[PATCH bpf-next v3] selftests/bpf: Use pkg-config to determine ld flags

[PATCH bpf-next v3] selftests/bpf: Use pkg-config to determine ld flags

[Akihiko Odaki]

When linking statically, libraries may require other dependencies to be
included to ld flags. In particular, libelf may require libzstd. Use
pkg-config to determine such dependencies.

Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
---
V2 -> V3: Added missing "echo".
V1 -> V2: Implemented fallback, referring to HOSTPKG_CONFIG.

 tools/testing/selftests/bpf/Makefile   | 4 +++-
 tools/testing/selftests/bpf/README.rst | 2 +-
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
index caede9b574cb..0b4ce6266bfc 100644
--- a/tools/testing/selftests/bpf/Makefile
+++ b/tools/testing/selftests/bpf/Makefile
@@ -4,6 +4,7 @@ include ../../../scripts/Makefile.arch
 include ../../../scripts/Makefile.include
 
 CXX ?= $(CROSS_COMPILE)g++
+PKG_CONFIG ?= $(CROSS_COMPILE)pkg-config
 
 CURDIR := $(abspath .)
 TOOLSDIR := $(abspath ../../..)
@@ -31,7 +32,8 @@ CFLAGS += -g -O0 -rdynamic -Wall -Werror $(GENFLAGS) $(SAN_CFLAGS)	\
 	  -I$(CURDIR) -I$(INCLUDE_DIR) -I$(GENDIR) -I$(LIBDIR)		\
 	  -I$(TOOLSINCDIR) -I$(APIDIR) -I$(OUTPUT)
 LDFLAGS += $(SAN_LDFLAGS)
-LDLIBS += -lelf -lz -lrt -lpthread
+LDLIBS += $(shell $(PKG_CONFIG) --libs libelf zlib || echo -lelf -lz)	\
+	  -lrt -lpthread
 
 ifneq ($(LLVM),)
 # Silence some warnings when compiled with clang
diff --git a/tools/testing/selftests/bpf/README.rst b/tools/testing/selftests/bpf/README.rst
index cb9b95702ac6..9af79c7a9b58 100644
--- a/tools/testing/selftests/bpf/README.rst
+++ b/tools/testing/selftests/bpf/README.rst
@@ -77,7 +77,7 @@ In case of linker errors when running selftests, try using static linking:
 
 .. code-block:: console
 
-  $ LDLIBS=-static vmtest.sh
+  $ LDLIBS=-static PKG_CONFIG='pkg-config --static' vmtest.sh
 
 .. note:: Some distros may not support static linking.
 
-- 
2.42.0

Re: [PATCH bpf-next v3] selftests/bpf: Use pkg-config to determine ld flags

[Daniel Borkmann]

On 10/16/23 2:43 PM, Akihiko Odaki wrote:
> When linking statically, libraries may require other dependencies to be
> included to ld flags. In particular, libelf may require libzstd. Use
> pkg-config to determine such dependencies.
> 
> Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
> ---
> V2 -> V3: Added missing "echo".
> V1 -> V2: Implemented fallback, referring to HOSTPKG_CONFIG.

Same issue in v3. Please don't resend your patches too quickly, but properly set up an
environment where you can test that this fallback works first :

https://github.com/kernel-patches/bpf/actions/runs/6533309175/job/17738285759

   [...]
   /bin/sh: 1: pkg-config: not found
   /bin/sh: 1: -lelf: not found
     BINARY   test_sysctl
   /usr/bin/x86_64-linux-gnu-ld: /usr/bin/x86_64-linux-gnu-ld: DWARF error: invalid or unhandled FORM value: 0x25
   /tmp/work/bpf/bpf/tools/testing/selftests/bpf/tools/build/libbpf/libbpf.a(libbpf-in.o): in function `bpf_object_open':
   libbpf.c:(.text+0x2871): undefined reference to `elf_version'
   /usr/bin/x86_64-linux-gnu-ld: /tmp/work/bpf/bpf/tools/testing/selftests/bpf/tools/build/libbpf/libbpf.a(libbpf-in.o): in function `bpf_object__elf_finish':
   libbpf.c:(.text+0x4ccf): undefined reference to `elf_end'
   /usr/bin/x86_64-linux-gnu-ld: /tmp/work/bpf/bpf/tools/testing/selftests/bpf/tools/build/libbpf/libbpf.a(libbpf-in.o): in function `elf_find_func_offset_from_archive':
   libbpf.c:(.text+0xb419): undefined reference to `elf_memory'
   /usr/bin/x86_64-linux-gnu-ld: libbpf.c:(.text+0xb447): undefined reference to `elf_errmsg'
   /usr/bin/x86_64-linux-gnu-ld: libbpf.c:(.text+0xb4e2): undefined reference to `elf_end'
   /usr/bin/x86_64-linux-gnu-ld: /tmp/work/bpf/bpf/tools/testing/selftests/bpf/tools/build/libbpf/libbpf.a(libbpf-in.o): in function `bpf_object__elf_init':
   libbpf.c:(.text+0x10b02): undefined reference to `elf_memory'
   /usr/bin/x86_64-linux-gnu-ld: libbpf.c:(.text+0x10bae): undefined reference to `elf_begin'
   /usr/bin/x86_64-linux-gnu-ld: libbpf.c:(.text+0x10bdd): undefined reference to `elf_errmsg'
   /usr/bin/x86_64-linux-gnu-ld: libbpf.c:(.text+0x10c1b): undefined reference to `elf_kind'
   /usr/bin/x86_64-linux-gnu-ld: libbpf.c:(.text+0x10c54): undefined reference to `gelf_getclass'
   /usr/bin/x86_64-linux-gnu-ld: libbpf.c:(.text+0x10c8d): undefined reference to `elf64_getehdr'
   /usr/bin/x86_64-linux-gnu-ld: libbpf.c:(.text+0x10cd1): undefined reference to `elf_errmsg'
   /usr/bin/x86_64-linux-gnu-ld: libbpf.c:(.text+0x10d0f): undefined reference to `elf_getshdrstrndx'
   /usr/bin/x86_64-linux-gnu-ld: libbpf.c:(.text+0x10d38): undefined reference to `elf_errmsg'
   /usr/bin/x86_64-linux-gnu-ld: libbpf.c:(.text+0x10d72): undefined reference to `elf_getscn'
   /usr/bin/x86_64-linux-gnu-ld: libbpf.c:(.text+0x10d7e): undefined reference to `elf_rawdata'
   /usr/bin/x86_64-linux-gnu-ld: libbpf.c:(.text+0x10da8): undefined reference to `elf_errmsg'

Re: [PATCH bpf-next v3] selftests/bpf: Use pkg-config to determine ld flags

[Akihiko Odaki]

On 2023/10/16 21:52, Daniel Borkmann wrote:
> On 10/16/23 2:43 PM, Akihiko Odaki wrote:
>> When linking statically, libraries may require other dependencies to be
>> included to ld flags. In particular, libelf may require libzstd. Use
>> pkg-config to determine such dependencies.
>>
>> Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
>> ---
>> V2 -> V3: Added missing "echo".
>> V1 -> V2: Implemented fallback, referring to HOSTPKG_CONFIG.
> 
> Same issue in v3. Please don't resend your patches too quickly, but 
> properly set up an
> environment where you can test that this fallback works first :
> 
> https://github.com/kernel-patches/bpf/actions/runs/6533309175/job/17738285759

I think you are looking at a wrong run. The run checks out:
https://github.com/kernel-patches/bpf/commit/0c184cb0b561d2fb60b2dc79c2917cd7ff8cd8a2

This is v2. I think the correct one is:
https://github.com/kernel-patches/bpf/actions/runs/6533797864

That said, I found spurious error messages with the run. I tested it by 
setting PKG_CONFIG=false, but I should have tested it with 
PKG_CONFIG=a-command-that-does-not-exist. Now I sent v4, which does no 
longer emit noisy error messages and is properly tested.