linux-kernel - [PATCH 5/8] unwind: arm64: Add sframe unwinder on arm64

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Message-ID: <20250127213310.2496133-6-wnliu@google.com>
Date: Mon, 27 Jan 2025 21:33:07 +0000
From: Weinan Liu <wnliu@...gle.com>
To: Josh Poimboeuf <jpoimboe@...nel.org>, Steven Rostedt <rostedt@...dmis.org>, 
	Indu Bhagat <indu.bhagat@...cle.com>, Peter Zijlstra <peterz@...radead.org>
Cc: Mark Rutland <mark.rutland@....com>, roman.gushchin@...ux.dev, 
	Will Deacon <will@...nel.org>, Ian Rogers <irogers@...gle.com>, linux-toolchains@...r.kernel.org, 
	linux-kernel@...r.kernel.org, live-patching@...r.kernel.org, 
	joe.lawrence@...hat.com, linux-arm-kernel@...ts.infradead.org, 
	Weinan Liu <wnliu@...gle.com>
Subject: [PATCH 5/8] unwind: arm64: Add sframe unwinder on arm64

Add unwind_next_frame_sframe() function to unwind by sframe info.
Built with GNU Binutils 2.42 to verify that this sframe unwinder can
backtrace correctly on arm64.

Signed-off-by: Weinan Liu <wnliu@...gle.com>
---
 arch/arm64/include/asm/stacktrace/common.h |  4 ++
 arch/arm64/kernel/setup.c                  |  2 +
 arch/arm64/kernel/stacktrace.c             | 59 ++++++++++++++++++++++
 3 files changed, 65 insertions(+)

diff --git a/arch/arm64/include/asm/stacktrace/common.h b/arch/arm64/include/asm/stacktrace/common.h
index 821a8fdd31af..19edae8a5b1a 100644
--- a/arch/arm64/include/asm/stacktrace/common.h
+++ b/arch/arm64/include/asm/stacktrace/common.h
@@ -25,6 +25,7 @@ struct stack_info {
  * @stack:       The stack currently being unwound.
  * @stacks:      An array of stacks which can be unwound.
  * @nr_stacks:   The number of stacks in @stacks.
+ * @cfa:         The sp value at the call site of the current function.
  */
 struct unwind_state {
 	unsigned long fp;
@@ -33,6 +34,9 @@ struct unwind_state {
 	struct stack_info stack;
 	struct stack_info *stacks;
 	int nr_stacks;
+#ifdef CONFIG_SFRAME_UNWINDER
+	unsigned long cfa;
+#endif
 };
 
 static inline struct stack_info stackinfo_get_unknown(void)
diff --git a/arch/arm64/kernel/setup.c b/arch/arm64/kernel/setup.c
index 4f613e8e0745..d3ac92b624f3 100644
--- a/arch/arm64/kernel/setup.c
+++ b/arch/arm64/kernel/setup.c
@@ -32,6 +32,7 @@
 #include <linux/sched/task.h>
 #include <linux/scs.h>
 #include <linux/mm.h>
+#include <linux/sframe_lookup.h>
 
 #include <asm/acpi.h>
 #include <asm/fixmap.h>
@@ -377,6 +378,7 @@ void __init __no_sanitize_address setup_arch(char **cmdline_p)
 			"This indicates a broken bootloader or old kernel\n",
 			boot_args[1], boot_args[2], boot_args[3]);
 	}
+	init_sframe_table();
 }
 
 static inline bool cpu_can_disable(unsigned int cpu)
diff --git a/arch/arm64/kernel/stacktrace.c b/arch/arm64/kernel/stacktrace.c
index 1d9d51d7627f..c035adb8fe8a 100644
--- a/arch/arm64/kernel/stacktrace.c
+++ b/arch/arm64/kernel/stacktrace.c
@@ -14,6 +14,7 @@
 #include <linux/sched/debug.h>
 #include <linux/sched/task_stack.h>
 #include <linux/stacktrace.h>
+#include <linux/sframe_lookup.h>
 
 #include <asm/efi.h>
 #include <asm/irq.h>
@@ -242,6 +243,53 @@ kunwind_next_frame_record(struct kunwind_state *state)
 	return 0;
 }
 
+#ifdef CONFIG_SFRAME_UNWINDER
+/*
+ * Unwind to the next frame according to sframe.
+ */
+static __always_inline int
+unwind_next_frame_sframe(struct unwind_state *state)
+{
+	unsigned long fp = state->fp, ip = state->pc;
+	unsigned long base_reg, cfa;
+	unsigned long pc_addr, fp_addr;
+	struct sframe_ip_entry entry;
+	struct stack_info *info;
+	struct frame_record *record = (struct frame_record *)fp;
+
+	int err;
+
+	/* frame record alignment 8 bytes */
+	if (fp & 0x7)
+		return -EINVAL;
+
+	info = unwind_find_stack(state, fp, sizeof(*record));
+	if (!info)
+		return -EINVAL;
+
+	err = sframe_find_pc(ip, &entry);
+	if (err)
+		return -EINVAL;
+
+	unwind_consume_stack(state, info, fp, sizeof(*record));
+
+	base_reg = entry.use_fp ? fp : state->cfa;
+
+	/* Set up the initial CFA using fp based info if CFA is not set */
+	if (!state->cfa)
+		cfa = fp - entry.fp_offset;
+	else
+		cfa = base_reg + entry.cfa_offset;
+	fp_addr = cfa + entry.fp_offset;
+	pc_addr = cfa + entry.ra_offset;
+	state->cfa = cfa;
+	state->fp = READ_ONCE(*(unsigned long *)(fp_addr));
+	state->pc = READ_ONCE(*(unsigned long *)(pc_addr));
+
+	return 0;
+}
+#endif
+
 /*
  * Unwind from one frame record (A) to the next frame record (B).
  *
@@ -261,7 +309,15 @@ kunwind_next(struct kunwind_state *state)
 	case KUNWIND_SOURCE_CALLER:
 	case KUNWIND_SOURCE_TASK:
 	case KUNWIND_SOURCE_REGS_PC:
+#ifdef CONFIG_SFRAME_UNWINDER
+	err = unwind_next_frame_sframe(&state->common);
+
+	/* Fallback to FP based unwinder */
+	if (err)
 		err = kunwind_next_frame_record(state);
+#else
+	err = kunwind_next_frame_record(state);
+#endif
 		break;
 	default:
 		err = -EINVAL;
@@ -347,6 +403,9 @@ kunwind_stack_walk(kunwind_consume_fn consume_state,
 		.common = {
 			.stacks = stacks,
 			.nr_stacks = ARRAY_SIZE(stacks),
+#ifdef CONFIG_SFRAME_UNWINDER
+			.cfa = 0,
+#endif
 		},
 	};
 
-- 
2.48.1.262.g85cc9f2d1e-goog