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

Weinan Liu
2025-01-27T21:33:37Z

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@google.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