linux-kernel - [PATCH v4 06/12] unwind_user/sframe: Enable archs with encoded SFrame CFA offsets

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Message-ID: <20260127151926.2805123-7-jremus@linux.ibm.com>
Date: Tue, 27 Jan 2026 16:19:19 +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: [PATCH v4 06/12] unwind_user/sframe: Enable archs with encoded SFrame CFA offsets

Enable architectures, such as s390, which store SFrame CFA offset values
encoded, to e.g. make (better) use of unsigned 8-bit SFrame offsets.

Signed-off-by: Jens Remus <jremus@...ux.ibm.com>
---

Notes (jremus):
    Changes in RFC v2:
    - Rename generic_sframe_cfa_offset_decode() to
      sframe_cfa_offset_decode(). (Josh)

 include/asm-generic/unwind_user_sframe.h | 8 ++++++++
 kernel/unwind/sframe.c                   | 2 ++
 2 files changed, 10 insertions(+)

diff --git a/include/asm-generic/unwind_user_sframe.h b/include/asm-generic/unwind_user_sframe.h
index 8c9ac47bc8bd..117b05e1dcab 100644
--- a/include/asm-generic/unwind_user_sframe.h
+++ b/include/asm-generic/unwind_user_sframe.h
@@ -9,4 +9,12 @@
 #define SFRAME_SP_OFFSET 0
 #endif
 
+#ifndef sframe_cfa_offset_decode
+static inline s32 sframe_cfa_offset_decode(s32 offset)
+{
+	return offset;
+}
+#define sframe_cfa_offset_decode sframe_cfa_offset_decode
+#endif
+
 #endif /* _ASM_GENERIC_UNWIND_USER_SFRAME_H */
diff --git a/kernel/unwind/sframe.c b/kernel/unwind/sframe.c
index 6a6221ce6d12..5ac502f16bad 100644
--- a/kernel/unwind/sframe.c
+++ b/kernel/unwind/sframe.c
@@ -209,6 +209,7 @@ __read_regular_fre_datawords(struct sframe_section *sec,
 
 	UNSAFE_GET_USER_INC(cfa_off, cur, dataword_size, Efault);
 	dataword_count--;
+	cfa_off = sframe_cfa_offset_decode(cfa_off);
 
 	ra_off = sec->ra_off;
 	if (!ra_off && dataword_count) {
@@ -258,6 +259,7 @@ __read_flex_fde_fre_datawords(struct sframe_section *sec,
 	UNSAFE_GET_USER_INC(cfa_ctl, cur, dataword_size, Efault);
 	UNSAFE_GET_USER_INC(cfa_off, cur, dataword_size, Efault);
 	dataword_count -= 2;
+	cfa_off = sframe_cfa_offset_decode(cfa_off);
 
 	ra_off = sec->ra_off;
 	ra_ctl = ra_off ? 2 : 0; /* regnum=0, deref_p=(ra_off != 0), reg_p=0 */
-- 
2.51.0