On ARM64, support for fast unaligned memory access was autodetected by
checking if __ARM_FEATURE_UNALIGNED is defined. However, at least GCC
versions up to 15.2.0 define the macro even when -mstrict-align has
been specified. Thus, autodetection with GCC doesn't work correctly,
and binaries built using -mstrict-align can be much slower than they
need to be, unless the user also passes --disable-unaligned-access
to configure or -DTUKLIB_FAST_UNALIGNED_ACCESS=OFF to cmake.
See the GCC bug:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111555
Workaround the issue by using heuristics with GCC on ARM64.
With Clang, the detection using __ARM_FEATURE_UNALIGNED works.
It also works with GCC on 32-bit ARM.
Fixes: e5f13a66567b ("tuklib_integer: Autodetect support for unaligned access on ARM.")
This still relies on CMAKE_SYSTEM_PROCESSOR. CMake 4.1 added more
CMAKE_<LANG>_COMPILER_ARCHITECTURE_ID values to detect the arch in
a more defined manner, but 4.1 is too new to require for now.
Thanks-to: Li Chenggang <lichenggang@deepin.org>
Closes: https://github.com/tukaani-project/xz/pull/186
Seems that the phrase "add more quotes" from sh/bash scripting
applies to CMake as well. E.g. passing an unquoted list ${FOO}
to a function that expects one argument results in only the
first element of the list being passed as an argument and
the rest get ignored. Adding quotes helps ("${FOO}").
list(INSERT ...) is weird. Inserting an empty string to an empty
variable results in empty list, but inserting it to a non-empty
variable does insert an empty element to the list.
Since INSERT requires at least one element,
"${CMAKE_THREAD_LIBS_INIT}" needs to be quoted in CMakeLists.txt.
It might result in an empty element in the list. It seems to not
matter as empty elements consistently get ignored in that variable.
In fact, calling cmake_check_push_state() and cmake_check_pop_state()
will strip the empty elements from CMAKE_REQUIRED_LIBRARIES!
In addition to quoting fixes, this fixes checks for the cache
variables in tuklib_cpucores.cmake and tuklib_physmem.cmake.
Thanks to Martin Matuška for testing and reporting the problems.
These fixes aren't tested yet but hopefully they soon will be.
This does *NOT* replace the Autotools-based build system in
the foreseeable future. See the comment in the beginning
of CMakeLists.txt.
So far this has been tested only on GNU/Linux but I commit
it anyway to make it easier for others to test. Since I
haven't played much with CMake before, it's likely that
there are things that have been done in a silly or wrong
way and need to be fixed.
