due to faster build time, so I hadn't noticed the problem in benchmarks earlier. This commit also adds support for building Windows resources into liblzma and executables.
2009-06-26Fix @variables@ to $(variables) in Makefile.am files.Lasse Collin1-2/+2
Fix the ordering of libgnu.a and LTLIBINTL on the linker command line and added missing LTLIBINTL to tests/Makefile.am.
2009-04-13Put the interesting parts of XZ Utils into the public domain.Lasse Collin8-80/+24
Some minor documentation cleanups were made at the same time.
2008-12-01Added lzma_delta_coder_memusage() which also validatesLasse Collin8-39/+75
the options.
2008-09-27Some API changes, bug fixes, cleanups etc.Lasse Collin4-11/+11
2008-09-13Renamed constants:Lasse Collin3-3/+3
- LZMA_VLI_VALUE_MAX -> LZMA_VLI_MAX - LZMA_VLI_VALUE_UNKNOWN -> LZMA_VLI_UNKNOWN - LZMA_HEADER_ERRRO -> LZMA_OPTIONS_ERROR
2008-08-28Sort of garbage collection commit. :-| Many things are stillLasse Collin7-0/+407
broken. API has changed a lot and it will still change a little more here and there. The command line tool doesn't have all the required changes to reflect the API changes, so it's easy to get "internal error" or trigger assertions.