[libcxx] Remove clang-18 workaround in picolib build #133254
Conversation
clang-19 changed how Arm triples were normalised and so while we supported 18 and 19, we could not hard code the path here. Now that Linaro's bots are running clang-19, and libcxx is going to drop clang-18 support (llvm#130142) I have simplified it by hard coding the path again. I also looked into why this exists in the first place. It was added in https://reviews.llvm.org/D154246 but not questioned at the time. It is due to the way we build compiler-rt, which is due to the final layout we need in the install: 1. The builtins library must be called libclang_rt.builtins.a for clang to find it. There must not be an architecture name in the filename. 2. That builtins library must be directly in lib/, next to picolib's installed files. To achieve #1 we must set LLVM_ENABLE_PER_TARGET_RUNTIME_DIR=ON. However, that causes the file to be installed in a per-target dir which breaks #2. So to fix that, we move the builtins library up one level into lib/. The alternative is to turn off per-target dirs, which results in a builtin file with an arch in the name, then rename and move that file (since it gets installed into lib/generic/). So in the end, it's the same amount of hacks. I think it's best to keep the one that uses LLVM_ENABLE_PER_TARGET_RUNTIME_DIR=ON, as this is the recommended way to built these days.
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@llvm/pr-subscribers-libcxx Author: David Spickett (DavidSpickett) Changesclang-19 changed how Arm triples were normalised and so while we supported 18 and 19, we could not hard code the path here. Now that Linaro's bots are running clang-19, and libcxx is going to drop clang-18 support (#130142) I have simplified it by hard coding the path again. I also looked into why this exists in the first place. It was added in https://reviews.llvm.org/D154246 but not questioned at the time. It is due to the way we build compiler-rt, which is due to the final layout we need in the install:
To achieve #1 we must set LLVM_ENABLE_PER_TARGET_RUNTIME_DIR=ON. However, that causes the file to be installed in a per-target dir which breaks #2. So to fix that, we move the builtins library up one level into lib/. The alternative is to turn off per-target dirs, which results in a builtin file with an arch in the name, then rename and move that file (since it gets installed into lib/generic/). So in the end, it's the same amount of hacks. I think it's best to keep the one that uses LLVM_ENABLE_PER_TARGET_RUNTIME_DIR=ON, as this is the recommended way to built these days. Full diff: https://github.com/llvm/llvm-project/pull/133254.diff 1 Files Affected:
diff --git a/libcxx/utils/ci/run-buildbot b/libcxx/utils/ci/run-buildbot
index 29eebd1f92189..92f593595cef2 100755
--- a/libcxx/utils/ci/run-buildbot
+++ b/libcxx/utils/ci/run-buildbot
@@ -204,6 +204,11 @@ function test-armv7m-picolibc() {
step "Generating CMake for compiler-rt"
flags="--sysroot=${INSTALL_DIR}"
+ # LLVM_ENABLE_PER_TARGET_RUNTIME_DIR=ON means that we produce a file
+ # libclang_rt.builtins.a that will be installed to lib/armv7m-unknown-none-eabi/.
+ # With LLVM_ENABLE_PER_TARGET_RUNTIME_DIR=OFF, the filename includes the
+ # architecture name, which is not what Clang's driver expects to find.
+ # The install location will however be wrong, we correct that below.
${CMAKE} \
-S "${MONOREPO_ROOT}/compiler-rt" \
-B "${BUILD_DIR}/compiler-rt" \
@@ -226,13 +231,8 @@ function test-armv7m-picolibc() {
step "Installing compiler-rt"
${NINJA} -vC "${BUILD_DIR}/compiler-rt" install
-
- # Prior to clang 19, armv7m-none-eabi normalised to armv7m-none-unknown-eabi.
- # clang 19 changed this to armv7m-unknown-none-eabi. So for as long as 18.x
- # is supported, we have to ask clang what the triple will be.
- NORMALISED_TARGET_TRIPLE=$(${CC-cc} --target=armv7m-none-eabi -print-target-triple)
- # Without this step linking fails later in the build.
- mv "${BUILD_DIR}/install/lib/${NORMALISED_TARGET_TRIPLE}"/* "${BUILD_DIR}/install/lib"
+ # Move compiler-rt libs into the same directory as all the picolib objects.
+ mv "${BUILD_DIR}/install/lib/armv7m-unknown-none-eabi"/* "${BUILD_DIR}/install/lib"
check-runtimes
}
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@domin144 I know you are free of all this now but shout if there's anything super obviously wrong. |
clang-19 changed how Arm triples were normalised and so while we supported 18 and 19, we could not hard code the path here.
Now that Linaro's bots are running clang-19, and libcxx is going to drop clang-18 support (#130142) I have simplified it by hard coding the path again.
I also looked into why this exists in the first place. It was added in https://reviews.llvm.org/D154246 but not questioned at the time.
It is due to the way we build compiler-rt, which is due to the final layout we need in the install:
To achieve number 1 we must set LLVM_ENABLE_PER_TARGET_RUNTIME_DIR=ON. However, that causes the file to be installed in a per-target dir which breaks number 2. So to fix that, we move the builtins library up one level into lib/.
The alternative is to turn off per-target dirs, which results in a builtin file with an arch in the name, then rename and move that file (since it gets installed into lib/generic/).
So in the end, it's the same amount of hacks. I think it's best to keep the one that uses LLVM_ENABLE_PER_TARGET_RUNTIME_DIR=ON, as this is the recommended way to built these days.