arm64: use a common struct frame_record

Currently the signal handling code has its own struct frame_record,
the definition of struct pt_regs open-codes a frame record as an array,
and the kernel unwinder hard-codes frame record offsets.

Move to a common struct frame_record that can be used throughout the
kernel.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Mark Brown <broonie@kernel.org>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Reviewed-by: Puranjay Mohan <puranjay12@gmail.com>
Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: Kalesh Singh <kaleshsingh@google.com>
Cc: Madhavan T. Venkataraman <madvenka@linux.microsoft.com>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/20241017092538.1859841-6-mark.rutland@arm.com
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

Author: mrutland-arm

arch/arm64/include/asm/ptrace.h

@@ -98,6 +98,8 @@
 #include <linux/bug.h>
 #include <linux/types.h>
 
+#include <asm/stacktrace/frame.h>
+
 /* sizeof(struct user) for AArch32 */
 #define COMPAT_USER_SZ	296
 
@@ -168,7 +170,7 @@ struct pt_regs {
 	u64 sdei_ttbr1;
 	u64 unused;
 
-	u64 stackframe[2];
+	struct frame_record stackframe;
 
 	/* Only valid for some EL1 exceptions. */
 	u64 lockdep_hardirqs;

arch/arm64/include/asm/stacktrace/common.h

@@ -137,21 +137,23 @@ static inline int unwind_consume_stack(struct unwind_state *state,
 static inline int
 unwind_next_frame_record(struct unwind_state *state)
 {
+	struct frame_record *record;
 	unsigned long fp = state->fp;
 	int err;
 
 	if (fp & 0x7)
 		return -EINVAL;
 
-	err = unwind_consume_stack(state, fp, 16);
+	err = unwind_consume_stack(state, fp, sizeof(*record));
 	if (err)
 		return err;
 
 	/*
 	 * Record this frame record's values.
 	 */
-	state->fp = READ_ONCE(*(unsigned long *)(fp));
-	state->pc = READ_ONCE(*(unsigned long *)(fp + 8));
+	record = (struct frame_record *)fp;
+	state->fp = READ_ONCE(record->fp);
+	state->pc = READ_ONCE(record->lr);
 
 	return 0;
 }

arch/arm64/include/asm/stacktrace/frame.h

@@ -0,0 +1,13 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+#ifndef __ASM_STACKTRACE_FRAME_H
+#define __ASM_STACKTRACE_FRAME_H
+
+/*
+ * A standard AAPCS64 frame record.
+ */
+struct frame_record {
+	u64 fp;
+	u64 lr;
+};
+
+#endif /* __ASM_STACKTRACE_FRAME_H */

arch/arm64/kernel/process.c

@@ -419,7 +419,7 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args)
 	 * For the benefit of the unwinder, set up childregs->stackframe
 	 * as the final frame for the new task.
 	 */
-	p->thread.cpu_context.fp = (unsigned long)childregs->stackframe;
+	p->thread.cpu_context.fp = (unsigned long)&childregs->stackframe;
 
 	ptrace_hw_copy_thread(p);
 

arch/arm64/kernel/signal.c

@@ -42,11 +42,6 @@ struct rt_sigframe {
 	struct ucontext uc;
 };
 
-struct frame_record {
-	u64 fp;
-	u64 lr;
-};
-
 struct rt_sigframe_user_layout {
 	struct rt_sigframe __user *sigframe;
 	struct frame_record __user *next_frame;

arch/arm64/kernel/stacktrace.c

@@ -145,7 +145,7 @@ kunwind_next(struct kunwind_state *state)
 	int err;
 
 	/* Final frame; nothing to unwind */
-	if (fp == (unsigned long)task_pt_regs(tsk)->stackframe)
+	if (fp == (unsigned long)&task_pt_regs(tsk)->stackframe)
 		return -ENOENT;
 
 	err = unwind_next_frame_record(&state->common);