Hi Yonghong,
On Thu, Jan 30, 2025 at 10:28:11PM -0800, Yonghong Song wrote:
>
>
>
> On 1/30/25 2:33 PM, Daniel Xu wrote:
> > 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@xxxxxxxxx>
> > ---
> > 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.
So unfortunately, I think these probably need to be defined separately.
The code looks similar but the use cases are different.
Thanks,
Daniel
