On 2/1/25 12:23 AM, Daniel Xu wrote:

Hi Yonghong,

On Thu, Jan 30, 2025 at 10:28:11PM -0800, Yonghong Song wrote:

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On 1/30/25 2:33 PM, Daniel Xu wrote:

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Since 67ab80a01886 ("selftests/bpf: Prefer static linking for LLVM libraries"), only statically linking test_progs is supported. However, some distros only provide a dynamically linkable LLVM.

This commit adds a fallback for dynamically linking LLVM if static linking is not available. If both options are available, static linking is chosen.

Signed-off-by: Daniel Xu dxu@dxuuu.xyz

tools/testing/selftests/bpf/Makefile | 11 ++++++++--- 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile index 6722080b2107..da514030a153 100644 --- a/tools/testing/selftests/bpf/Makefile +++ b/tools/testing/selftests/bpf/Makefile @@ -184,9 +184,14 @@ ifeq ($(feature-llvm),1) LLVM_CONFIG_LIB_COMPONENTS := mcdisassembler all-targets # both llvm-config and lib.mk add -D_GNU_SOURCE, which ends up as conflict LLVM_CFLAGS += $(filter-out -D_GNU_SOURCE,$(shell $(LLVM_CONFIG) --cflags))

• LLVM_LDLIBS += $(shell $(LLVM_CONFIG) --link-static --libs $(LLVM_CONFIG_LIB_COMPONENTS))
• LLVM_LDLIBS += $(shell $(LLVM_CONFIG) --link-static --system-libs $(LLVM_CONFIG_LIB_COMPONENTS))
• LLVM_LDLIBS += -lstdc++

• # Prefer linking statically if it's available, otherwise fallback to shared
• ifeq ($(shell $(LLVM_CONFIG) --link-static --libs &> /dev/null && echo static),static)
• LLVM_LDLIBS += $(shell $(LLVM_CONFIG) --link-static --libs $(LLVM_CONFIG_LIB_COMPONENTS))
• LLVM_LDLIBS += $(shell $(LLVM_CONFIG) --link-static --system-libs $(LLVM_CONFIG_LIB_COMPONENTS))
• LLVM_LDLIBS += -lstdc++
• else
• LLVM_LDLIBS += $(shell $(LLVM_CONFIG) --link-shared --libs $(LLVM_CONFIG_LIB_COMPONENTS))
• endif LLVM_LDFLAGS += $(shell $(LLVM_CONFIG) --ldflags) endif

Although your change looks good, but maybe you can look at bpftool Makefile?

# If LLVM is available, use it for JIT disassembly CFLAGS += -DHAVE_LLVM_SUPPORT LLVM_CONFIG_LIB_COMPONENTS := mcdisassembler all-targets # llvm-config always adds -D_GNU_SOURCE, however, it may already be in CFLAGS # (e.g. when bpftool build is called from selftests build as selftests # Makefile includes lib.mk which sets -D_GNU_SOURCE) which would cause # compilation error due to redefinition. Let's filter it out here. CFLAGS += $(filter-out -D_GNU_SOURCE,$(shell $(LLVM_CONFIG) --cflags)) LIBS += $(shell $(LLVM_CONFIG) --libs $(LLVM_CONFIG_LIB_COMPONENTS)) ifeq ($(shell $(LLVM_CONFIG) --shared-mode),static) LIBS += $(shell $(LLVM_CONFIG) --system-libs $(LLVM_CONFIG_LIB_COMPONENTS)) LIBS += -lstdc++ endif LDFLAGS += $(shell $(LLVM_CONFIG) --ldflags)

It would be great if the selftests shared library handling to be the same as bpftool's.

So bpftool is both an internally consumed (from selftests) dependency as well as a tool packaged up by distros. For the latter case, distros prefer dynamic linking.

I hacked llvm to have both static and shared libraries installed and indeed `llvm-config --shared-mode` prefers shared mode.

So yes, your existing change looks good. Thanks.

So unfortunately, I think these probably need to be defined separately. The code looks similar but the use cases are different.

Thanks, Daniel