Re: [PATCHv3 06/12] libbpf: Detect uprobe syscall with new error

[Jiri Olsa <olsajiri@gmail.com>]

On Thu, May 21, 2026 at 01:29:19PM +0000, sashiko-bot@kernel.org wrote:
> Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
> - [High] Missing kernel-side dependency causes selftest failure and feature detection breakage

replied in the previous post:
https://lore.kernel.org/bpf/agzJtkZuSRVK3YR_@krava/

jirka

> --
> 
> commit 2bfbf90e3446befa63868457a72590c57c20d562
> Author: Jiri Olsa <jolsa@kernel.org>
> 
> libbpf: Detect uprobe syscall with new error
> 
> This commit updates libbpf feature detection and selftests to expect
> EPROTO instead of ENXIO when the uprobe syscall is called outside a
> kernel-generated uprobe trampoline.
> 
> > diff --git a/tools/lib/bpf/features.c b/tools/lib/bpf/features.c
> > index 4f19a0d79b0cf..a37aaea5253e5 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;
> 
> [Severity: High]
> Is this patch missing a kernel-side dependency? Looking at the current kernel
> tree in arch/x86/kernel/uprobes.c, SYSCALL_DEFINE0(uprobe) still explicitly
> returns -ENXIO:
> 
> if (!in_uprobe_trampoline(regs->ip))
>         return -ENXIO;
> 
> Without the corresponding kernel patch to change this to -EPROTO, will
> this cause libbpf to incorrectly conclude that the uprobe syscall is
> unsupported, and cause the updated selftests below to fail?
> 
> >  }
> 
> [ ... ]
> 
> > diff --git a/tools/testing/selftests/bpf/prog_tests/uprobe_syscall.c b/tools/testing/selftests/bpf/prog_tests/uprobe_syscall.c
> > index 955a37751b52d..c944136252c6d 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");
> >  }
> 
> -- 
> Sashiko AI review · https://sashiko.dev/#/patchset/20260521124411.31133-7-jolsa@kernel.org?part=1