Summary:
Issue reported by @ryandesign and @MarcusCalhoun-Lopez.
CMake doesn't support spaces in flags. This caused older versions of gcc to
ignore the unknown flag "-z noexecstack" on MacOS since it was interpreted as a
single flag, not two separate flags. Then, during compilation it was treated as
"-z" "noexecstack", which was correctly forwarded to the linker. But the MacOS
linker does not support `-z noexecstack` so compilation failed.
The fix is to use `-Wl,-z,noexecstack`. This is never misinterpreted by a
compiler. However, not all compilers support this syntax to forward flags to the
linker. To fix this issue, we check if all the relevant `noexecstack` flags have
been successfully set, and if they haven't we disable assembly.
See also PR#4056 and PR#4061. I decided to go a different route because this is
simpler. It might not successfully set these flags on some compilers, but in that
case it also disables assembly, so they aren't required.
Test Plan:
```
mkdir build-cmake
cmake ../build/cmake/CMakeLists.txt
make -j
```
See that the linker flag is successfully detected & that assembly is enabled.
Run the same commands on MacOS which doesn't support `-Wl,-z,noexecstack` and see
that everything compiles and that `LD_FLAG_WL_Z_NOEXECSTACK` and
`ZSTD_HAS_NOEXECSTACK` are both false.
This fixes compilation with clang-cl on Windows. There
is a bug in cmake so that check_linker_flag() doesn't give
the correct result when using link.exe/lld-link.exe.
Details in CMake's gitlab: https://gitlab.kitware.com/cmake/cmake/-/issues/22023Fixes#3522
fix#3500
CMake 3.18 or later was required by #3392. Because it uses
`CheckLinkerFlag`. But requiring CMake 3.18 or later is a bit
aggressive. Because Ubuntu 20.04 LTS still uses CMake 3.16.3:
https://packages.ubuntu.com/search?keywords=cmake
This change disables `-z noexecstack` check with old CMake. This will
not break any existing users. Because users who need `-z noexecstack`
must already use CMake 3.18 or later.
With this patch the pkg-config generation when using the CMake build
system is improved in the following ways:
- Libs.private is now filled when needed
- The JoinPaths module is now used to join paths, leading to simpler
code
- The .pc file is always generated, regardless of the platform, as it
can also be consumed on Windows
Here's how the .pc file is affected by these changes, in comparison to
the one generated with the official Makefiles:
$ diff -s lib/libzstd.pc build/cmake/build-old/lib/libzstd.pc
15c15
< Libs.private: -pthread
---
> Libs.private:
$ diff -s lib/libzstd.pc build/cmake/build-new/lib/libzstd.pc
Files lib/libzstd.pc and build/cmake/build-new/lib/libzstd.pc are
identical
Automatically extract version information
from the zstd.h file. Use naming of variables
consisent with modern cmake and https://semver.org/
(Semantic Versioning 2.0.0, MAJOR, MINOR, PATCH)
Modern versions of cmake provide consistent
paradigms for configuring project external
interface values.
This set of changes provide a back port of
some of cmake 3+ paradigms back to cmake 2.8.9.
Set and allow use of the current cmake policies
for newer versions of cmake when available to
allow for modern compiler features to be
utilized when available.
NOTE: The intent is that future modifications to
cmake will enable (conditional on cmake version support)
the ability to support modern linkage, and target
export mechanisms. Those future changes will
make incorporating zstd into other packages
much easier.
This patch also allows the more rigourous error
checking of commmon cmake errors to be preformed
by cmake (i.e. more stringent syntax checking and
create errors for common hard to find misuses of
cmake variables).
This patch also provides support for modern
compiler support options by cmake (like
enabling interprocedural optimization
if link time optimizations are known to be supported
by the compiler envirionment. IPO can be supported
by setting the CMAKE_INTERPROCEDURAL_OPTIMIZATION variable
for newer versions of cmake.
When compiling without c++ enabled, some variables are not present.
This is a check enforced in recent Cmake versions.
CMake Error at CMakeModules/AddZstdCompilationFlags.cmake:54 (list):
list sub-command REMOVE_DUPLICATES requires list to be present.
Call Stack (most recent call first):
CMakeLists.txt:53 (ADD_ZSTD_COMPILATION_FLAGS)
Ancient versions of CMake required else(), endif(), and similar block
termination commands to have arguments matching the command starting the block.
This is no longer the preferred style.
