> commit adef46acd6e910a58509f054ca1d94c79b4c2bf2
> Author: Jiri Olsa <[email protected]>
> Date: Thu May 21 14:44:05 2026 +0200
>
> 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.
>
> Acked-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
40b54d7e3dab ("uprobes/x86: Move optimized uprobe from nop5 to nop10")?
Commit 05738da0efa1 originally added the ENXIO check correctly, but commit
40b54d7e3dab 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 40b54d7e3dab.
Should this use:
Fixes: 40b54d7e3dab ("uprobes/x86: Move optimized uprobe from nop5 to nop10")
This concern was previously raised in review by [email protected] on
Mon, 18 May 2026 11:37:54 +0000:
https://lore.kernel.org/bpf/545ca16cc113f00a390baf1ffcafba33233af771fc7c879e3c850bb33949d...@mail.kernel.org/
> 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)
[ ... ]
---
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CI run summary: https://github.com/kernel-patches/bpf/actions/runs/26227520868
