linux-kernel - [RFC PATCH v1 2/5] unwind_user/sframe: Add support for signal frame indication

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Message-ID: <20260127153331.2902504-3-jremus@linux.ibm.com>
Date: Tue, 27 Jan 2026 16:33:28 +0100
From: Jens Remus <jremus@...ux.ibm.com>
To: linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
        linux-s390@...r.kernel.org, bpf@...r.kernel.org, x86@...nel.org,
        Steven Rostedt <rostedt@...nel.org>
Cc: Jens Remus <jremus@...ux.ibm.com>, Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Ilya Leoshkevich <iii@...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>
Subject: [RFC PATCH v1 2/5] unwind_user/sframe: Add support for signal frame indication

SFrame V3 represents the assembler directive .cfi_signal_frame using
a SFrame FDE flag.  Note that a SFrame FDE with this particular flag set
may have no SFrame FREs.

Introduce a SFRAME_V3_FDE_SIGNAL_P() helper macro.  Use it in
__find_fre() to populate the signal flag in struct unwind_user_frame,
even if there are no FREs.

Signed-off-by: Jens Remus <jremus@...ux.ibm.com>
---
 kernel/unwind/sframe.c | 8 +++++++-
 kernel/unwind/sframe.h | 1 +
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/kernel/unwind/sframe.c b/kernel/unwind/sframe.c
index 21283e3bda42..9fd2fc1572cc 100644
--- a/kernel/unwind/sframe.c
+++ b/kernel/unwind/sframe.c
@@ -446,6 +446,7 @@ static __always_inline int __find_fre(struct sframe_section *sec,
 				      struct unwind_user_frame *frame)
 {
 	unsigned char fde_pctype = SFRAME_V3_FDE_PCTYPE(fde->info);
+	bool signal = SFRAME_V3_FDE_SIGNAL_P(fde->info);
 	struct sframe_fre_internal *fre, *prev_fre = NULL;
 	struct sframe_fre_internal fres[2];
 	unsigned long fre_addr;
@@ -486,8 +487,11 @@ static __always_inline int __find_fre(struct sframe_section *sec,
 		prev_fre = fre;
 	}
 
-	if (!prev_fre)
+	if (!prev_fre) {
+		if (signal)
+			goto signal;
 		return -EINVAL;
+	}
 	fre = prev_fre;
 
 	ret = __read_fre_datawords(sec, fde, fre);
@@ -500,6 +504,8 @@ static __always_inline int __find_fre(struct sframe_section *sec,
 	sframe_init_rule_data(&frame->fp, fre->fp_ctl, fre->fp_off);
 	frame->sp_off  = SFRAME_SP_OFFSET;
 	frame->outermost = SFRAME_V3_FRE_RA_UNDEFINED_P(fre->info);
+signal:
+	frame->signal = signal;
 
 	return 0;
 }
diff --git a/kernel/unwind/sframe.h b/kernel/unwind/sframe.h
index 8a5322e95403..78432857f84c 100644
--- a/kernel/unwind/sframe.h
+++ b/kernel/unwind/sframe.h
@@ -65,6 +65,7 @@ struct sframe_fda_v3 {
 #define SFRAME_V3_FDE_FRE_TYPE(info)		((info) & 0xf)
 #define SFRAME_V3_FDE_PCTYPE(info)		(((info) >> 4) & 0x1)
 #define SFRAME_V3_AARCH64_FDE_PAUTH_KEY(info)	(((info) >> 5) & 0x1)
+#define SFRAME_V3_FDE_SIGNAL_P(info)		(((info) >> 7) & 0x1)
 
 #define SFRAME_FDE_TYPE_REGULAR			0
 #define SFRAME_FDE_TYPE_FLEXIBLE		1
-- 
2.51.0