Re: [PATCH bpf-next] libbpf: fix internal USDT address translation logic for shared libraries

Jakub Sitnicki
2022-07-20T15:41:06Z

Hi Andrii,

On Wed, Jun 15, 2022 at 10:55 PM -07, Andrii Nakryiko wrote:

[...]

> This patch also changes selftests/bpf Makefile to force urand_read and
> liburand_read.so to be built with Clang and LLVM's lld (and explicitly
> request this ELF file size optimization through -znoseparate-code linker
> parameter) to validate libbpf logic and ensure regressions don't happen
> in the future. I've bundled these selftests changes together with libbpf
> changes to keep the above description tied with both libbpf and
> selftests changes.
>
> Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
> ---

[...]

> diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
> index 8ad7a733a505..e08e8e34e793 100644
> --- a/tools/testing/selftests/bpf/Makefile
> +++ b/tools/testing/selftests/bpf/Makefile
> @@ -172,13 +172,15 @@ $(OUTPUT)/%:%.c
> # do not fail. Static builds leave urandom_read relying on system-wide shared libraries.
> $(OUTPUT)/liburandom_read.so: urandom_read_lib1.c urandom_read_lib2.c
> $(call msg,LIB,,$@)
> - $(Q)$(CC) $(filter-out -static,$(CFLAGS) $(LDFLAGS)) $^ $(LDLIBS) -fPIC -shared -o $@
> + $(Q)$(CLANG) $(filter-out -static,$(CFLAGS) $(LDFLAGS)) $^ $(LDLIBS) \
> + -fuse-ld=lld -Wl,-znoseparate-code -fPIC -shared -o $@
>
> $(OUTPUT)/urandom_read: urandom_read.c urandom_read_aux.c $(OUTPUT)/liburandom_read.so
> $(call msg,BINARY,,$@)
> - $(Q)$(CC) $(filter-out -static,$(CFLAGS) $(LDFLAGS)) $(filter %.c,$^) \
> - liburandom_read.so $(LDLIBS) \
> - -Wl,-rpath=. -Wl,--build-id=sha1 -o $@
> + $(Q)$(CLANG) $(filter-out -static,$(CFLAGS) $(LDFLAGS)) $(filter %.c,$^) \
> + liburandom_read.so $(LDLIBS) \
> + -fuse-ld=lld -Wl,-znoseparate-code \
> + -Wl,-rpath=. -Wl,--build-id=sha1 -o $@

[...]

Not sure if this was considered - adding a dependency on Clang for the
target platform makes cross-compiling bpf selftests much harder than it
was.

Maybe we could use $(CLANG) only when not cross-compiling, and execute
$(CC) like before otherwise?