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>
---
 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 f938b957a927..08c44db0fefb 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -291,6 +291,7 @@ 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 */
-- 
2.48.1