I cross-compile my BPF selftests with the following command:
CLANG_CROSS_FLAGS="--target=aarch64-linux-gnu --sysroot=/sysroot/" \ make LLVM=1 CC=clang CROSS_COMPILE=aarch64-linux-gnu- SRCARCH=arm64
(Note the use of CLANG_CROSS_FLAGS to specify a custom sysroot instead of letting clang use gcc's default sysroot)
However, CLANG_CROSS_FLAGS gets propagated to host tools builds (libbpf and bpftool) and because they reference it directly in their Makefiles, they end up cross-compiling host objects which results in linking errors.
This patch ensures that CLANG_CROSS_FLAGS is reset if CROSS_COMPILE isn't set (for example when reaching a BPF host tool build).
Signed-off-by: Florent Revest revest@chromium.org --- tools/scripts/Makefile.include | 2 ++ 1 file changed, 2 insertions(+)
diff --git a/tools/scripts/Makefile.include b/tools/scripts/Makefile.include index 0efb8f2b33ce..ff527ac065cf 100644 --- a/tools/scripts/Makefile.include +++ b/tools/scripts/Makefile.include @@ -108,6 +108,8 @@ endif # GCC_TOOLCHAIN_DIR endif # CLANG_CROSS_FLAGS CFLAGS += $(CLANG_CROSS_FLAGS) AFLAGS += $(CLANG_CROSS_FLAGS) +else +CLANG_CROSS_FLAGS := endif # CROSS_COMPILE
# Hack to avoid type-punned warnings on old systems such as RHEL5:
On Fri, Feb 17, 2023 at 4:18 PM Florent Revest revest@chromium.org wrote:
I cross-compile my BPF selftests with the following command:
CLANG_CROSS_FLAGS="--target=aarch64-linux-gnu --sysroot=/sysroot/" \ make LLVM=1 CC=clang CROSS_COMPILE=aarch64-linux-gnu- SRCARCH=arm64
(Note the use of CLANG_CROSS_FLAGS to specify a custom sysroot instead of letting clang use gcc's default sysroot)
However, CLANG_CROSS_FLAGS gets propagated to host tools builds (libbpf and bpftool) and because they reference it directly in their Makefiles, they end up cross-compiling host objects which results in linking errors.
This patch ensures that CLANG_CROSS_FLAGS is reset if CROSS_COMPILE isn't set (for example when reaching a BPF host tool build).
Note: I'm not entirely sure which tree should take that patch. I tagged this patch as "bpf-next" because 1- that's the tree I know best 2- as far as I can tell, only BPF tools Makefiles reference CLANG_CROSS_FLAGS directly and are currently broken in this way 3- I figured this would be a simple enough patch that it's not too hard for another tree to take it.
Anyway, I tried to CC other relevant folks, I figured there could be different opinions on how this should get solved, for example the bpf Makefiles using CLANG_CROSS_FLAGS could check whether CROSS_COMPILE is set first. I'd be happy to adapt a v2 to any suggestion.
Hello:
This patch was applied to bpf/bpf-next.git (master) by Alexei Starovoitov ast@kernel.org:
On Fri, 17 Feb 2023 16:18:32 +0100 you wrote:
I cross-compile my BPF selftests with the following command:
CLANG_CROSS_FLAGS="--target=aarch64-linux-gnu --sysroot=/sysroot/" \ make LLVM=1 CC=clang CROSS_COMPILE=aarch64-linux-gnu- SRCARCH=arm64
(Note the use of CLANG_CROSS_FLAGS to specify a custom sysroot instead of letting clang use gcc's default sysroot)
[...]
Here is the summary with links: - [bpf-next] selftests/bpf: Fix cross compilation with CLANG_CROSS_FLAGS https://git.kernel.org/bpf/bpf-next/c/b539a287baaa
You are awesome, thank you!
linux-kselftest-mirror@lists.linaro.org
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Florent Revest -
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