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This patch adds function-return probes to kprobes for the i386
architecture. This enables you to establish a handler to be run when a
function returns.
1. API
Two new functions are added to kprobes:
int register_kretprobe(struct kretprobe *rp);
void unregister_kretprobe(struct kretprobe *rp);
2. Registration and unregistration
2.1 Register
To register a function-return probe, the user populates the following
fields in a kretprobe object and calls register_kretprobe() with the
kretprobe address as an argument:
kp.addr - the function's address
handler - this function is run after the ret instruction executes, but
before control returns to the return address in the caller.
maxactive - The maximum number of instances of the probed function that
can be active concurrently. For example, if the function is non-
recursive and is called with a spinlock or mutex held, maxactive = 1
should be enough. If the function is non-recursive and can never
relinquish the CPU (e.g., via a semaphore or preemption), NR_CPUS should
be enough. maxactive is used to determine how many kretprobe_instance
objects to allocate for this particular probed function. If maxactive <=
0, it is set to a default value (if CONFIG_PREEMPT maxactive=max(10, 2 *
NR_CPUS) else maxactive=NR_CPUS)
For example:
struct kretprobe rp;
rp.kp.addr = /* entrypoint address */
rp.handler = /*return probe handler */
rp.maxactive = /* e.g., 1 or NR_CPUS or 0, see the above explanation */
register_kretprobe(&rp);
The following field may also be of interest:
nmissed - Initialized to zero when the function-return probe is
registered, and incremented every time the probed function is entered but
there is no kretprobe_instance object available for establishing the
function-return probe (i.e., because maxactive was set too low).
2.2 Unregister
To unregiter a function-return probe, the user calls
unregister_kretprobe() with the same kretprobe object as registered
previously. If a probed function is running when the return probe is
unregistered, the function will return as expected, but the handler won't
be run.
3. Limitations
3.1 This patch supports only the i386 architecture, but patches for
x86_64 and ppc64 are anticipated soon.
3.2 Return probes operates by replacing the return address in the stack
(or in a known register, such as the lr register for ppc). This may
cause __builtin_return_address(0), when invoked from the return-probed
function, to return the address of the return-probes trampoline.
3.3 This implementation uses the "Multiprobes at an address" feature in
2.6.12-rc3-mm3.
3.4 Due to a limitation in multi-probes, you cannot currently establish
a return probe and a jprobe on the same function. A patch to remove
this limitation is being tested.
This feature is required by SystemTap (http://sourceware.org/systemtap),
and reflects ideas contributed by several SystemTap developers, including
Will Cohen and Ananth Mavinakayanahalli.
Signed-off-by: Hien Nguyen <hien@us.ibm.com>
Signed-off-by: Prasanna S Panchamukhi <prasanna@in.ibm.com>
Signed-off-by: Frederik Deweerdt <frederik.deweerdt@laposte.net>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
73 lines
2.2 KiB
C
73 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-i386/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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* 2002-Oct Created by Vamsi Krishna S <vamsi_krishna@in.ibm.com> Kernel
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* Probes initial implementation ( includes suggestions from
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* Rusty Russell).
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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 16
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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[MAX_INSN_SIZE];
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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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#ifdef CONFIG_KPROBES
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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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#else /* !CONFIG_KPROBES */
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static inline int kprobe_exceptions_notify(struct notifier_block *self,
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unsigned long val, void *data)
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{
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return 0;
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}
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#endif
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#endif /* _ASM_KPROBES_H */
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