linux-kernel - [PATCH v12 07/13] unwind_user: Stop when reaching an outermost frame

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Message-ID: <20251119132323.1281768-8-jremus@linux.ibm.com>
Date: Wed, 19 Nov 2025 14:23:17 +0100
From: Jens Remus <jremus@...ux.ibm.com>
To: 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>
Cc: Jens Remus <jremus@...ux.ibm.com>, Josh Poimboeuf <jpoimboe@...nel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Peter Zijlstra <peterz@...radead.org>, 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>,
        Dylan Hatch <dylanbhatch@...gle.com>, 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>
Subject: [PATCH v12 07/13] unwind_user: Stop when reaching an outermost frame

Add an indication for an outermost frame to the unwind user frame
structure and stop unwinding when reaching an outermost frame.

This will be used by unwind user sframe, as SFrame may represent an
undefined return address as indication for an outermost frame.

Cc: Steven Rostedt <rostedt@...nel.org>
Cc: Josh Poimboeuf <jpoimboe@...nel.org>
Cc: Masami Hiramatsu <mhiramat@...nel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Jiri Olsa <jolsa@...nel.org>
Cc: Arnaldo Carvalho de Melo <acme@...nel.org>
Cc: Namhyung Kim <namhyung@...nel.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Andrii Nakryiko <andrii@...nel.org>
Cc: Indu Bhagat <indu.bhagat@...cle.com>
Cc: "Jose E. Marchesi" <jemarch@....org>
Cc: Beau Belgrave <beaub@...ux.microsoft.com>
Cc: Jens Remus <jremus@...ux.ibm.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Florian Weimer <fweimer@...hat.com>
Cc: Sam James <sam@...too.org>
Cc: Kees Cook <kees@...nel.org>
Cc: "Carlos O'Donell" <codonell@...hat.com>
Signed-off-by: Jens Remus <jremus@...ux.ibm.com>
---

Notes (jremus):
    Changes in v12:
    - Adjust to Peter's tip perf/core commit ae25884ad749 ("unwind_user/x86:
      Teach FP unwind about start of function").
    
    Changes in v11:
    - New patch.

 arch/x86/include/asm/unwind_user.h | 6 ++++--
 include/linux/unwind_user_types.h  | 1 +
 kernel/unwind/user.c               | 6 ++++++
 3 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/unwind_user.h b/arch/x86/include/asm/unwind_user.h
index 12064284bc4e..f9a1c460150d 100644
--- a/arch/x86/include/asm/unwind_user.h
+++ b/arch/x86/include/asm/unwind_user.h
@@ -11,13 +11,15 @@
 	.cfa_off	=  2*(ws),			\
 	.ra_off		= -1*(ws),			\
 	.fp_off		= -2*(ws),			\
-	.use_fp		= true,
+	.use_fp		= true,				\
+	.outermost	= false,
 
 #define ARCH_INIT_USER_FP_ENTRY_FRAME(ws)		\
 	.cfa_off	=  1*(ws),			\
 	.ra_off		= -1*(ws),			\
 	.fp_off		= 0,				\
-	.use_fp		= false,
+	.use_fp		= false,			\
+	.outermost	= false,
 
 static inline int unwind_user_word_size(struct pt_regs *regs)
 {
diff --git a/include/linux/unwind_user_types.h b/include/linux/unwind_user_types.h
index 43e4b160883f..616cc5ee4586 100644
--- a/include/linux/unwind_user_types.h
+++ b/include/linux/unwind_user_types.h
@@ -32,6 +32,7 @@ struct unwind_user_frame {
 	s32 ra_off;
 	s32 fp_off;
 	bool use_fp;
+	bool outermost;
 };
 
 struct unwind_user_state {
diff --git a/kernel/unwind/user.c b/kernel/unwind/user.c
index 7644ab9f6a61..d053295b1f7e 100644
--- a/kernel/unwind/user.c
+++ b/kernel/unwind/user.c
@@ -32,6 +32,12 @@ static int unwind_user_next_common(struct unwind_user_state *state,
 {
 	unsigned long cfa, fp, ra;
 
+	/* Stop unwinding when reaching an outermost frame. */
+	if (frame->outermost) {
+		state->done = true;
+		return 0;
+	}
+
 	if (frame->use_fp) {
 		if (state->fp < state->sp)
 			return -EINVAL;
-- 
2.48.1