Commit | Line | Data |
---|---|---|
4e491d14 SR |
1 | /* |
2 | * Code for replacing ftrace calls with jumps. | |
3 | * | |
4 | * Copyright (C) 2007-2008 Steven Rostedt <srostedt@redhat.com> | |
5 | * | |
6 | * Thanks goes out to P.A. Semi, Inc for supplying me with a PPC64 box. | |
7 | * | |
8 | */ | |
9 | ||
10 | #include <linux/spinlock.h> | |
11 | #include <linux/hardirq.h> | |
e4486fe3 | 12 | #include <linux/uaccess.h> |
f48cb8b4 | 13 | #include <linux/module.h> |
4e491d14 SR |
14 | #include <linux/ftrace.h> |
15 | #include <linux/percpu.h> | |
16 | #include <linux/init.h> | |
17 | #include <linux/list.h> | |
18 | ||
19 | #include <asm/cacheflush.h> | |
f48cb8b4 | 20 | #include <asm/code-patching.h> |
395a59d0 | 21 | #include <asm/ftrace.h> |
4e491d14 | 22 | |
f48cb8b4 | 23 | static unsigned int ftrace_nop = PPC_NOP_INSTR; |
4e491d14 SR |
24 | |
25 | #ifdef CONFIG_PPC32 | |
26 | # define GET_ADDR(addr) addr | |
27 | #else | |
28 | /* PowerPC64's functions are data that points to the functions */ | |
f48cb8b4 | 29 | # define GET_ADDR(addr) (*(unsigned long *)addr) |
4e491d14 SR |
30 | #endif |
31 | ||
395a59d0 | 32 | |
15adc048 | 33 | static unsigned int ftrace_calc_offset(long ip, long addr) |
4e491d14 | 34 | { |
395a59d0 | 35 | return (int)(addr - ip); |
4e491d14 SR |
36 | } |
37 | ||
8fd6e5a8 | 38 | static unsigned char *ftrace_nop_replace(void) |
4e491d14 SR |
39 | { |
40 | return (char *)&ftrace_nop; | |
41 | } | |
42 | ||
8fd6e5a8 | 43 | static unsigned char *ftrace_call_replace(unsigned long ip, unsigned long addr) |
4e491d14 SR |
44 | { |
45 | static unsigned int op; | |
46 | ||
ccbfac29 SR |
47 | /* |
48 | * It would be nice to just use create_function_call, but that will | |
49 | * update the code itself. Here we need to just return the | |
50 | * instruction that is going to be modified, without modifying the | |
51 | * code. | |
52 | */ | |
4e491d14 SR |
53 | addr = GET_ADDR(addr); |
54 | ||
55 | /* Set to "bl addr" */ | |
ccbfac29 | 56 | op = 0x48000001 | (ftrace_calc_offset(ip, addr) & 0x03fffffc); |
4e491d14 SR |
57 | |
58 | /* | |
59 | * No locking needed, this must be called via kstop_machine | |
60 | * which in essence is like running on a uniprocessor machine. | |
61 | */ | |
62 | return (unsigned char *)&op; | |
63 | } | |
64 | ||
65 | #ifdef CONFIG_PPC64 | |
66 | # define _ASM_ALIGN " .align 3 " | |
67 | # define _ASM_PTR " .llong " | |
68 | #else | |
69 | # define _ASM_ALIGN " .align 2 " | |
70 | # define _ASM_PTR " .long " | |
71 | #endif | |
72 | ||
8fd6e5a8 | 73 | static int |
4e491d14 SR |
74 | ftrace_modify_code(unsigned long ip, unsigned char *old_code, |
75 | unsigned char *new_code) | |
76 | { | |
e4486fe3 | 77 | unsigned char replaced[MCOUNT_INSN_SIZE]; |
4e491d14 | 78 | |
4e491d14 SR |
79 | /* |
80 | * Note: Due to modules and __init, code can | |
81 | * disappear and change, we need to protect against faulting | |
e4486fe3 SR |
82 | * as well as code changing. We do this by using the |
83 | * probe_kernel_* functions. | |
4e491d14 SR |
84 | * |
85 | * No real locking needed, this code is run through | |
e4486fe3 | 86 | * kstop_machine, or before SMP starts. |
4e491d14 | 87 | */ |
e4486fe3 SR |
88 | |
89 | /* read the text we want to modify */ | |
90 | if (probe_kernel_read(replaced, (void *)ip, MCOUNT_INSN_SIZE)) | |
91 | return -EFAULT; | |
92 | ||
93 | /* Make sure it is what we expect it to be */ | |
94 | if (memcmp(replaced, old_code, MCOUNT_INSN_SIZE) != 0) | |
95 | return -EINVAL; | |
96 | ||
97 | /* replace the text with the new text */ | |
98 | if (probe_kernel_write((void *)ip, new_code, MCOUNT_INSN_SIZE)) | |
99 | return -EPERM; | |
100 | ||
101 | flush_icache_range(ip, ip + 8); | |
102 | ||
103 | return 0; | |
4e491d14 SR |
104 | } |
105 | ||
f48cb8b4 SR |
106 | /* |
107 | * Helper functions that are the same for both PPC64 and PPC32. | |
108 | */ | |
8fd6e5a8 SR |
109 | static int test_24bit_addr(unsigned long ip, unsigned long addr) |
110 | { | |
8fd6e5a8 | 111 | |
0029ff87 SR |
112 | /* use the create_branch to verify that this offset can be branched */ |
113 | return create_branch((unsigned int *)ip, addr, 0); | |
8fd6e5a8 SR |
114 | } |
115 | ||
f48cb8b4 SR |
116 | static int is_bl_op(unsigned int op) |
117 | { | |
118 | return (op & 0xfc000003) == 0x48000001; | |
119 | } | |
120 | ||
f48cb8b4 SR |
121 | static unsigned long find_bl_target(unsigned long ip, unsigned int op) |
122 | { | |
123 | static int offset; | |
124 | ||
125 | offset = (op & 0x03fffffc); | |
126 | /* make it signed */ | |
127 | if (offset & 0x02000000) | |
128 | offset |= 0xfe000000; | |
129 | ||
130 | return ip + (long)offset; | |
131 | } | |
132 | ||
f48cb8b4 SR |
133 | #ifdef CONFIG_PPC64 |
134 | static int | |
135 | __ftrace_make_nop(struct module *mod, | |
136 | struct dyn_ftrace *rec, unsigned long addr) | |
137 | { | |
d9af12b7 SR |
138 | unsigned int op; |
139 | unsigned int jmp[5]; | |
140 | unsigned long ptr; | |
f48cb8b4 SR |
141 | unsigned long ip = rec->ip; |
142 | unsigned long tramp; | |
143 | int offset; | |
144 | ||
145 | /* read where this goes */ | |
d9af12b7 | 146 | if (probe_kernel_read(&op, (void *)ip, sizeof(int))) |
f48cb8b4 SR |
147 | return -EFAULT; |
148 | ||
149 | /* Make sure that that this is still a 24bit jump */ | |
d9af12b7 SR |
150 | if (!is_bl_op(op)) { |
151 | printk(KERN_ERR "Not expected bl: opcode is %x\n", op); | |
f48cb8b4 SR |
152 | return -EINVAL; |
153 | } | |
154 | ||
155 | /* lets find where the pointer goes */ | |
d9af12b7 | 156 | tramp = find_bl_target(ip, op); |
f48cb8b4 SR |
157 | |
158 | /* | |
159 | * On PPC64 the trampoline looks like: | |
160 | * 0x3d, 0x82, 0x00, 0x00, addis r12,r2, <high> | |
161 | * 0x39, 0x8c, 0x00, 0x00, addi r12,r12, <low> | |
162 | * Where the bytes 2,3,6 and 7 make up the 32bit offset | |
163 | * to the TOC that holds the pointer. | |
164 | * to jump to. | |
165 | * 0xf8, 0x41, 0x00, 0x28, std r2,40(r1) | |
166 | * 0xe9, 0x6c, 0x00, 0x20, ld r11,32(r12) | |
167 | * The actually address is 32 bytes from the offset | |
168 | * into the TOC. | |
169 | * 0xe8, 0x4c, 0x00, 0x28, ld r2,40(r12) | |
170 | */ | |
171 | ||
44e1d064 | 172 | pr_debug("ip:%lx jumps to %lx r2: %lx", ip, tramp, mod->arch.toc); |
f48cb8b4 SR |
173 | |
174 | /* Find where the trampoline jumps to */ | |
d9af12b7 | 175 | if (probe_kernel_read(jmp, (void *)tramp, sizeof(jmp))) { |
f48cb8b4 SR |
176 | printk(KERN_ERR "Failed to read %lx\n", tramp); |
177 | return -EFAULT; | |
178 | } | |
179 | ||
44e1d064 | 180 | pr_debug(" %08x %08x", jmp[0], jmp[1]); |
d9af12b7 SR |
181 | |
182 | /* verify that this is what we expect it to be */ | |
183 | if (((jmp[0] & 0xffff0000) != 0x3d820000) || | |
184 | ((jmp[1] & 0xffff0000) != 0x398c0000) || | |
185 | (jmp[2] != 0xf8410028) || | |
186 | (jmp[3] != 0xe96c0020) || | |
187 | (jmp[4] != 0xe84c0028)) { | |
188 | printk(KERN_ERR "Not a trampoline\n"); | |
189 | return -EINVAL; | |
190 | } | |
f48cb8b4 | 191 | |
f25f9074 SR |
192 | /* The bottom half is signed extended */ |
193 | offset = ((unsigned)((unsigned short)jmp[0]) << 16) + | |
194 | (int)((short)jmp[1]); | |
f48cb8b4 | 195 | |
44e1d064 | 196 | pr_debug(" %x ", offset); |
f48cb8b4 SR |
197 | |
198 | /* get the address this jumps too */ | |
199 | tramp = mod->arch.toc + offset + 32; | |
44e1d064 | 200 | pr_debug("toc: %lx", tramp); |
f48cb8b4 SR |
201 | |
202 | if (probe_kernel_read(jmp, (void *)tramp, 8)) { | |
203 | printk(KERN_ERR "Failed to read %lx\n", tramp); | |
204 | return -EFAULT; | |
205 | } | |
206 | ||
44e1d064 | 207 | pr_debug(" %08x %08x\n", jmp[0], jmp[1]); |
d9af12b7 SR |
208 | |
209 | ptr = ((unsigned long)jmp[0] << 32) + jmp[1]; | |
f48cb8b4 SR |
210 | |
211 | /* This should match what was called */ | |
d9af12b7 SR |
212 | if (ptr != GET_ADDR(addr)) { |
213 | printk(KERN_ERR "addr does not match %lx\n", ptr); | |
f48cb8b4 SR |
214 | return -EINVAL; |
215 | } | |
216 | ||
217 | /* | |
218 | * We want to nop the line, but the next line is | |
219 | * 0xe8, 0x41, 0x00, 0x28 ld r2,40(r1) | |
220 | * This needs to be turned to a nop too. | |
221 | */ | |
d9af12b7 | 222 | if (probe_kernel_read(&op, (void *)(ip+4), MCOUNT_INSN_SIZE)) |
f48cb8b4 SR |
223 | return -EFAULT; |
224 | ||
d9af12b7 SR |
225 | if (op != 0xe8410028) { |
226 | printk(KERN_ERR "Next line is not ld! (%08x)\n", op); | |
f48cb8b4 SR |
227 | return -EINVAL; |
228 | } | |
229 | ||
230 | /* | |
231 | * Milton Miller pointed out that we can not blindly do nops. | |
232 | * If a task was preempted when calling a trace function, | |
233 | * the nops will remove the way to restore the TOC in r2 | |
234 | * and the r2 TOC will get corrupted. | |
235 | */ | |
236 | ||
237 | /* | |
238 | * Replace: | |
239 | * bl <tramp> <==== will be replaced with "b 1f" | |
240 | * ld r2,40(r1) | |
241 | * 1: | |
242 | */ | |
d9af12b7 | 243 | op = 0x48000008; /* b +8 */ |
f48cb8b4 | 244 | |
d9af12b7 | 245 | if (probe_kernel_write((void *)ip, &op, MCOUNT_INSN_SIZE)) |
f48cb8b4 SR |
246 | return -EPERM; |
247 | ||
ec682cef SR |
248 | |
249 | flush_icache_range(ip, ip + 8); | |
250 | ||
f48cb8b4 SR |
251 | return 0; |
252 | } | |
253 | ||
254 | #else /* !PPC64 */ | |
255 | static int | |
256 | __ftrace_make_nop(struct module *mod, | |
257 | struct dyn_ftrace *rec, unsigned long addr) | |
258 | { | |
d9af12b7 SR |
259 | unsigned int op; |
260 | unsigned int jmp[4]; | |
7cc45e64 SR |
261 | unsigned long ip = rec->ip; |
262 | unsigned long tramp; | |
7cc45e64 | 263 | |
d9af12b7 | 264 | if (probe_kernel_read(&op, (void *)ip, MCOUNT_INSN_SIZE)) |
7cc45e64 SR |
265 | return -EFAULT; |
266 | ||
267 | /* Make sure that that this is still a 24bit jump */ | |
d9af12b7 SR |
268 | if (!is_bl_op(op)) { |
269 | printk(KERN_ERR "Not expected bl: opcode is %x\n", op); | |
7cc45e64 SR |
270 | return -EINVAL; |
271 | } | |
272 | ||
273 | /* lets find where the pointer goes */ | |
d9af12b7 | 274 | tramp = find_bl_target(ip, op); |
7cc45e64 SR |
275 | |
276 | /* | |
277 | * On PPC32 the trampoline looks like: | |
d9af12b7 SR |
278 | * 0x3d, 0x60, 0x00, 0x00 lis r11,sym@ha |
279 | * 0x39, 0x6b, 0x00, 0x00 addi r11,r11,sym@l | |
280 | * 0x7d, 0x69, 0x03, 0xa6 mtctr r11 | |
281 | * 0x4e, 0x80, 0x04, 0x20 bctr | |
7cc45e64 SR |
282 | */ |
283 | ||
44e1d064 | 284 | pr_debug("ip:%lx jumps to %lx", ip, tramp); |
7cc45e64 SR |
285 | |
286 | /* Find where the trampoline jumps to */ | |
d9af12b7 | 287 | if (probe_kernel_read(jmp, (void *)tramp, sizeof(jmp))) { |
7cc45e64 SR |
288 | printk(KERN_ERR "Failed to read %lx\n", tramp); |
289 | return -EFAULT; | |
290 | } | |
291 | ||
44e1d064 | 292 | pr_debug(" %08x %08x ", jmp[0], jmp[1]); |
d9af12b7 SR |
293 | |
294 | /* verify that this is what we expect it to be */ | |
295 | if (((jmp[0] & 0xffff0000) != 0x3d600000) || | |
296 | ((jmp[1] & 0xffff0000) != 0x396b0000) || | |
297 | (jmp[2] != 0x7d6903a6) || | |
298 | (jmp[3] != 0x4e800420)) { | |
299 | printk(KERN_ERR "Not a trampoline\n"); | |
300 | return -EINVAL; | |
301 | } | |
7cc45e64 | 302 | |
d9af12b7 SR |
303 | tramp = (jmp[1] & 0xffff) | |
304 | ((jmp[0] & 0xffff) << 16); | |
7cc45e64 SR |
305 | if (tramp & 0x8000) |
306 | tramp -= 0x10000; | |
307 | ||
44e1d064 | 308 | pr_debug(" %x ", tramp); |
7cc45e64 SR |
309 | |
310 | if (tramp != addr) { | |
311 | printk(KERN_ERR | |
312 | "Trampoline location %08lx does not match addr\n", | |
313 | tramp); | |
314 | return -EINVAL; | |
315 | } | |
316 | ||
d9af12b7 | 317 | op = PPC_NOP_INSTR; |
7cc45e64 | 318 | |
d9af12b7 | 319 | if (probe_kernel_write((void *)ip, &op, MCOUNT_INSN_SIZE)) |
7cc45e64 SR |
320 | return -EPERM; |
321 | ||
ec682cef SR |
322 | flush_icache_range(ip, ip + 8); |
323 | ||
f48cb8b4 SR |
324 | return 0; |
325 | } | |
326 | #endif /* PPC64 */ | |
327 | ||
8fd6e5a8 SR |
328 | int ftrace_make_nop(struct module *mod, |
329 | struct dyn_ftrace *rec, unsigned long addr) | |
330 | { | |
331 | unsigned char *old, *new; | |
f48cb8b4 | 332 | unsigned long ip = rec->ip; |
8fd6e5a8 SR |
333 | |
334 | /* | |
335 | * If the calling address is more that 24 bits away, | |
336 | * then we had to use a trampoline to make the call. | |
337 | * Otherwise just update the call site. | |
338 | */ | |
f48cb8b4 | 339 | if (test_24bit_addr(ip, addr)) { |
8fd6e5a8 | 340 | /* within range */ |
f48cb8b4 | 341 | old = ftrace_call_replace(ip, addr); |
8fd6e5a8 | 342 | new = ftrace_nop_replace(); |
f48cb8b4 SR |
343 | return ftrace_modify_code(ip, old, new); |
344 | } | |
345 | ||
f48cb8b4 SR |
346 | /* |
347 | * Out of range jumps are called from modules. | |
348 | * We should either already have a pointer to the module | |
349 | * or it has been passed in. | |
350 | */ | |
351 | if (!rec->arch.mod) { | |
352 | if (!mod) { | |
353 | printk(KERN_ERR "No module loaded addr=%lx\n", | |
354 | addr); | |
355 | return -EFAULT; | |
356 | } | |
357 | rec->arch.mod = mod; | |
358 | } else if (mod) { | |
359 | if (mod != rec->arch.mod) { | |
360 | printk(KERN_ERR | |
361 | "Record mod %p not equal to passed in mod %p\n", | |
362 | rec->arch.mod, mod); | |
363 | return -EINVAL; | |
364 | } | |
365 | /* nothing to do if mod == rec->arch.mod */ | |
366 | } else | |
367 | mod = rec->arch.mod; | |
f48cb8b4 SR |
368 | |
369 | return __ftrace_make_nop(mod, rec, addr); | |
370 | ||
371 | } | |
372 | ||
373 | #ifdef CONFIG_PPC64 | |
374 | static int | |
375 | __ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr) | |
376 | { | |
d9af12b7 | 377 | unsigned int op[2]; |
f48cb8b4 | 378 | unsigned long ip = rec->ip; |
f48cb8b4 SR |
379 | |
380 | /* read where this goes */ | |
d9af12b7 | 381 | if (probe_kernel_read(op, (void *)ip, MCOUNT_INSN_SIZE * 2)) |
f48cb8b4 SR |
382 | return -EFAULT; |
383 | ||
384 | /* | |
385 | * It should be pointing to two nops or | |
386 | * b +8; ld r2,40(r1) | |
387 | */ | |
388 | if (((op[0] != 0x48000008) || (op[1] != 0xe8410028)) && | |
389 | ((op[0] != PPC_NOP_INSTR) || (op[1] != PPC_NOP_INSTR))) { | |
390 | printk(KERN_ERR "Expected NOPs but have %x %x\n", op[0], op[1]); | |
391 | return -EINVAL; | |
392 | } | |
393 | ||
394 | /* If we never set up a trampoline to ftrace_caller, then bail */ | |
395 | if (!rec->arch.mod->arch.tramp) { | |
396 | printk(KERN_ERR "No ftrace trampoline\n"); | |
397 | return -EINVAL; | |
398 | } | |
399 | ||
0029ff87 SR |
400 | /* create the branch to the trampoline */ |
401 | op[0] = create_branch((unsigned int *)ip, | |
402 | rec->arch.mod->arch.tramp, BRANCH_SET_LINK); | |
403 | if (!op[0]) { | |
404 | printk(KERN_ERR "REL24 out of range!\n"); | |
f48cb8b4 | 405 | return -EINVAL; |
8fd6e5a8 SR |
406 | } |
407 | ||
f48cb8b4 SR |
408 | /* ld r2,40(r1) */ |
409 | op[1] = 0xe8410028; | |
410 | ||
44e1d064 | 411 | pr_debug("write to %lx\n", rec->ip); |
f48cb8b4 | 412 | |
d9af12b7 | 413 | if (probe_kernel_write((void *)ip, op, MCOUNT_INSN_SIZE * 2)) |
f48cb8b4 SR |
414 | return -EPERM; |
415 | ||
ec682cef SR |
416 | flush_icache_range(ip, ip + 8); |
417 | ||
8fd6e5a8 SR |
418 | return 0; |
419 | } | |
f48cb8b4 SR |
420 | #else |
421 | static int | |
422 | __ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr) | |
423 | { | |
d9af12b7 | 424 | unsigned int op; |
7cc45e64 | 425 | unsigned long ip = rec->ip; |
7cc45e64 SR |
426 | |
427 | /* read where this goes */ | |
d9af12b7 | 428 | if (probe_kernel_read(&op, (void *)ip, MCOUNT_INSN_SIZE)) |
7cc45e64 SR |
429 | return -EFAULT; |
430 | ||
431 | /* It should be pointing to a nop */ | |
d9af12b7 SR |
432 | if (op != PPC_NOP_INSTR) { |
433 | printk(KERN_ERR "Expected NOP but have %x\n", op); | |
7cc45e64 SR |
434 | return -EINVAL; |
435 | } | |
436 | ||
437 | /* If we never set up a trampoline to ftrace_caller, then bail */ | |
438 | if (!rec->arch.mod->arch.tramp) { | |
439 | printk(KERN_ERR "No ftrace trampoline\n"); | |
440 | return -EINVAL; | |
441 | } | |
442 | ||
0029ff87 SR |
443 | /* create the branch to the trampoline */ |
444 | op = create_branch((unsigned int *)ip, | |
445 | rec->arch.mod->arch.tramp, BRANCH_SET_LINK); | |
446 | if (!op) { | |
447 | printk(KERN_ERR "REL24 out of range!\n"); | |
7cc45e64 SR |
448 | return -EINVAL; |
449 | } | |
450 | ||
44e1d064 | 451 | pr_debug("write to %lx\n", rec->ip); |
7cc45e64 | 452 | |
d9af12b7 | 453 | if (probe_kernel_write((void *)ip, &op, MCOUNT_INSN_SIZE)) |
7cc45e64 SR |
454 | return -EPERM; |
455 | ||
ec682cef SR |
456 | flush_icache_range(ip, ip + 8); |
457 | ||
f48cb8b4 SR |
458 | return 0; |
459 | } | |
460 | #endif /* CONFIG_PPC64 */ | |
8fd6e5a8 SR |
461 | |
462 | int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr) | |
463 | { | |
464 | unsigned char *old, *new; | |
f48cb8b4 | 465 | unsigned long ip = rec->ip; |
8fd6e5a8 SR |
466 | |
467 | /* | |
468 | * If the calling address is more that 24 bits away, | |
469 | * then we had to use a trampoline to make the call. | |
470 | * Otherwise just update the call site. | |
471 | */ | |
f48cb8b4 | 472 | if (test_24bit_addr(ip, addr)) { |
8fd6e5a8 SR |
473 | /* within range */ |
474 | old = ftrace_nop_replace(); | |
f48cb8b4 SR |
475 | new = ftrace_call_replace(ip, addr); |
476 | return ftrace_modify_code(ip, old, new); | |
8fd6e5a8 SR |
477 | } |
478 | ||
f48cb8b4 SR |
479 | /* |
480 | * Out of range jumps are called from modules. | |
481 | * Being that we are converting from nop, it had better | |
482 | * already have a module defined. | |
483 | */ | |
484 | if (!rec->arch.mod) { | |
485 | printk(KERN_ERR "No module loaded\n"); | |
486 | return -EINVAL; | |
487 | } | |
f48cb8b4 SR |
488 | |
489 | return __ftrace_make_call(rec, addr); | |
8fd6e5a8 SR |
490 | } |
491 | ||
15adc048 | 492 | int ftrace_update_ftrace_func(ftrace_func_t func) |
4e491d14 SR |
493 | { |
494 | unsigned long ip = (unsigned long)(&ftrace_call); | |
395a59d0 | 495 | unsigned char old[MCOUNT_INSN_SIZE], *new; |
4e491d14 SR |
496 | int ret; |
497 | ||
395a59d0 | 498 | memcpy(old, &ftrace_call, MCOUNT_INSN_SIZE); |
4e491d14 SR |
499 | new = ftrace_call_replace(ip, (unsigned long)func); |
500 | ret = ftrace_modify_code(ip, old, new); | |
501 | ||
502 | return ret; | |
503 | } | |
504 | ||
4e491d14 SR |
505 | int __init ftrace_dyn_arch_init(void *data) |
506 | { | |
8fd6e5a8 SR |
507 | /* caller expects data to be zero */ |
508 | unsigned long *p = data; | |
4e491d14 | 509 | |
8fd6e5a8 | 510 | *p = 0; |
4e491d14 SR |
511 | |
512 | return 0; | |
513 | } |