From: Arnaldo Carvalho de Melo acme@redhat.com
[ Upstream commit 0ae065a5d265bc5ada13e350015458e0c5e5c351 ]
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-3de5-20c5-22c4-70aff4af959... 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 Signed-off-by: Sasha Levin sashal@kernel.org --- tools/build/Makefile.feature | 1 + tools/build/feature/Makefile | 4 ++++ .../feature/test-libbpf-btf__load_from_kernel_by_id.c | 7 +++++++ tools/perf/Makefile.config | 7 +++++++ tools/perf/util/bpf-event.c | 4 +++- 5 files changed, 22 insertions(+), 1 deletion(-) create mode 100644 tools/build/feature/test-libbpf-btf__load_from_kernel_by_id.c
diff --git a/tools/build/Makefile.feature b/tools/build/Makefile.feature index 88dd7db55d38..6abde487bba1 100644 --- a/tools/build/Makefile.feature +++ b/tools/build/Makefile.feature @@ -97,6 +97,7 @@ FEATURE_TESTS_EXTRA := \ llvm-version \ clang \ libbpf \ + libbpf-btf__load_from_kernel_by_id \ libpfm4 \ libdebuginfod \ clang-bpf-co-re diff --git a/tools/build/feature/Makefile b/tools/build/feature/Makefile index 0e6d685b8617..69a43d9ea331 100644 --- a/tools/build/feature/Makefile +++ b/tools/build/feature/Makefile @@ -56,6 +56,7 @@ FILES= \ 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 \ @@ -283,6 +284,9 @@ $(OUTPUT)test-bpf.bin: $(OUTPUT)test-libbpf.bin: $(BUILD) -lbpf
+$(OUTPUT)test-libbpf-btf__load_from_kernel_by_id.bin: + $(BUILD) -lbpf + $(OUTPUT)test-sdt.bin: $(BUILD)
diff --git a/tools/build/feature/test-libbpf-btf__load_from_kernel_by_id.c b/tools/build/feature/test-libbpf-btf__load_from_kernel_by_id.c new file mode 100644 index 000000000000..f7c084428735 --- /dev/null +++ b/tools/build/feature/test-libbpf-btf__load_from_kernel_by_id.c @@ -0,0 +1,7 @@ +// SPDX-License-Identifier: GPL-2.0 +#include <bpf/libbpf.h> + +int main(void) +{ + return btf__load_from_kernel_by_id(20151128, NULL); +} diff --git a/tools/perf/Makefile.config b/tools/perf/Makefile.config index a92f0f025ec7..e0660bc76b7b 100644 --- a/tools/perf/Makefile.config +++ b/tools/perf/Makefile.config @@ -548,9 +548,16 @@ ifndef NO_LIBELF ifeq ($(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
diff --git a/tools/perf/util/bpf-event.c b/tools/perf/util/bpf-event.c index 16ad0e6e9e9c..cf1b9f6ec0db 100644 --- a/tools/perf/util/bpf-event.c +++ b/tools/perf/util/bpf-event.c @@ -21,7 +21,8 @@ #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 @@ -31,6 +32,7 @@ struct btf * __weak btf__load_from_kernel_by_id(__u32 id)
return err ? ERR_PTR(err) : btf; } +#endif
#define ptr_to_u64(ptr) ((__u64)(unsigned long)(ptr))