linux-kernel - [PATCH 12/12] unwind_user/x86: Enable frame pointer unwinding on x86

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Message-ID: <20250924080119.736377571@infradead.org>
Date: Wed, 24 Sep 2025 10:00:00 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: jpoimboe@...nel.org,
 rostedt@...nel.org
Cc: linux-kernel@...r.kernel.org,
 peterz@...radead.org,
 "Steven Rostedt (Google)" <rostedt@...dmis.org>
Subject: [PATCH 12/12] unwind_user/x86: Enable frame pointer unwinding on x86

From: Josh Poimboeuf <jpoimboe@...nel.org>

Use ARCH_INIT_USER_FP_FRAME to describe how frame pointers are unwound
on x86, and enable CONFIG_HAVE_UNWIND_USER_FP accordingly so the
unwind_user interfaces can be used.

Signed-off-by: Josh Poimboeuf <jpoimboe@...nel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 arch/x86/Kconfig                   |    1 +
 arch/x86/include/asm/ptrace.h      |    9 +++++++++
 arch/x86/include/asm/unwind_user.h |   11 +++++++++++
 3 files changed, 21 insertions(+)
 create mode 100644 arch/x86/include/asm/unwind_user.h

--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -297,6 +297,7 @@ config X86
 	select HAVE_SYSCALL_TRACEPOINTS
 	select HAVE_UACCESS_VALIDATION		if HAVE_OBJTOOL
 	select HAVE_UNSTABLE_SCHED_CLOCK
+	select HAVE_UNWIND_USER_FP		if X86_64
 	select HAVE_USER_RETURN_NOTIFIER
 	select HAVE_GENERIC_VDSO
 	select VDSO_GETRANDOM			if X86_64
--- a/arch/x86/include/asm/ptrace.h
+++ b/arch/x86/include/asm/ptrace.h
@@ -255,6 +255,15 @@ static inline bool any_64bit_mode(struct
 #endif
 }
 
+static inline bool compat_user_mode(struct pt_regs *regs)
+{
+#ifdef CONFIG_X86_64
+	return !user_64bit_mode(regs);
+#else
+	return false;
+#endif
+}
+
 #ifdef CONFIG_X86_64
 #define current_user_stack_pointer()	current_pt_regs()->sp
 #define compat_user_stack_pointer()	current_pt_regs()->sp
--- /dev/null
+++ b/arch/x86/include/asm/unwind_user.h
@@ -0,0 +1,11 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_X86_UNWIND_USER_H
+#define _ASM_X86_UNWIND_USER_H
+
+#define ARCH_INIT_USER_FP_FRAME				\
+	.cfa_off	=  2,				\
+	.ra_off		= -1,				\
+	.fp_off		= -2,				\
+	.use_fp		= true,
+
+#endif /* _ASM_X86_UNWIND_USER_H */