backtrace.c

xen虚拟机源代码安装包

/**
 * @file backtrace.c
 *
 * @remark Copyright 2002 OProfile authors
 * @remark Read the file COPYING
 *
 * @author John Levon
 * @author David Smith
 * Modified for Xen by Amitabha Roy
 *
 */

#include<xen/types.h>
#include<asm/page.h>
#include<xen/xenoprof.h>
#include<asm/guest_access.h>

struct frame_head {
	struct frame_head * ebp;
	unsigned long ret;
} __attribute__((packed));

static struct frame_head *
dump_hypervisor_backtrace(struct domain *d, struct vcpu *vcpu, 
			  struct frame_head * head, int mode)
{
	if (!xenoprof_add_trace(d, vcpu, head->ret, mode))
		return 0;

	/* frame pointers should strictly progress back up the stack
	 * (towards higher addresses) */
	if (head >= head->ebp)
		return NULL;

	return head->ebp;
}

static struct frame_head *
dump_guest_backtrace(struct domain *d, struct vcpu *vcpu, 
		     struct frame_head * head, int mode)
{
	struct frame_head bufhead[2];
	XEN_GUEST_HANDLE(char) guest_head = guest_handle_from_ptr(head, char);
	
	/* Also check accessibility of one struct frame_head beyond */
	if (!guest_handle_okay(guest_head, sizeof(bufhead)))
		return 0;
	if (__copy_from_guest_offset((char *)bufhead, guest_head, 0, 
	    sizeof(bufhead)))
		return 0;

	if (!xenoprof_add_trace(d, vcpu, bufhead[0].ret, mode))
	    return 0;

	/* frame pointers should strictly progress back up the stack
	 * (towards higher addresses) */
	if (head >= bufhead[0].ebp)
		return NULL;

	return bufhead[0].ebp;
}

/*
 * |             | /\ Higher addresses
 * |             |
 * --------------- stack base (address of current_thread_info)
 * | thread info |
 * .             .
 * |    stack    |
 * --------------- saved regs->ebp value if valid (frame_head address)
 * .             .
 * --------------- saved regs->rsp value if x86_64
 * |             |
 * --------------- struct pt_regs * stored on stack if 32-bit
 * |             |
 * .             .
 * |             |
 * --------------- %esp
 * |             |
 * |             | \/ Lower addresses
 *
 * Thus, regs (or regs->rsp for x86_64) <-> stack base restricts the
 * valid(ish) ebp values. Note: (1) for x86_64, NMI and several other
 * exceptions use special stacks, maintained by the interrupt stack table
 * (IST). These stacks are set up in trap_init() in
 * arch/x86_64/kernel/traps.c. Thus, for x86_64, regs now does not point
 * to the kernel stack; instead, it points to some location on the NMI
 * stack. On the other hand, regs->rsp is the stack pointer saved when the
 * NMI occurred. (2) For 32-bit, regs->esp is not valid because the
 * processor does not save %esp on the kernel stack when interrupts occur
 * in the kernel mode.
 */
#if defined(CONFIG_FRAME_POINTER)
static int valid_hypervisor_stack(struct frame_head * head, 
				  struct cpu_user_regs * regs)
{
	unsigned long headaddr = (unsigned long)head;
#ifdef CONFIG_X86_64
	unsigned long stack = (unsigned long)regs->rsp;
#else
	unsigned long stack = (unsigned long)regs;
#endif
	unsigned long stack_base = (stack & ~(STACK_SIZE - 1)) + STACK_SIZE;

	return headaddr > stack && headaddr < stack_base;
}
#else
/* without fp, it's just junk */
static int valid_hypervisor_stack(struct frame_head * head, 
				  struct cpu_user_regs * regs)
{
	return 0;
}
#endif

void xenoprof_backtrace(struct domain *d, struct vcpu *vcpu, 
			struct cpu_user_regs * const regs,
			unsigned long depth, int mode)
{
	struct frame_head *head;

	head = (struct frame_head *)regs->ebp;

	if (mode > 1) {
		while (depth-- && valid_hypervisor_stack(head, regs))
		    head = dump_hypervisor_backtrace(d, vcpu, head, mode);
		return;
	}

	while (depth-- && head)
	    head = dump_guest_backtrace(d, vcpu, head, mode);
}