| Anil S Keshavamurthy | b2761dc | 2005-06-23 00:09:28 -0700 | [diff] [blame] | 1 | /* |
| 2 | * Jprobe specific operations |
| 3 | * |
| 4 | * This program is free software; you can redistribute it and/or modify |
| 5 | * it under the terms of the GNU General Public License as published by |
| 6 | * the Free Software Foundation; either version 2 of the License, or |
| 7 | * (at your option) any later version. |
| 8 | * |
| 9 | * This program is distributed in the hope that it will be useful, |
| 10 | * but WITHOUT ANY WARRANTY; without even the implied warranty of |
| 11 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
| 12 | * GNU General Public License for more details. |
| 13 | * |
| 14 | * You should have received a copy of the GNU General Public License |
| 15 | * along with this program; if not, write to the Free Software |
| 16 | * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. |
| 17 | * |
| 18 | * Copyright (C) Intel Corporation, 2005 |
| 19 | * |
| 20 | * 2005-May Rusty Lynch <rusty.lynch@intel.com> and Anil S Keshavamurthy |
| 21 | * <anil.s.keshavamurthy@intel.com> initial implementation |
| 22 | * |
| 23 | * Jprobes (a.k.a. "jump probes" which is built on-top of kprobes) allow a |
| 24 | * probe to be inserted into the beginning of a function call. The fundamental |
| 25 | * difference between a jprobe and a kprobe is the jprobe handler is executed |
| 26 | * in the same context as the target function, while the kprobe handlers |
| 27 | * are executed in interrupt context. |
| 28 | * |
| 29 | * For jprobes we initially gain control by placing a break point in the |
| 30 | * first instruction of the targeted function. When we catch that specific |
| 31 | * break, we: |
| 32 | * * set the return address to our jprobe_inst_return() function |
| 33 | * * jump to the jprobe handler function |
| 34 | * |
| 35 | * Since we fixed up the return address, the jprobe handler will return to our |
| 36 | * jprobe_inst_return() function, giving us control again. At this point we |
| 37 | * are back in the parents frame marker, so we do yet another call to our |
| 38 | * jprobe_break() function to fix up the frame marker as it would normally |
| 39 | * exist in the target function. |
| 40 | * |
| 41 | * Our jprobe_return function then transfers control back to kprobes.c by |
| 42 | * executing a break instruction using one of our reserved numbers. When we |
| 43 | * catch that break in kprobes.c, we continue like we do for a normal kprobe |
| 44 | * by single stepping the emulated instruction, and then returning execution |
| 45 | * to the correct location. |
| 46 | */ |
| 47 | #include <asm/asmmacro.h> |
| 48 | |
| 49 | /* |
| 50 | * void jprobe_break(void) |
| 51 | */ |
| Prasanna S Panchamukhi | 1f7ad57 | 2005-09-06 15:19:30 -0700 | [diff] [blame] | 52 | .section .kprobes.text, "ax" |
| Anil S Keshavamurthy | b2761dc | 2005-06-23 00:09:28 -0700 | [diff] [blame] | 53 | ENTRY(jprobe_break) |
| 54 | break.m 0x80300 |
| 55 | END(jprobe_break) |
| 56 | |
| 57 | /* |
| 58 | * void jprobe_inst_return(void) |
| 59 | */ |
| 60 | GLOBAL_ENTRY(jprobe_inst_return) |
| 61 | br.call.sptk.many b0=jprobe_break |
| 62 | END(jprobe_inst_return) |