[PATCH 5.17 125/158] perf build: Fix check for btf__load_from_kernel_by_id() in libbpf

Greg Kroah-Hartman
2022-05-23T18:08:56Z

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-3de5-20c5-22c4-70aff4af959f@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>
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 ae61f464043a..c6a48d0ef9ff 100644
--- a/tools/build/Makefile.feature
+++ b/tools/build/Makefile.feature
@@ -98,6 +98,7 @@ 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 de66e1cc0734..cb4a2a4fa2e4 100644
--- a/tools/build/feature/Makefile
+++ b/tools/build/feature/Makefile
@@ -57,6 +57,7 @@ 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 \
@@ -287,6 +288,9 @@ $(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 f3bf9297bcc0..1bd64e7404b9 100644
--- a/tools/perf/Makefile.config
+++ b/tools/perf/Makefile.config
@@ -553,9 +553,16 @@ 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 a517eaa51eb3..65dfd2c70246 100644
--- a/tools/perf/util/bpf-event.c
+++ b/tools/perf/util/bpf-event.c
@@ -22,7 +22,8 @@
#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
@@ -32,6 +33,7 @@ struct btf * __weak btf__load_from_kernel_by_id(__u32 id)

return err ? ERR_PTR(err) : btf;
}
+#endif

struct bpf_program * __weak
bpf_object__next_program(const struct bpf_object *obj, struct bpf_program *prev)
--
2.35.1