Commit
This commit does not belong to any branch on this repository, and may belong to a fork outside of the repository.
perf build: Fix check for btf__load_from_kernel_by_id() in libbpf
[ Upstream commit 0ae065a ] 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: 218e7b7 ("perf bpf: Provide a weak btf__load_from_kernel_by_id() for older libbpf versions") Reported-by: Avi Kivity <[email protected]> Link: https://lore.kernel.org/linux-perf-users/[email protected] Cc: Adrian Hunter <[email protected]> Cc: Ian Rogers <[email protected]> Cc: Jiri Olsa <[email protected]> Cc: Namhyung Kim <[email protected]> Link: https://lore.kernel.org/linux-perf-users/[email protected] Signed-off-by: Arnaldo Carvalho de Melo <[email protected]> Signed-off-by: Sasha Levin <[email protected]>
- Loading branch information