Re: [PATCHv4 07/13] libbpf: Detect uprobe syscall with new error

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] The uprobe syscall feature detection and selftest changes expect the kernel to return `-EPROTO`, but the corresponding kernel patch is missing from the tree, causing test failures and feature regression.
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commit 241886d344e64ee01c001ddedecbb173dc73fef3
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 for the uprobe syscall. The change is intended to align
with an optimized uprobe fix in the kernel.

> 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: Medium]
The commit message mentions a "previous optimized uprobe fix", but is that
patch present in the current tree?

In arch/x86/kernel/uprobes.c, sys_uprobe() still returns -ENXIO. Does this
cause probe_uprobe_syscall() to return false and silently disable the
optimized uprobes feature?

>  }
>  #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 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");

[Severity: Medium]
Will this test now deterministically fail? Since the kernel still returns
-ENXIO, it seems errno will be ENXIO instead of EPROTO.

>  }
>  
>  static void __test_uprobe_syscall(void)

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Sashiko AI review · https://sashiko.dev/#/patchset/20260526205840.173790-8-jolsa@kernel.org?part=1