The following commit has been merged in the linux branch: commit 60339fad5c68c9c533cd14e67194ff8f727c41d9 Author: Matt Fleming matt@console-pimps.org Date: Sat Oct 24 18:56:57 2009 +0000

sh: Check for return_to_handler when unwinding the stack

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

diff --git a/arch/sh/kernel/dwarf.c b/arch/sh/kernel/dwarf.c index 03b3616..2d07084 100644 --- a/arch/sh/kernel/dwarf.c +++ b/arch/sh/kernel/dwarf.c @@ -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");