bcc uses libbpf repo as a submodule. It brings in libbpf source
code and builds everything together to produce shared libraries.
With latest libbpf, I got the following errors:
/bin/ld: libbcc_bpf.so.0.10.0: version node not found for symbol xsk_umem__create@LIBBPF_0.0.2
/bin/ld: failed to set dynamic section sizes: Bad value
collect2: error: ld returned 1 exit status
make[2]: *** [src/cc/libbcc_bpf.so.0.10.0] Error 1
In xsk.c, we have
asm(".symver xsk_umem__create_v0_0_2, xsk_umem__create@LIBBPF_0.0.2");
asm(".symver xsk_umem__create_v0_0_4, xsk_umem__create@@LIBBPF_0.0.4");
The linker thinks the built is for LIBBPF but cannot find proper version
LIBBPF_0.0.2/4, so emit errors.
I also confirmed that using libbpf.a to produce a shared library also
has issues:
-bash-4.4$ cat t.c
extern void *xsk_umem__create;
void * test() { return xsk_umem__create; }
-bash-4.4$ gcc -c -fPIC t.c
-bash-4.4$ gcc -shared t.o libbpf.a -o t.so
/bin/ld: t.so: version node not found for symbol xsk_umem__create@LIBBPF_0.0.2
/bin/ld: failed to set dynamic section sizes: Bad value
collect2: error: ld returned 1 exit status
-bash-4.4$
Symbol versioning does happens in commonly used libraries, e.g., elfutils
and glibc. For static libraries, for a versioned symbol, the old definitions
will be ignored, and the symbol will be an alias to the latest definition.
For example, glibc sched_setaffinity is versioned.
-bash-4.4$ readelf -s /usr/lib64/libc.so.6 | grep sched_setaffinity
756: 000000000013d3d0 13 FUNC GLOBAL DEFAULT 13 sched_setaffinity@GLIBC_2.3.3
757: 00000000000e2e70 455 FUNC GLOBAL DEFAULT 13 sched_setaffinity@@GLIBC_2.3.4
1800: 0000000000000000 0 FILE LOCAL DEFAULT ABS sched_setaffinity.c
4228: 00000000000e2e70 455 FUNC LOCAL DEFAULT 13 __sched_setaffinity_new
4648: 000000000013d3d0 13 FUNC LOCAL DEFAULT 13 __sched_setaffinity_old
7338: 000000000013d3d0 13 FUNC GLOBAL DEFAULT 13 sched_setaffinity@GLIBC_2
7380: 00000000000e2e70 455 FUNC GLOBAL DEFAULT 13 sched_setaffinity@@GLIBC_
-bash-4.4$
For static library, the definition of sched_setaffinity aliases to the new definition.
-bash-4.4$ readelf -s /usr/lib64/libc.a | grep sched_setaffinity
File: /usr/lib64/libc.a(sched_setaffinity.o)
8: 0000000000000000 455 FUNC GLOBAL DEFAULT 1 __sched_setaffinity_new
12: 0000000000000000 455 FUNC WEAK DEFAULT 1 sched_setaffinity
For both elfutils and glibc, additional macros are used to control different handling
of symbol versioning w.r.t static and shared libraries.
For elfutils, the macro is SYMBOL_VERSIONING
(https://sourceware.org/git/?p=elfutils.git;a=blob;f=lib/eu-config.h).
For glibc, the macro is SHARED
(https://sourceware.org/git/?p=glibc.git;a=blob;f=include/shlib-compat.h;hb=refs/heads/master)
This patch used SYMBOL_VERSIONING as the macro name as it clearly indicates the
intention. The macro name can be changed later if necessary as it is internal
to libbpf. After this patch, the libbpf.a has
-bash-4.4$ readelf -s libbpf.a | grep xsk_umem__create
372: 0000000000017145 1190 FUNC GLOBAL DEFAULT 1 xsk_umem__create_v0_0_4
405: 0000000000017145 1190 FUNC WEAK DEFAULT 1 xsk_umem__create
499: 00000000000175eb 103 FUNC GLOBAL DEFAULT 1 xsk_umem__create_v0_0_2
-bash-4.4$
No versioned symbols for xsk_umem__create.
The libbpf.a can be used to build a shared library succesfully.
-bash-4.4$ cat t.c
extern void *xsk_umem__create;
void * test() { return xsk_umem__create; }
-bash-4.4$ gcc -c -fPIC t.c
-bash-4.4$ gcc -shared t.o libbpf.a -o t.so
-bash-4.4$
Fixes: 10d30e301732 ("libbpf: add flags to umem config")
Cc: Kevin Laatz <kevin.laatz@xxxxxxxxx>
Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Cc: Andrii Nakryiko <andriin@xxxxxx>
Signed-off-by: Yonghong Song <yhs@xxxxxx>
---
tools/lib/bpf/Makefile | 27 ++++++++++++++++++---------
tools/lib/bpf/libbpf_internal.h | 16 ++++++++++++++++
tools/lib/bpf/xsk.c | 4 ++--
3 files changed, 36 insertions(+), 11 deletions(-)
diff --git a/tools/lib/bpf/Makefile b/tools/lib/bpf/Makefile
index c6f94cffe06e..9533e185d9b6 100644
--- a/tools/lib/bpf/Makefile
+++ b/tools/lib/bpf/Makefile
@@ -110,6 +110,9 @@ override CFLAGS += $(INCLUDES)
override CFLAGS += -fvisibility=hidden
override CFLAGS += -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64
+# flags specific for shared library
+SHLIB_FLAGS = -DSYMBOL_VERSIONING
+
ifeq ($(VERBOSE),1)
Q =
else
@@ -126,14 +129,17 @@ all:
export srctree OUTPUT CC LD CFLAGS V
include $(srctree)/tools/build/Makefile.include
-BPF_IN := $(OUTPUT)libbpf-in.o
+SHARED_OBJDIR := $(OUTPUT)sharedobjs/
+STATIC_OBJDIR := $(OUTPUT)staticobjs/
+BPF_IN_SHARED := $(SHARED_OBJDIR)libbpf-in.o
+BPF_IN_STATIC := $(STATIC_OBJDIR)libbpf-in.o
VERSION_SCRIPT := libbpf.map
LIB_TARGET := $(addprefix $(OUTPUT),$(LIB_TARGET))
LIB_FILE := $(addprefix $(OUTPUT),$(LIB_FILE))
PC_FILE := $(addprefix $(OUTPUT),$(PC_FILE))
-GLOBAL_SYM_COUNT = $(shell readelf -s --wide $(BPF_IN) | \
+GLOBAL_SYM_COUNT = $(shell readelf -s --wide $(BPF_IN_SHARED) | \
cut -d "@" -f1 | sed 's/_v[0-9]_[0-9]_[0-9].*//' | \
awk '/GLOBAL/ && /DEFAULT/ && !/UND/ {print $$8}' | \
sort -u | wc -l)
@@ -155,7 +161,7 @@ all: fixdep
all_cmd: $(CMD_TARGETS) check
-$(BPF_IN): force elfdep bpfdep
+$(BPF_IN_SHARED): force elfdep bpfdep
@(test -f ../../include/uapi/linux/bpf.h -a -f ../../../include/uapi/linux/bpf.h && ( \
(diff -B ../../include/uapi/linux/bpf.h ../../../include/uapi/linux/bpf.h >/dev/null) || \
echo "Warning: Kernel ABI header at 'tools/include/uapi/linux/bpf.h' differs from latest version at 'include/uapi/linux/bpf.h'" >&2 )) || true
@@ -171,17 +177,20 @@ $(BPF_IN): force elfdep bpfdep
@(test -f ../../include/uapi/linux/if_xdp.h -a -f ../../../include/uapi/linux/if_xdp.h && ( \
(diff -B ../../include/uapi/linux/if_xdp.h ../../../include/uapi/linux/if_xdp.h >/dev/null) || \
echo "Warning: Kernel ABI header at 'tools/include/uapi/linux/if_xdp.h' differs from latest version at 'include/uapi/linux/if_xdp.h'" >&2 )) || true
- $(Q)$(MAKE) $(build)=libbpf
+ $(Q)$(MAKE) $(build)=libbpf OUTPUT=$(SHARED_OBJDIR) CFLAGS="$(CFLAGS) $(SHLIB_FLAGS)"
+
+$(BPF_IN_STATIC): force elfdep bpfdep
+ $(Q)$(MAKE) $(build)=libbpf OUTPUT=$(STATIC_OBJDIR)
$(OUTPUT)libbpf.so: $(OUTPUT)libbpf.so.$(LIBBPF_VERSION)
-$(OUTPUT)libbpf.so.$(LIBBPF_VERSION): $(BPF_IN)
+$(OUTPUT)libbpf.so.$(LIBBPF_VERSION): $(BPF_IN_SHARED)
$(QUIET_LINK)$(CC) --shared -Wl,-soname,libbpf.so.$(LIBBPF_MAJOR_VERSION) \
-Wl,--version-script=$(VERSION_SCRIPT) $^ -lelf -o $@
@ln -sf $(@F) $(OUTPUT)libbpf.so
@ln -sf $(@F) $(OUTPUT)libbpf.so.$(LIBBPF_MAJOR_VERSION)
-$(OUTPUT)libbpf.a: $(BPF_IN)
+$(OUTPUT)libbpf.a: $(BPF_IN_STATIC)
$(QUIET_LINK)$(RM) $@; $(AR) rcs $@ $^
$(OUTPUT)test_libbpf: test_libbpf.cpp $(OUTPUT)libbpf.a
@@ -197,7 +206,7 @@ check: check_abi
check_abi: $(OUTPUT)libbpf.so
@if [ "$(GLOBAL_SYM_COUNT)" != "$(VERSIONED_SYM_COUNT)" ]; then \
- echo "Warning: Num of global symbols in $(BPF_IN)" \
+ echo "Warning: Num of global symbols in $(BPF_IN_SHARED)" \
"($(GLOBAL_SYM_COUNT)) does NOT match with num of" \
"versioned symbols in $^ ($(VERSIONED_SYM_COUNT))." \
"Please make sure all LIBBPF_API symbols are" \
@@ -255,9 +264,9 @@ config-clean:
$(Q)$(MAKE) -C $(srctree)/tools/build/feature/ clean >/dev/null
clean:
- $(call QUIET_CLEAN, libbpf) $(RM) $(TARGETS) $(CXX_TEST_TARGET) \
+ $(call QUIET_CLEAN, libbpf) $(RM) -rf $(TARGETS) $(CXX_TEST_TARGET) \
*.o *~ *.a *.so *.so.$(LIBBPF_MAJOR_VERSION) .*.d .*.cmd \
- *.pc LIBBPF-CFLAGS
+ *.pc LIBBPF-CFLAGS $(SHARED_OBJDIR) $(STATIC_OBJDIR)
$(call QUIET_CLEAN, core-gen) $(RM) $(OUTPUT)FEATURE-DUMP.libbpf
diff --git a/tools/lib/bpf/libbpf_internal.h b/tools/lib/bpf/libbpf_internal.h
index 2e83a34f8c79..40a6d376de9a 100644
--- a/tools/lib/bpf/libbpf_internal.h
+++ b/tools/lib/bpf/libbpf_internal.h
@@ -34,6 +34,22 @@
(offsetof(TYPE, FIELD) + sizeof(((TYPE *)0)->FIELD))
#endif
+/* Symbol versoining is different between static and shared library.
+ * Properly versioned symbols are needed for shared library, but
+ * only the symbol of the new version is needed.
+ */
+#ifdef SYMBOL_VERSIONING
+# define OLD_VERSION(internal_name, api_name, version) \
+ asm(".symver " #internal_name "," #api_name "@" #version);
+# define NEW_VERSION(internal_name, api_name, version) \
+ asm(".symver " #internal_name "," #api_name "@@" #version);
+#else
+# define OLD_VERSION(internal_name, api_name, version)
+# define NEW_VERSION(internal_name, api_name, version) \
+ extern typeof(internal_name) api_name \
+ __attribute__ ((weak, alias (#internal_name)));
+#endif
+
extern void libbpf_print(enum libbpf_print_level level,
const char *format, ...)
__attribute__((format(printf, 2, 3)));
diff --git a/tools/lib/bpf/xsk.c b/tools/lib/bpf/xsk.c
index 24fa313524fb..6b983a4b7664 100644
--- a/tools/lib/bpf/xsk.c
+++ b/tools/lib/bpf/xsk.c
@@ -261,8 +261,8 @@ int xsk_umem__create_v0_0_2(struct xsk_umem **umem_ptr, void *umem_area,
return xsk_umem__create_v0_0_4(umem_ptr, umem_area, size, fill, comp,
&config);
}
-asm(".symver xsk_umem__create_v0_0_2, xsk_umem__create@LIBBPF_0.0.2");
-asm(".symver xsk_umem__create_v0_0_4, xsk_umem__create@@LIBBPF_0.0.4");
+OLD_VERSION(xsk_umem__create_v0_0_2, xsk_umem__create, LIBBPF_0.0.2)
+NEW_VERSION(xsk_umem__create_v0_0_4, xsk_umem__create, LIBBPF_0.0.4)
static int xsk_load_xdp_prog(struct xsk_socket *xsk)
{
--
2.17.1
