linux-kernel - Re: bpf_errno. Was: [PATCH RFC bpf-next 1/3] bpf: report probe fault to BPF stderr

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Message-ID: <CAADnVQK8Rw19Z6ib0CfK0cMHUsYBuhEv8_464knZ4qFZ6Gfv2g@mail.gmail.com>
Date: Thu, 9 Oct 2025 07:45:58 -0700
From: Alexei Starovoitov <alexei.starovoitov@...il.com>
To: Leon Hwang <hffilwlqm@...il.com>
Cc: Andrii Nakryiko <andrii@...nel.org>, Kumar Kartikeya Dwivedi <memxor@...il.com>, 
	Menglong Dong <menglong.dong@...ux.dev>, Menglong Dong <menglong8.dong@...il.com>, 
	Alexei Starovoitov <ast@...nel.org>, bpf <bpf@...r.kernel.org>, 
	LKML <linux-kernel@...r.kernel.org>, 
	linux-trace-kernel <linux-trace-kernel@...r.kernel.org>, jiang.biao@...ux.dev
Subject: Re: bpf_errno. Was: [PATCH RFC bpf-next 1/3] bpf: report probe fault
 to BPF stderr

On Thu, Oct 9, 2025 at 7:15 AM Leon Hwang <hffilwlqm@...il.com> wrote:
>
>
> The verifier can rewrite 'bpf_reg_aux()' into the following instructions:
>
> dst_reg = BPF_REG_AUX;
> BPF_REG_AUX = 0; /* clear BPF_REG_AUX */
>
> As for the architecture-specific implementation, BPF_REG_AUX can be
> mapped to an appropriate register per arch — for example, r11 on x86_64.

it's taken. There are no free registers.