Re: [PATCH v1 4/6] perf: build: Only link libebl.a for old libdw

[Leo Yan]

On 6/6/24 18:40, Namhyung Kim wrote:

[...]

> > diff --git a/tools/build/feature/Makefile b/tools/build/feature/Makefile
> > index 6f52f892f9a3..2f4cfb7b8c14 100644
> > --- a/tools/build/feature/Makefile
> > +++ b/tools/build/feature/Makefile
> > @@ -159,7 +159,17 @@ $(OUTPUT)test-libopencsd.bin:
> >
> >   DWARFLIBS := -ldw
> >   ifeq ($(findstring -static,${LDFLAGS}),-static)
> > -DWARFLIBS += -lelf -lebl -lz -llzma -lbz2
> > +  DWARFLIBS += -lelf -lz -llzma -lbz2
> > +
> > +  LIBDW_VERSION := $(shell $(PKG_CONFIG) --modversion libdw)
> > +  LIBDW_VERSION_1 := $(word 1, $(subst ., ,$(LIBDW_VERSION)))
> > +  LIBDW_VERSION_2 := $(word 2, $(subst ., ,$(LIBDW_VERSION)))
> > +
> > +  # Elfutils merged libebl.a into libdw.a starting from version 0.177,
> > +  # Link libebl.a only if libdw is older than this version.
> > +  ifeq ($(shell test $(LIBDW_VERSION_2) -lt 177; echo $$?),0)
> > +    DWARFLIBS += -lebl
> > +  endif
> >   endif
>
> Is there a better way to collect required libraries using pkg-config?
> I guess that's what we want to with the pkg-config in the first place.
> Maybe `pkg-config --print-requires-private libdw` ?

Unfortunately, `pkg-config --print-requires-private libdw` does not work 
for the libebl.a after checked on Debian:buster.

  # pkg-config --modversion libdw
  0.176

  # pkg-config --print-requires-private libdw
  zlib
  liblzma

  # pkg-config --libs-only-l libdw
  -ldw -lelf

  # ldd /usr/lib/x86_64-linux-gnu/libdw.so
	linux-vdso.so.1 (0x00007fff733e3000)
	libelf.so.1 => /usr/lib/x86_64-linux-gnu/libelf.so.1 (0x0000702e24ec6000)
	libdl.so.2 => /lib/x86_64-linux-gnu/libdl.so.2 (0x0000702e24ec1000)
	libz.so.1 => /lib/x86_64-linux-gnu/libz.so.1 (0x0000702e24ea3000)
	liblzma.so.5 => /lib/x86_64-linux-gnu/liblzma.so.5 (0x0000702e24e7b000)
	libbz2.so.1.0 => /lib/x86_64-linux-gnu/libbz2.so.1.0 (0x0000702e24e68000)
	libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x0000702e24ca8000)
	/lib64/ld-linux-x86-64.so.2 (0x0000702e24f3e000)
	libpthread.so.0 => /lib/x86_64-linux-gnu/libpthread.so.0 
(0x0000702e24c85000)


I think libdw.pc cannot reflect the required dependencies, we still need 
to use a way liked in this patch (it is a bit ugly :) to link '-lebl'.

Thanks,
Leo