[PATCH v6 06/18] unwind_user/x86: Enable compat mode frame pointer unwinding on x86

Steven Rostedt
2025-04-25T14:56:14Z

Use ARCH_INIT_USER_COMPAT_FP_FRAME to describe how frame pointers are
unwound on x86, and implement the hooks needed to add the segment base
addresses. Enable HAVE_UNWIND_USER_COMPAT_FP if the system has compat
mode compiled in.

Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
arch/x86/Kconfig | 1 +
arch/x86/include/asm/unwind_user.h | 50 ++++++++++++++++++++++++
arch/x86/include/asm/unwind_user_types.h | 17 ++++++++
3 files changed, 68 insertions(+)
create mode 100644 arch/x86/include/asm/unwind_user_types.h

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index b5a85d2be5ee..35d3b01b65c6 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -301,6 +301,7 @@ config X86
select HAVE_SYSCALL_TRACEPOINTS
select HAVE_UACCESS_VALIDATION if HAVE_OBJTOOL
select HAVE_UNSTABLE_SCHED_CLOCK
+ select HAVE_UNWIND_USER_COMPAT_FP if IA32_EMULATION
select HAVE_UNWIND_USER_FP if X86_64
select HAVE_USER_RETURN_NOTIFIER
select HAVE_GENERIC_VDSO
diff --git a/arch/x86/include/asm/unwind_user.h b/arch/x86/include/asm/unwind_user.h
index 8597857bf896..bb1148111259 100644
--- a/arch/x86/include/asm/unwind_user.h
+++ b/arch/x86/include/asm/unwind_user.h
@@ -2,10 +2,60 @@
#ifndef _ASM_X86_UNWIND_USER_H
#define _ASM_X86_UNWIND_USER_H

+#include <linux/unwind_user_types.h>
+#include <asm/ptrace.h>
+#include <asm/perf_event.h>
+
#define ARCH_INIT_USER_FP_FRAME \
.cfa_off = (s32)sizeof(long) * 2, \
.ra_off = (s32)sizeof(long) * -1, \
.fp_off = (s32)sizeof(long) * -2, \
.use_fp = true,

+#ifdef CONFIG_IA32_EMULATION
+
+#define ARCH_INIT_USER_COMPAT_FP_FRAME \
+ .cfa_off = (s32)sizeof(u32) * 2, \
+ .ra_off = (s32)sizeof(u32) * -1, \
+ .fp_off = (s32)sizeof(u32) * -2, \
+ .use_fp = true,
+
+#define in_compat_mode(regs) !user_64bit_mode(regs)
+
+static inline void arch_unwind_user_init(struct unwind_user_state *state,
+ struct pt_regs *regs)
+{
+ unsigned long cs_base, ss_base;
+
+ if (state->type != UNWIND_USER_TYPE_COMPAT_FP)
+ return;
+
+ scoped_guard(irqsave) {
+ cs_base = segment_base_address(regs->cs);
+ ss_base = segment_base_address(regs->ss);
+ }
+
+ state->arch.cs_base = cs_base;
+ state->arch.ss_base = ss_base;
+
+ state->ip += cs_base;
+ state->sp += ss_base;
+ state->fp += ss_base;
+}
+#define arch_unwind_user_init arch_unwind_user_init
+
+static inline void arch_unwind_user_next(struct unwind_user_state *state)
+{
+ if (state->type != UNWIND_USER_TYPE_COMPAT_FP)
+ return;
+
+ state->ip += state->arch.cs_base;
+ state->fp += state->arch.ss_base;
+}
+#define arch_unwind_user_next arch_unwind_user_next
+
+#endif /* CONFIG_IA32_EMULATION */
+
+#include <asm-generic/unwind_user.h>
+
#endif /* _ASM_X86_UNWIND_USER_H */
diff --git a/arch/x86/include/asm/unwind_user_types.h b/arch/x86/include/asm/unwind_user_types.h
new file mode 100644
index 000000000000..d7074dc5f0ce
--- /dev/null
+++ b/arch/x86/include/asm/unwind_user_types.h
@@ -0,0 +1,17 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_UNWIND_USER_TYPES_H
+#define _ASM_UNWIND_USER_TYPES_H
+
+#ifdef CONFIG_IA32_EMULATION
+
+struct arch_unwind_user_state {
+ unsigned long ss_base;
+ unsigned long cs_base;
+};
+#define arch_unwind_user_state arch_unwind_user_state
+
+#endif /* CONFIG_IA32_EMULATION */
+
+#include <asm-generic/unwind_user_types.h>
+
+#endif /* _ASM_UNWIND_USER_TYPES_H */
--
2.47.2