linux-kernel - Re: [PATCH v3] tracing: Function stack size and its name mismatch in arm64

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Date:   Fri, 2 Aug 2019 12:11:24 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Jiping Ma <jiping.ma2@...driver.com>
Cc:     <mingo@...hat.com>, <catalin.marinas@....com>,
        <will.deacon@....com>, <joel@...lfernandes.org>,
        <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v3] tracing: Function stack size and its name mismatch
 in arm64

On Fri, 2 Aug 2019 12:09:20 -0400
Steven Rostedt <rostedt@...dmis.org> wrote:

> On Fri, 2 Aug 2019 11:22:59 -0400
> Steven Rostedt <rostedt@...dmis.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)) {