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Subject[PATCH 2/2] ppc64le save_stack_trace_tsk_reliable (Was: HAVE_RELIABLE_STACKTRACE)
On Tue, Dec 12, 2017 at 01:12:37PM +0100, Miroslav Benes wrote:
>
> I think that this is not enough. You need to also implement
> save_stack_trace_tsk_reliable() for powerpc defined as __weak in
> kernel/stacktrace.c.

So here is my initial proposal. I'd really like to get the successful
exit stricter, i.e. hit the initial stack value exactly instead of just
a window. Also, the check for kernel code looks clumsy IMHO. IOW:
Comments more than welcome!

Most of it is Copy&Waste, nonetheless:

Signed-off-by: Torsten Duwe <duwe@suse.de>


diff --git a/arch/powerpc/kernel/stacktrace.c b/arch/powerpc/kernel/stacktrace.c
index d534ed901538..e08af49e71d0 100644
--- a/arch/powerpc/kernel/stacktrace.c
+++ b/arch/powerpc/kernel/stacktrace.c
@@ -13,6 +13,7 @@
#include <linux/export.h>
#include <linux/sched.h>
#include <linux/sched/debug.h>
+#include <linux/sched/task_stack.h>
#include <linux/stacktrace.h>
#include <asm/ptrace.h>
#include <asm/processor.h>
@@ -76,3 +77,58 @@ save_stack_trace_regs(struct pt_regs *regs, struct stack_trace *trace)
save_context_stack(trace, regs->gpr[1], current, 0);
}
EXPORT_SYMBOL_GPL(save_stack_trace_regs);
+
+#ifdef CONFIG_HAVE_RELIABLE_STACKTRACE
+int
+save_stack_trace_tsk_reliable(struct task_struct *tsk,
+ struct stack_trace *trace)
+{
+ unsigned long sp;
+ unsigned long stack_page = (unsigned long)task_stack_page(tsk);
+ /* the last frame (unwinding first) may not yet have saved its LR onto the stack. */
+ int firstframe = 1;
+
+ if (tsk == current)
+ sp = current_stack_pointer();
+ else
+ sp = tsk->thread.ksp;
+
+ if (sp < stack_page + sizeof(struct thread_struct)
+ || sp > stack_page + THREAD_SIZE - STACK_FRAME_OVERHEAD)
+ return 1;
+
+ for (;;) {
+ unsigned long *stack = (unsigned long *) sp;
+ unsigned long newsp, ip;
+
+ newsp = stack[0];
+ /* Stack grows downwards; unwinder may only go up */
+ if (newsp <= sp)
+ return 1;
+
+ if (newsp >= stack_page + THREAD_SIZE)
+ return 1; /* invalid backlink, too far up! */
+
+ /* Examine the saved LR: it must point into kernel code. */
+ ip = stack[STACK_FRAME_LR_SAVE];
+ if ( (ip & 0xEFFF000000000000) != CONFIG_KERNEL_START
+ && !firstframe)
+ return 1;
+ firstframe = 0;
+
+ if (!trace->skip)
+ trace->entries[trace->nr_entries++] = ip;
+ else
+ trace->skip--;
+
+ if (newsp > stack_page + THREAD_SIZE - STACK_FRAME_OVERHEAD)
+ break; /* hit the window for last frame */
+
+ if (trace->nr_entries >= trace->max_entries)
+ return -E2BIG;
+
+ sp = newsp;
+ }
+ return 0;
+}
+#endif /* CONFIG_HAVE_RELIABLE_STACKTRACE */
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