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 <[email protected]>
---
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:
--
2.39.2.637.g21b0678d19-goog
On Fri, Feb 17, 2023 at 4:18 PM Florent Revest <[email protected]> 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 <[email protected]>:
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!
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