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resolve_btfids: Fix linker flags detection

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The "|| echo -lzstd" default makes zstd an unconditional link
dependency of resolve_btfids. On systems where libzstd-dev is not
installed and pkg-config fails, the linker fails:

  ld: cannot find -lzstd: No such file or directory

libzstd is a transitive dependency of libelf, so the -lzstd flag is
strictly necessary only for static builds [1].

Remove ZSTD_LIBS variable, and instead set LIBELF_LIBS depending on
whether the build is static or not. Use $(HOSTPKG_CONFIG) as primary
source of the flags list.

Also add a default value for HOSTPKG_CONFIG in case it's not built via
the toplevel Makefile. Pass it from selftests/bpf too.

[1] https://lore.kernel.org/bpf/4ff82800-2daa-4b9f-95a9-6f512859ee70@linux.dev/

Reported-by: BPF CI Bot (Claude Opus 4.6) <bot+bpf-ci@kernel.org>
Reported-by: Vitaly Chikunov <vt@altlinux.org>
Closes: https://lore.kernel.org/bpf/aaWqMcK-2AQw5dx8@altlinux.org/
Fixes: 4021848a90 ("selftests/bpf: Pass through build flags to bpftool and resolve_btfids")
Signed-off-by: Ihor Solodrai <ihor.solodrai@linux.dev>
Reviewed-by: Paul Chaignon <paul.chaignon@gmail.com>
Link: https://lore.kernel.org/r/20260305014730.3123382-1-ihor.solodrai@linux.dev
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Ihor Solodrai 2026-03-04 17:47:30 -08:00 • committed by Alexei Starovoitov
parent 325d1ba3ca
commit b0dcdcb9ae
2 changed files with 8 additions and 2 deletions
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9
tools/bpf/resolve_btfids/Makefile
View file

@ -23,6 +23,7 @@ RM ?= rm
HOSTCC ?= gcc
HOSTLD ?= ld
HOSTAR ?= ar
HOSTPKG_CONFIG ?= pkg-config
CROSS_COMPILE =
OUTPUT ?= $(srctree)/tools/bpf/resolve_btfids/
@ -63,10 +64,14 @@ $(BPFOBJ): $(wildcard $(LIBBPF_SRC)/*.[ch] $(LIBBPF_SRC)/Makefile) | $(LIBBPF_OU
$(abspath $@) install_headers
LIBELF_FLAGS := $(shell $(HOSTPKG_CONFIG) libelf --cflags 2>/dev/null)
ifneq ($(filter -static,$(EXTRA_LDFLAGS)),)
LIBELF_LIBS := $(shell $(HOSTPKG_CONFIG) libelf --libs --static 2>/dev/null || echo -lelf -lzstd)
else
LIBELF_LIBS := $(shell $(HOSTPKG_CONFIG) libelf --libs 2>/dev/null || echo -lelf)
endif
ZLIB_LIBS := $(shell $(HOSTPKG_CONFIG) zlib --libs 2>/dev/null || echo -lz)
ZSTD_LIBS := $(shell $(HOSTPKG_CONFIG) libzstd --libs 2>/dev/null || echo -lzstd)
HOSTCFLAGS_resolve_btfids += -g \
-I$(srctree)/tools/include \
@ -76,7 +81,7 @@ HOSTCFLAGS_resolve_btfids += -g \
$(LIBELF_FLAGS) \
-Wall -Werror
LIBS = $(LIBELF_LIBS) $(ZLIB_LIBS) $(ZSTD_LIBS)
LIBS = $(LIBELF_LIBS) $(ZLIB_LIBS)
export srctree OUTPUT HOSTCFLAGS_resolve_btfids Q HOSTCC HOSTLD HOSTAR
include $(srctree)/tools/build/Makefile.include

1
tools/testing/selftests/bpf/Makefile
View file

@ -409,6 +409,7 @@ $(RESOLVE_BTFIDS): $(HOST_BPFOBJ) | $(HOST_BUILD_DIR)/resolve_btfids \
CC="$(HOSTCC)" LD="$(HOSTLD)" AR="$(HOSTAR)" \
LIBBPF_INCLUDE=$(HOST_INCLUDE_DIR) \
EXTRA_LDFLAGS='$(SAN_LDFLAGS) $(EXTRA_LDFLAGS)' \
HOSTPKG_CONFIG=$(PKG_CONFIG) \
OUTPUT=$(HOST_BUILD_DIR)/resolve_btfids/ BPFOBJ=$(HOST_BPFOBJ)
# Get Clang's default includes on this system, as opposed to those seen by