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The following patch adds the x86_64 architecture specific implementation for function return probes. Function return probes is a mechanism built on top of kprobes that allows a caller to register a handler to be called when a given function exits. For example, to instrument the return path of sys_mkdir: static int sys_mkdir_exit(struct kretprobe_instance *i, struct pt_regs *regs) { printk("sys_mkdir exited\n"); return 0; } static struct kretprobe return_probe = { .handler = sys_mkdir_exit, }; <inside setup function> return_probe.kp.addr = (kprobe_opcode_t *) kallsyms_lookup_name("sys_mkdir"); if (register_kretprobe(&return_probe)) { printk(KERN_DEBUG "Unable to register return probe!\n"); /* do error path */ } <inside cleanup function> unregister_kretprobe(&return_probe); The way this works is that: * At system initialization time, kernel/kprobes.c installs a kprobe on a function called kretprobe_trampoline() that is implemented in the arch/x86_64/kernel/kprobes.c (More on this later) * When a return probe is registered using register_kretprobe(), kernel/kprobes.c will install a kprobe on the first instruction of the targeted function with the pre handler set to arch_prepare_kretprobe() which is implemented in arch/x86_64/kernel/kprobes.c. * arch_prepare_kretprobe() will prepare a kretprobe instance that stores: - nodes for hanging this instance in an empty or free list - a pointer to the return probe - the original return address - a pointer to the stack address With all this stowed away, arch_prepare_kretprobe() then sets the return address for the targeted function to a special trampoline function called kretprobe_trampoline() implemented in arch/x86_64/kernel/kprobes.c * The kprobe completes as normal, with control passing back to the target function that executes as normal, and eventually returns to our trampoline function. * Since a kprobe was installed on kretprobe_trampoline() during system initialization, control passes back to kprobes via the architecture specific function trampoline_probe_handler() which will lookup the instance in an hlist maintained by kernel/kprobes.c, and then call the handler function. * When trampoline_probe_handler() is done, the kprobes infrastructure single steps the original instruction (in this case just a top), and then calls trampoline_post_handler(). trampoline_post_handler() then looks up the instance again, puts the instance back on the free list, and then makes a long jump back to the original return instruction. So to recap, to instrument the exit path of a function this implementation will cause four interruptions: - A breakpoint at the very beginning of the function allowing us to switch out the return address - A single step interruption to execute the original instruction that we replaced with the break instruction (normal kprobe flow) - A breakpoint in the trampoline function where our instrumented function returned to - A single step interruption to execute the original instruction that we replaced with the break instruction (normal kprobe flow) Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
67 lines
2.2 KiB
C
67 lines
2.2 KiB
C
#ifndef _ASM_KPROBES_H
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#define _ASM_KPROBES_H
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/*
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* Kernel Probes (KProbes)
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* include/asm-x86_64/kprobes.h
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
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*
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* Copyright (C) IBM Corporation, 2002, 2004
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*
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* 2004-Oct Prasanna S Panchamukhi <prasanna@in.ibm.com> and Jim Keniston
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* kenistoj@us.ibm.com adopted from i386.
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*/
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#include <linux/types.h>
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#include <linux/ptrace.h>
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struct pt_regs;
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typedef u8 kprobe_opcode_t;
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#define BREAKPOINT_INSTRUCTION 0xcc
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#define MAX_INSN_SIZE 15
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#define MAX_STACK_SIZE 64
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#define MIN_STACK_SIZE(ADDR) (((MAX_STACK_SIZE) < \
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(((unsigned long)current_thread_info()) + THREAD_SIZE - (ADDR))) \
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? (MAX_STACK_SIZE) \
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: (((unsigned long)current_thread_info()) + THREAD_SIZE - (ADDR)))
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#define JPROBE_ENTRY(pentry) (kprobe_opcode_t *)pentry
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#define ARCH_SUPPORTS_KRETPROBES
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void kretprobe_trampoline(void);
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/* Architecture specific copy of original instruction*/
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struct arch_specific_insn {
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/* copy of the original instruction */
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kprobe_opcode_t *insn;
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};
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/* trap3/1 are intr gates for kprobes. So, restore the status of IF,
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* if necessary, before executing the original int3/1 (trap) handler.
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*/
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static inline void restore_interrupts(struct pt_regs *regs)
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{
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if (regs->eflags & IF_MASK)
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local_irq_enable();
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}
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extern int post_kprobe_handler(struct pt_regs *regs);
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extern int kprobe_fault_handler(struct pt_regs *regs, int trapnr);
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extern int kprobe_handler(struct pt_regs *regs);
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extern int kprobe_exceptions_notify(struct notifier_block *self,
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unsigned long val, void *data);
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#endif /* _ASM_KPROBES_H */
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