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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 | */ | |
52 | ENTRY(jprobe_break) | |
53 | break.m 0x80300 | |
54 | END(jprobe_break) | |
55 | ||
56 | /* | |
57 | * void jprobe_inst_return(void) | |
58 | */ | |
59 | GLOBAL_ENTRY(jprobe_inst_return) | |
60 | br.call.sptk.many b0=jprobe_break | |
61 | END(jprobe_inst_return) |