[ATfE] Add CMake Build Options for Multiple C Libraries #687

HugoSilvaSantos · 2026-01-20T18:10:43Z

Draft PR

dcandler · 2026-01-22T13:43:02Z

arm-software/embedded/arm-multilib/CMakeLists.txt

 if(NOT ENABLE_VARIANTS STREQUAL "all")
    foreach(expected_variant ${ENABLE_VARIANTS})
        if(NOT expected_variant IN_LIST enabled_variants)
-            message(FATAL_ERROR "Variant name ${expected_variant} not found in ${MULTILIB_JSON}")


Improving the error messaging is probably better done in a separate PR, since this is unrelated to the llvm-libc work which is already a large enough change,

arm-software/embedded/arm-runtimes/CMakeLists.txt

arm-software/embedded/CMakeLists.txt

dcandler · 2026-01-22T13:54:59Z

arm-software/embedded/CMakeLists.txt

+# Allow callers to provide URL-encoded semicolons (\"%3B\") so that lists can
+# be passed through shell commands without extra escaping.
+string(REPLACE "%3B" ";" LLVM_TOOLCHAIN_LIBRARY_VARIANTS "${LLVM_TOOLCHAIN_LIBRARY_VARIANTS}")
+string(REPLACE "%3b" ";" LLVM_TOOLCHAIN_LIBRARY_VARIANTS "${LLVM_TOOLCHAIN_LIBRARY_VARIANTS}")


I'm not sure why this is necessary since it sounds like a problem with the shell commands rather than the CMake. I don't think it would be a good idea to go down this road if it leads to trying to make every CMake list option support multiple delimiters, instead of fixing the callers.

dcandler · 2026-01-22T13:58:48Z

arm-software/embedded/CMakeLists.txt

@@ -167,11 +171,28 @@ set(
 set(FVP_CONFIG_DIR "${CMAKE_CURRENT_SOURCE_DIR}/fvp/config")
 set(LLVM_TOOLCHAIN_C_LIBRARY
    "picolibc" CACHE STRING


If this is retained as a legacy setting, then it shouldn't have a default setting to always enable it. Though it might be easier to simply make it throw an error to tell people to stop using it.

dcandler · 2026-01-22T15:26:09Z

arm-software/embedded/CMakeLists.txt

 # If you want to stop cmake updating the repos then run
 # cmake . -DFETCHCONTENT_FULLY_DISCONNECTED=ON
-if(LLVM_TOOLCHAIN_C_LIBRARY STREQUAL picolibc)
+if("picolibc" IN_LIST LLVM_TOOLCHAIN_ENABLED_LIBCS)


Rather than check the list, LLVM_TOOLCHAIN_ENABLE_PICOLIBC should already conatin whether picolibc is used or not.

dcandler · 2026-01-22T15:31:54Z

arm-software/embedded/CMakeLists.txt

-  endif()
+    list(LENGTH LLVM_TOOLCHAIN_ENABLED_LIBCS _overlay_libc_count)
+    if(NOT _overlay_libc_count EQUAL 1)
+        message(FATAL_ERROR


I don't think these restrictions are still needed. Eventually, a picolibc overlay may be needed, and having an overlay contain multiple libcs would also be covenient to generate for the same reason as a standard toolchain package.

dcandler · 2026-01-22T15:39:39Z

arm-software/embedded/CMakeLists.txt

    include(${CMAKE_CURRENT_SOURCE_DIR}/cmake/fetch_picolibc.cmake)
 endif()
-if(LLVM_TOOLCHAIN_C_LIBRARY MATCHES "^newlib")
+if("newlib" IN_LIST LLVM_TOOLCHAIN_ENABLED_LIBCS


Likewise checking LLVM_TOOLCHAIN_ENABLE_NEWLIB (and/or the LLVM_TOOLCHAIN_ENABLE_NEWLIB_NANO suggested above)

dcandler · 2026-01-23T09:23:55Z

arm-software/embedded/CMakeLists.txt

+    if(libc MATCHES "^newlib")
+        install(
+            FILES
+            ${CMAKE_CURRENT_SOURCE_DIR}/ATfE-SBOM-newlib-overlay.spdx.json


The current SBOMs are hardcoded, so the overlay files may not be correct for non-overlay packages.

Overlay SBOM should cover the library only, today if one unpacks all overlays they would get the main SBOM + library SBOMs that are expected to be consistent. I think the same logic will apply to the combined package.
In the future, we may want to split picolibc out, when it can be an overlay.

At the moment, ATfE-SBOM.spdx.json covers both LLVM toolchain components and picolibc, so yes the picolibc parts will need splitting out since it's possible to build a package without it, but the rest of the SBOM covering the toolchain is still needed.

It may help to drop the 'overlay' part of the name, and simply add the required SBOMs based on whether each library is enabled, regardless of whether the overlay layout is used.

Agreed, ATfE-SBOM-<lib name>.spdx.json should be good, however this is a separate improvement.

dcandler · 2026-01-23T09:24:45Z

arm-software/embedded/CMakeLists.txt

+            DESTINATION
+            ${LIBC_CFG_DIR}
+        )
+    endif()


If no match is found, it would be better to throw an error so that files aren't accidentally missed later if the names change,

dcandler · 2026-01-26T09:30:03Z

arm-software/embedded/CMakeLists.txt

        set(PACKAGE_FILE_NAME ${PACKAGE_NAME}-${PACKAGE_VERSION}-${CPACK_SYSTEM_NAME})
    else()
-        set(PACKAGE_FILE_NAME ${PACKAGE_NAME}_${LLVM_TOOLCHAIN_C_LIBRARY}-${PACKAGE_VERSION}-${CPACK_SYSTEM_NAME})
+        set(PACKAGE_FILE_NAME ${PACKAGE_NAME}_${LLVM_TOOLCHAIN_PRIMARY_LIBC}-${PACKAGE_VERSION}-${CPACK_SYSTEM_NAME})


A new naming scheme is needed, otherwise a package with picolibc+llvmlibc will have the same name as a picolibc+newlib package, or one that only includes picolibc

dcandler · 2026-01-26T09:31:28Z

arm-software/embedded/CMakeLists.txt

-add_custom_target(check-${LLVM_TOOLCHAIN_C_LIBRARY})
+set(LLVM_TOOLCHAIN_LIBC_CHECK_TARGETS "")
+foreach(libc IN LISTS LLVM_TOOLCHAIN_ENABLED_LIBCS)
+    set(_libc_check_target check-${libc})


Having a single check-libc target to run all the libc tests would make more sense to a user. Then individual libc tests could be invoked through e.g. check-multilib-picolibc-libc or check-multilib-llvmlibc-libc?

Again we may want to settle on a better naming scheme since using the name of the libc as the multilib and the test target may quickly get confusing.

dcandler · 2026-01-26T11:45:26Z

arm-software/embedded/CMakeLists.txt

-        foreach(check_target check-${LLVM_TOOLCHAIN_C_LIBRARY} check-compiler-rt check-cxx check-cxxabi check-unwind)
+    foreach(libc IN LISTS LLVM_TOOLCHAIN_ENABLED_LIBCS)
+        set(multilib_project multilib-${libc})
+        set(libc_install_dir ${CMAKE_CURRENT_BINARY_DIR}/llvm/${TARGET_LIBRARIES_DIR}/${libc})


Only the libcs that are in addition to the default/primary one need to be placed in a subdirectory (unless an overlay is being generated). Likewise a configuration file won't be needed for every libc, sice the configuration file exists to select the non-default directory.

dcandler · 2026-01-26T13:19:49Z

arm-software/embedded/CMakeLists.txt

+foreach(libc IN LISTS LLVM_TOOLCHAIN_ENABLED_LIBCS)
+    if(libc STREQUAL picolibc)
+        set(_libc_display_name "Picolibc")
+        set(_libc_license_names COPYING.NEWLIB COPYING.picolibc)


COPYING.NEWLIB was removed from picolibc, so there's no reason to try in include it.

dcandler · 2026-01-26T13:24:19Z

arm-software/embedded/CMakeLists.txt

+foreach(libc IN LISTS LLVM_TOOLCHAIN_ENABLED_LIBCS)
+    if(libc STREQUAL picolibc)
+        set(libc_license_sources "")
+        set(_picolibc_newlib_license ${picolibc_SOURCE_DIR}/COPYING.NEWLIB)


As above, picolibc no longer has COPYING.NEWLIB in its sources, so the file will never be found and there's no reason to always trigger the warning.

Similarly defining the license file names above and then their paths+names again here in two separate loops seems unnecessary and it should be possible to combine them - and not rely on a string matching loop (the files needed should be determined by the CMake options)

- Add enable flags per libc

- Fix COPYING.NEWLIB error when creating the atfe package - Fix samples related issue

github-actions · 2026-01-27T16:28:57Z

This pull review modifies files outside of the arm-software directory, so please ensure it follows the Downstream Patch Policy.
An automated check will test if the tagging requirements have been met. Please wait for approving reviews from both Arm Toolchain for Embedded and Arm Toolchain for Linux teams before merging.

dcandler reviewed Jan 23, 2026

View reviewed changes

dcandler reviewed Jan 26, 2026

View reviewed changes

Hugo Silva and others added 4 commits January 27, 2026 16:09

Support multiple libc libraries in ATfE

c778064

- Add enable flags per libc

Update cmake files

6c1a55d

Update CMAKE file to fix 2 issues

c2fa22d

- Fix COPYING.NEWLIB error when creating the atfe package - Fix samples related issue

Remove .patch file

37e947a

github-actions bot added the downstream-change Downstream change to LLVM tree label Jan 27, 2026

HugoSilvaSantos force-pushed the arm-software-libc-atfe-package branch from 793356a to 37e947a Compare January 27, 2026 16:38

dcandler removed the downstream-change Downstream change to LLVM tree label Jan 27, 2026

HugoSilvaSantos added 2 commits January 28, 2026 11:04

Merge branch 'arm:arm-software' into arm-software-libc-atfe-package

04b7535

Delete code previously removed in different commits

bee19dc

[ATfE] Add CMake Build Options for Multiple C Libraries #687

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[ATfE] Add CMake Build Options for Multiple C Libraries #687

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HugoSilvaSantos commented Jan 20, 2026

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github-actions bot commented Jan 27, 2026

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