Avi Kivity reported a problem where the __weak
btf__load_from_kernel_by_id() in tools/perf/util/bpf-event.c was being
used and it called btf__get_from_id() in tools/lib/bpf/btf.c that in
turn called back to btf__load_from_kernel_by_id(), resulting in an
endless loop.
Fix this by adding a feature test to check if
btf__load_from_kernel_by_id() is available when building perf with
LIBBPF_DYNAMIC=1, and if not then provide the fallback to the old
btf__get_from_id(), that doesn't call back to btf__load_from_kernel_by_id()
since at that time it didn't exist at all.
Tested on Fedora 35 where we have libbpf-devel 0.4.0 with LIBBPF_DYNAMIC
where we don't have btf__load_from_kernel_by_id() and thus its feature
test fail, not defining HAVE_LIBBPF_BTF__LOAD_FROM_KERNEL_BY_ID:
$ cat /tmp/build/perf-urgent/feature/test-libbpf-btf__load_from_kernel_by_id.make.output
test-libbpf-btf__load_from_kernel_by_id.c: In function ‘main’:
test-libbpf-btf__load_from_kernel_by_id.c:6:16: error: implicit declaration of function ‘btf__load_from_kernel_by_id’ [-Werror=implicit-function-declaration]
6 | return btf__load_from_kernel_by_id(
20151128, NULL);
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~
cc1: all warnings being treated as errors
$
$ nm /tmp/build/perf-urgent/perf | grep btf__load_from_kernel_by_id
00000000005ba180 T btf__load_from_kernel_by_id
$
$ objdump --disassemble=btf__load_from_kernel_by_id -S /tmp/build/perf-urgent/perf
/tmp/build/perf-urgent/perf: file format elf64-x86-64
<SNIP>
00000000005ba180 <btf__load_from_kernel_by_id>:
#include "record.h"
#include "util/synthetic-events.h"
#ifndef HAVE_LIBBPF_BTF__LOAD_FROM_KERNEL_BY_ID
struct btf *btf__load_from_kernel_by_id(__u32 id)
{
5ba180: 55 push %rbp
5ba181: 48 89 e5 mov %rsp,%rbp
5ba184: 48 83 ec 10 sub $0x10,%rsp
5ba188: 64 48 8b 04 25 28 00 mov %fs:0x28,%rax
5ba18f: 00 00
5ba191: 48 89 45 f8 mov %rax,-0x8(%rbp)
5ba195: 31 c0 xor %eax,%eax
struct btf *btf;
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wdeprecated-declarations"
int err = btf__get_from_id(id, &btf);
5ba197: 48 8d 75 f0 lea -0x10(%rbp),%rsi
5ba19b: e8 a0 57 e5 ff call 40f940 <btf__get_from_id@plt>
5ba1a0: 89 c2 mov %eax,%edx
#pragma GCC diagnostic pop
return err ? ERR_PTR(err) : btf;
5ba1a2: 48 98 cltq
5ba1a4: 85 d2 test %edx,%edx
5ba1a6: 48 0f 44 45 f0 cmove -0x10(%rbp),%rax
}
<SNIP>
Fixes: 218e7b775d368f38 ("perf bpf: Provide a weak btf__load_from_kernel_by_id() for older libbpf versions")
Reported-by: Avi Kivity <avi@scylladb.com>
Link: https://lore.kernel.org/linux-perf-users/f0add43b-3de5-20c5-22c4-70aff4af959f@scylladb.com
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: https://lore.kernel.org/linux-perf-users/YobjjFOblY4Xvwo7@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
llvm-version \
clang \
libbpf \
+ libbpf-btf__load_from_kernel_by_id \
libpfm4 \
libdebuginfod \
clang-bpf-co-re
test-lzma.bin \
test-bpf.bin \
test-libbpf.bin \
+ test-libbpf-btf__load_from_kernel_by_id.bin \
test-get_cpuid.bin \
test-sdt.bin \
test-cxx.bin \
$(OUTPUT)test-libbpf.bin:
$(BUILD) -lbpf
+$(OUTPUT)test-libbpf-btf__load_from_kernel_by_id.bin:
+ $(BUILD) -lbpf
+
$(OUTPUT)test-sdt.bin:
$(BUILD)
--- /dev/null
+// SPDX-License-Identifier: GPL-2.0
+#include <bpf/libbpf.h>
+
+int main(void)
+{
+ return btf__load_from_kernel_by_id(20151128, NULL);
+}
ifeq ($(feature-libbpf), 1)
EXTLIBS += -lbpf
$(call detected,CONFIG_LIBBPF_DYNAMIC)
+
+ $(call feature_check,libbpf-btf__load_from_kernel_by_id)
+ ifeq ($(feature-libbpf-btf__load_from_kernel_by_id), 1)
+ CFLAGS += -DHAVE_LIBBPF_BTF__LOAD_FROM_KERNEL_BY_ID
+ endif
else
dummy := $(error Error: No libbpf devel library found, please install libbpf-devel);
endif
+ else
+ CFLAGS += -DHAVE_LIBBPF_BTF__LOAD_FROM_KERNEL_BY_ID
endif
endif
#include "record.h"
#include "util/synthetic-events.h"
-struct btf * __weak btf__load_from_kernel_by_id(__u32 id)
+#ifndef HAVE_LIBBPF_BTF__LOAD_FROM_KERNEL_BY_ID
+struct btf *btf__load_from_kernel_by_id(__u32 id)
{
struct btf *btf;
#pragma GCC diagnostic push
return err ? ERR_PTR(err) : btf;
}
+#endif
int __weak bpf_prog_load(enum bpf_prog_type prog_type,
const char *prog_name __maybe_unused,
projects / kernel.git / commitdiff