> libbpf: Detect uprobe syscall with new error
>
> In the previous optimized uprobe fix we changed the syscall
> error used for its detection from ENXIO to EPROTO.
>
> Changing related probe_uprobe_syscall detection check.
>
> Suggested-by: Andrii Nakryiko <[email protected]>
> Fixes: 05738da0efa1 ("libbpf: Add uprobe syscall feature detection")
> Signed-off-by: Jiri Olsa <[email protected]>
The Fixes: tag points to commit 05738da0efa1 ("libbpf: Add uprobe
syscall feature detection"), but wasn't the bug actually introduced by
commit 5c3c59c7952a ("uprobes/x86: Move optimized uprobe from nop5 to
nop10")? Commit 05738da0efa1 originally added the ENXIO check
correctly, but commit 5c3c59c7952a changed the kernel to return EPROTO
instead of ENXIO, breaking the libbpf detection. The commit message
even says "In the previous optimized uprobe fix we changed the syscall
error," which refers to 5c3c59c7952a.
Should this use:
Fixes: 5c3c59c7952a ("uprobes/x86: Move optimized uprobe from nop5 to nop10")
> diff --git a/tools/lib/bpf/features.c b/tools/lib/bpf/features.c
> index b7e388f99d0b..e5641fa60163 100644
> --- a/tools/lib/bpf/features.c
> +++ b/tools/lib/bpf/features.c
> @@ -577,10 +577,10 @@ static int probe_ldimm64_full_range_off(int token_fd)
> static int probe_uprobe_syscall(int token_fd)
> {
> /*
> - * If kernel supports uprobe() syscall, it will return -ENXIO when
> called
> + * If kernel supports uprobe() syscall, it will return -EPROTO when
> called
> * from the outside of a kernel-generated uprobe trampoline.
> */
> - return syscall(__NR_uprobe) < 0 && errno == ENXIO;
> + return syscall(__NR_uprobe) < 0 && errno == EPROTO;
> }
> #else
> static int probe_uprobe_syscall(int token_fd)
> diff --git a/tools/testing/selftests/bpf/prog_tests/uprobe_syscall.c
> b/tools/testing/selftests/bpf/prog_tests/uprobe_syscall.c
> index 955a37751b52..c944136252c6 100644
> --- a/tools/testing/selftests/bpf/prog_tests/uprobe_syscall.c
> +++ b/tools/testing/selftests/bpf/prog_tests/uprobe_syscall.c
> @@ -762,7 +762,7 @@ static void test_uprobe_error(void)
> long err = syscall(__NR_uprobe);
>
> ASSERT_EQ(err, -1, "error");
> - ASSERT_EQ(errno, ENXIO, "errno");
> + ASSERT_EQ(errno, EPROTO, "errno");
> }
>
> static void __test_uprobe_syscall(void)
---
AI reviewed your patch. Please fix the bug or email reply why it's not a bug.
See: https://github.com/kernel-patches/vmtest/blob/master/ci/claude/README.md
CI run summary: https://github.com/kernel-patches/bpf/actions/runs/26030080109
