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SubjectRe: [PATCH v3] tracing: Function stack size and its name mismatch in arm64
On Fri, 2 Aug 2019 12:09:20 -0400
Steven Rostedt <rostedt@goodmis.org> wrote:

> On Fri, 2 Aug 2019 11:22:59 -0400
> Steven Rostedt <rostedt@goodmis.org> wrote:
>
> > I think you are not explaining the issue correctly. From looking at the
> > document, I think what you want to say is that the LR is saved *after*
> > the data for the function. Is that correct? If so, then yes, it would
> > cause the stack tracing algorithm to be incorrect.
> >
>
> [..]
>
> > Can someone confirm that this is the real issue?
>
> Does this patch fix your issue?
>

Bah, I hit "attach" instead of "insert" (I wondered why it didn't
insert). Here's the patch without the attachment.

-- Steve

diff --git a/arch/arm64/include/asm/ftrace.h b/arch/arm64/include/asm/ftrace.h
index 5ab5200b2bdc..13a4832cfb00 100644
--- a/arch/arm64/include/asm/ftrace.h
+++ b/arch/arm64/include/asm/ftrace.h
@@ -13,6 +13,7 @@
#define HAVE_FUNCTION_GRAPH_FP_TEST
#define MCOUNT_ADDR ((unsigned long)_mcount)
#define MCOUNT_INSN_SIZE AARCH64_INSN_SIZE
+#define ARCH_RET_ADDR_AFTER_LOCAL_VARS 1

#ifndef __ASSEMBLY__
#include <linux/compat.h>
diff --git a/kernel/trace/trace_stack.c b/kernel/trace/trace_stack.c
index 5d16f73898db..050c6bd9beac 100644
--- a/kernel/trace/trace_stack.c
+++ b/kernel/trace/trace_stack.c
@@ -158,6 +158,18 @@ static void check_stack(unsigned long ip, unsigned long *stack)
i++;
}

+#ifdef ARCH_RET_ADDR_AFTER_LOCAL_VARS
+ /*
+ * Most archs store the return address before storing the
+ * function's local variables. But some archs do this backwards.
+ */
+ if (x > 1) {
+ memmove(&stack_trace_index[0], &stack_trace_index[1],
+ sizeof(stack_trace_index[0]) * (x - 1));
+ x--;
+ }
+#endif
+
stack_trace_nr_entries = x;

if (task_stack_end_corrupted(current)) {
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