[PATCH v15 1/6] arm64: Split unwind_init()

madvenka
2022-06-17T21:12:34Z

From: "Madhavan T. Venkataraman" <madvenka@linux.microsoft.com>

unwind_init() is currently a single function that initializes all of the
unwind state. Split it into the following functions and call them
appropriately:

- unwind_init_from_regs() - initialize from regs passed by caller.

- unwind_init_from_caller() - initialize for the current task
from the caller of arch_stack_walk().

- unwind_init_from_task() - initialize from the saved state of a
task other than the current task. In this case, the other
task must not be running.

This is done for two reasons:

- the different ways of initializing are clear

- specialized code can be added to each initializer in the future.

Signed-off-by: Madhavan T. Venkataraman <madvenka@linux.microsoft.com>
Reviewed-by: Mark Brown <broonie@kernel.org>
---
arch/arm64/kernel/stacktrace.c | 66 ++++++++++++++++++++++++++++------
1 file changed, 55 insertions(+), 11 deletions(-)

diff --git a/arch/arm64/kernel/stacktrace.c b/arch/arm64/kernel/stacktrace.c
index 0467cb79f080..e44f93ff25f0 100644
--- a/arch/arm64/kernel/stacktrace.c
+++ b/arch/arm64/kernel/stacktrace.c
@@ -50,11 +50,8 @@ struct unwind_state {
#endif
};

-static notrace void unwind_init(struct unwind_state *state, unsigned long fp,
- unsigned long pc)
+static void unwind_init_common(struct unwind_state *state)
{
- state->fp = fp;
- state->pc = pc;
#ifdef CONFIG_KRETPROBES
state->kr_cur = NULL;
#endif
@@ -72,7 +69,57 @@ static notrace void unwind_init(struct unwind_state *state, unsigned long fp,
state->prev_fp = 0;
state->prev_type = STACK_TYPE_UNKNOWN;
}
-NOKPROBE_SYMBOL(unwind_init);
+
+/*
+ * Start an unwind from a pt_regs.
+ *
+ * The unwind will begin at the PC within the regs.
+ *
+ * The regs must be on a stack currently owned by the calling task.
+ */
+static inline void unwind_init_from_regs(struct unwind_state *state,
+ struct pt_regs *regs)
+{
+ unwind_init_common(state);
+
+ state->fp = regs->regs[29];
+ state->pc = regs->pc;
+}
+
+/*
+ * Start an unwind from a caller.
+ *
+ * The unwind will begin at the caller of whichever function this is inlined
+ * into.
+ *
+ * The function which invokes this must be noinline.
+ */
+static __always_inline void unwind_init_from_caller(struct unwind_state *state)
+{
+ unwind_init_common(state);
+
+ state->fp = (unsigned long)__builtin_frame_address(1);
+ state->pc = (unsigned long)__builtin_return_address(0);
+}
+
+/*
+ * Start an unwind from a blocked task.
+ *
+ * The unwind will begin at the blocked tasks saved PC (i.e. the caller of
+ * cpu_switch_to()).
+ *
+ * The caller should ensure the task is blocked in cpu_switch_to() for the
+ * duration of the unwind, or the unwind will be bogus. It is never valid to
+ * call this for the current task.
+ */
+static inline void unwind_init_from_task(struct unwind_state *state,
+ struct task_struct *task)
+{
+ unwind_init_common(state);
+
+ state->fp = thread_saved_fp(task);
+ state->pc = thread_saved_pc(task);
+}

/*
* Unwind from one frame record (A) to the next frame record (B).
@@ -213,14 +260,11 @@ noinline notrace void arch_stack_walk(stack_trace_consume_fn consume_entry,
struct unwind_state state;

if (regs)
- unwind_init(&state, regs->regs[29], regs->pc);
+ unwind_init_from_regs(&state, regs);
else if (task == current)
- unwind_init(&state,
- (unsigned long)__builtin_frame_address(1),
- (unsigned long)__builtin_return_address(0));
+ unwind_init_from_caller(&state);
else
- unwind_init(&state, thread_saved_fp(task),
- thread_saved_pc(task));
+ unwind_init_from_task(&state, task);

unwind(task, &state, consume_entry, cookie);
}
--
2.25.1