sh: Check for return_to_handler when unwinding the stack (60339fad) · Commits · 戴 / test

When CONFIG_FUNCTION_GRAPH_TRACER is enabled the function graph tracer may patch return addresses on the stack with the address of return_to_handler(). This really confuses the DWARF unwinder because it will try find the caller of return_to_handler(), not the caller of the real return address. So teach the DWARF unwinder how to find the real return address whenever it encounters return_to_handler(). This patch does not cope very well when multiple return addresses on the stack have been patched. To make it work properly it would require state to track how many return_to_handler()'s have been seen so that we'd know where to look in current->curr_ret_stack[]. So for now, instead of trying to handle this, just moan if more than one return address on the stack has been patched. Signed-off-by:

Matt Fleming <matt@console-pimps.org> Signed-off-by:

Paul Mundt <lethal@linux-sh.org>

arch/sh/kernel/dwarf.c

+22 −0

Original line number	Diff line number	Diff line
		@@ -20,6 +20,7 @@
		#include <linux/list.h>
		#include <linux/mempool.h>
		#include <linux/mm.h>
		#include <linux/ftrace.h>
		#include <asm/dwarf.h>
		#include <asm/unwinder.h>
		#include <asm/sections.h>
		@@ -557,6 +558,27 @@ struct dwarf_frame * dwarf_unwind_stack(unsigned long pc,
		if (!pc && !prev)
		pc = (unsigned long)current_text_addr();

		#ifdef CONFIG_FUNCTION_GRAPH_TRACER
		/*
		* If our stack has been patched by the function graph tracer
		* then we might see the address of return_to_handler() where we
		* expected to find the real return address.
		*/
		if (pc == (unsigned long)&return_to_handler) {
		int index = current->curr_ret_stack;

		/*
		* We currently have no way of tracking how many
		* return_to_handler()'s we've seen. If there is more
		* than one patched return address on our stack,
		* complain loudly.
		*/
		WARN_ON(index > 0);

		pc = current->ret_stack[index].ret;
		}
		#endif

		frame = mempool_alloc(dwarf_frame_pool, GFP_ATOMIC);
		if (!frame) {
		printk(KERN_ERR "Unable to allocate a dwarf frame\n");

Admin message