Linker and Llvm toolchain improvements #2301
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…d final build Currently, the linker that is used when performing various cmake checks (check_c_compiler_flag, for example) may be different than the linker that will be used during the actual build. This happens as we currently specify '-fuse-ld' to force the appropriate linker a) after many such checks have already happened and b) in a way which is not automatically propagated to check_c_compiler_flag (and friends). As a result, the toolchain's default linker will generally be used for such checks regardless of which linker was selected in Zephyr. This can lead to a number of surprises when building Zephyr, particularly when building with clang. For example: - If the linker is misconfigured, where the build will fail can vary depending on whether the linker is the toolchain's default. When the configured linker happens to be the toolchain's default, the build (helpfully) fails quickly on the checks for a basic working toochain. When the configured linker isn't the default, the build won't fail until the final link steps. - The build can fail due to issues with a linker other than the one configured by the user in Zephyr. For example, LLVM toolchains without lld will generally fail to build Zephyr (the checks for a basic working toochain will fail) for targets where lld is the default in LLVM even if GNU ld is configured in Zephyr and would otherwise be used in the final build. - Flags which are only added if check_c_compiler_flag (or similar) succeeds may be unexpectedly omitted during the final build if the flag is supported in the configured linker but is unsupported in the toolchain's default linker (as check_c_compiler_flag will test using the default one). Note that this isn't limited to clang--even when we are building with Zephyr's SDK and force ld.bfd, we seem to use the 'ld' variant during the cmake checks (though this generally seems fairly harmless compared to mixing ld/lld or other proprietary linkers). To fix this, ensure the appropriate 'fuse-ld' is set early enough and in such a way that the same linker will be used throughout the entire build. Signed-off-by: Jonathon Penix <[email protected]> Signed-off-by: Torsten Rasmussen <[email protected]> (cherry picked from commit 9fe6c5e)
Zephyr is a bare metal build where standard libs are disabled. This means that c and runtime libraries must manually be linked in. This has generally been handled by using CMake's link libraries handling but the issue with that is both de-duplication but also library link order. Standard libraries must be linked at last location to ensure symbols are always available, however this is not optimal with target_link_libraries() because this would ultimately require every library to know the c library to link with, which is not desired. Therefore, setup standard C and runtime library linking in linker CMake files for toolchains where this is required. This commit expands the principle introduced with toolchain abstraction, see PR#24851. This means that a toolchain implementation may specify standard C, runtime, C++, etc libraries, as well as their link order. Because a property approach is used, then Zephyr modules, such as the Picolibc module can adjust such properties. An optional `zephyr_linker_finalize()` macro is called at the end of Zephyr's CMakeList process and can be used by the toolchain implementation to define the final linker invocation. This aligns the linker handling flow to the principle introduced in PR#24851 and improves the flexibility and robustness of Zephyr build system. Signed-off-by: Torsten Rasmussen <[email protected]> (cherry picked from commit 2e3873a)
…nk libraries Extend zephyr_link_libraries to allow an optional value together with the `zephyr_link_libraries(PROPERTY <property> [<value>])`. This allow setting linker property combined with a value when linking Zephyr. The value will only be applied if the property is defined. Extend zephyr_compile_options to support the same PROPERTY flag that has been introduced for zephyr_link_libraries(). This remove the need for developers to write complex generator expressions for compiler flags and thus minimizes mistakes. The following syntax is now supported in addition to the existing syntax: `zephyr_compile_options(PROPERTY <property> [<value>])` Signed-off-by: Torsten Rasmussen <[email protected]> (cherry picked from commit 718b726)
The `check_set_linker_property()` and `set_linker_property()` takes a target argument. Make the target argument optional and use the target `linker` as default target. The function name `set_linker_property()` already implies that we are setting a property and the linker target. Remove the need to specify `TARGET linker` when using the default linker property target. Signed-off-by: Torsten Rasmussen <[email protected]> (cherry picked from commit 102b3fc)
…in properties Moving specs argument to compiler and linker properties so that the compiler and linker in use can decide how the flags are mapped / handled for the compiler and linker in use. This avoids specifying `--specs=spec.picolibc` for clang which prints a warning about an unused argument. Signed-off-by: Torsten Rasmussen <[email protected]> (cherry picked from commit 9d835fe)
… property This commit updates picolibc module to remove the need for hard-coding linking with `-lgcc`. Instead it sets the c_library linker property and thereby allows the Zephyr toolchain infrastructure to properly handle the linking of C and runtime libraries. Signed-off-by: Torsten Rasmussen <[email protected]> (cherry picked from commit b2eeef4)
Newlib or Picolibc libraries for LLVM may be compiled or installed from pre-built sources independently of LLVM itself. This means that always indicating that TOOLCHAIN_HAS_NEWLIB=OFF and TOOLCHAIN_HAS_PICOLIBC=OFF are wrong. But it could be just as wrong to always indicate suport for newlib or picolibc. Some pre-built LLVM toolchains are provided with default picolibc support, such as LLVM for Arm embedded, but can also be used with newlib be installing newlib add-on package. Unfortunately it's not possible to query LLVM regarding newlib or picolibc support. Developers have the option of `-DTOOLCHAIN_HAS_<NEWLIB|PICOLIBC>=ON`, but this is not widely known and cumbersome to do for each build. An indication of newlib or picolibc support is the presence of library specific headers, so to improve current situation we check for library specific headers, and if those are present we assume support for the library. This commit improves the current support for LLVM in Zephyr when cross-compiling, especially for users of LLVM for Arm embedded. Signed-off-by: Torsten Rasmussen <[email protected]> (cherry picked from commit 0274bcb)
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List of commits from Zephyr main improving support for LLVM.