linux-kernel - Re: [PATCH v11 08/15] unwind_user/sframe: Wire up unwind

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Message-ID: <20251024134415.GD3245006@noisy.programming.kicks-ass.net>
Date: Fri, 24 Oct 2025 15:44:15 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Jens Remus <jremus@...ux.ibm.com>
Cc: linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
	bpf@...r.kernel.org, x86@...nel.org, linux-mm@...ck.org,
	Steven Rostedt <rostedt@...nel.org>,
	Josh Poimboeuf <jpoimboe@...nel.org>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Ingo Molnar <mingo@...nel.org>, Jiri Olsa <jolsa@...nel.org>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Namhyung Kim <namhyung@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrii Nakryiko <andrii@...nel.org>,
	Indu Bhagat <indu.bhagat@...cle.com>,
	"Jose E. Marchesi" <jemarch@....org>,
	Beau Belgrave <beaub@...ux.microsoft.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Florian Weimer <fweimer@...hat.com>, Kees Cook <kees@...nel.org>,
	Carlos O'Donell <codonell@...hat.com>, Sam James <sam@...too.org>,
	Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	David Hildenbrand <david@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	"Liam R. Howlett" <Liam.Howlett@...cle.com>,
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
	Michal Hocko <mhocko@...e.com>, Mike Rapoport <rppt@...nel.org>,
	Suren Baghdasaryan <surenb@...gle.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	Heiko Carstens <hca@...ux.ibm.com>,
	Vasily Gorbik <gor@...ux.ibm.com>,
	"Steven Rostedt (Google)" <rostedt@...dmis.org>
Subject: Re: [PATCH v11 08/15] unwind_user/sframe: Wire up unwind_user to
 sframe

On Wed, Oct 22, 2025 at 04:43:19PM +0200, Jens Remus wrote:

> @@ -26,12 +27,10 @@ get_user_word(unsigned long *word, unsigned long base, int off, unsigned int ws)
>  	return get_user(*word, addr);
>  }
>  
> -static int unwind_user_next_fp(struct unwind_user_state *state)
> +static int unwind_user_next_common(struct unwind_user_state *state,
> +				   const struct unwind_user_frame *frame,
> +				   struct pt_regs *regs)
>  {

What is pt_regs for? AFAICT it isn't actually used in any of the
following patches.

> -	const struct unwind_user_frame fp_frame = {
> -		ARCH_INIT_USER_FP_FRAME(state->ws)
> -	};
> -	const struct unwind_user_frame *frame = &fp_frame;
>  	unsigned long cfa, fp, ra;
>  
>  	if (frame->use_fp) {
> @@ -67,6 +66,26 @@ static int unwind_user_next_fp(struct unwind_user_state *state)
>  	return 0;
>  }
>  
> +static int unwind_user_next_sframe(struct unwind_user_state *state)
> +{
> +	struct unwind_user_frame _frame, *frame;
> +
> +	/* sframe expects the frame to be local storage */
> +	frame = &_frame;
> +	if (sframe_find(state->ip, frame))
> +		return -ENOENT;
> +	return unwind_user_next_common(state, frame, task_pt_regs(current));
> +}

Would it not be simpler to write:

static int unwind_user_next_sframe(struct unwind_user_state *state)
{
	struct unwind_user_frame frame;

	/* sframe expects the frame to be local storage */
	if (sframe_find(state->ip, &frame))
		return -ENOENT;
	return unwind_user_next_common(state, &frame, task_pt_regs(current));
}

hmm?

> +static int unwind_user_next_fp(struct unwind_user_state *state)
> +{
> +	const struct unwind_user_frame fp_frame = {
> +		ARCH_INIT_USER_FP_FRAME(state->ws)
> +	};
> +
> +	return unwind_user_next_common(state, &fp_frame, task_pt_regs(current));
> +}
> +
>  static int unwind_user_next(struct unwind_user_state *state)
>  {
>  	unsigned long iter_mask = state->available_types;
> @@ -80,6 +99,16 @@ static int unwind_user_next(struct unwind_user_state *state)
>  
>  		state->current_type = type;
>  		switch (type) {
> +		case UNWIND_USER_TYPE_SFRAME:
> +			switch (unwind_user_next_sframe(state)) {
> +			case 0:
> +				return 0;
> +			case -ENOENT:
> +				continue;	/* Try next method. */
> +			default:
> +				state->done = true;
> +			}
> +			break;

Should it remove SFRAME from state->available_types at this point?