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John Reiser81d38582010-10-13 15:12:54 -04001/*
2 * recordmcount.c: construct a table of the locations of calls to 'mcount'
3 * so that ftrace can find them quickly.
4 * Copyright 2009 John F. Reiser <jreiser@BitWagon.com>. All rights reserved.
5 * Licensed under the GNU General Public License, version 2 (GPLv2).
6 *
7 * Restructured to fit Linux format, as well as other updates:
8 * Copyright 2010 Steven Rostedt <srostedt@redhat.com>, Red Hat Inc.
9 */
10
11/*
12 * Strategy: alter the .o file in-place.
13 *
14 * Append a new STRTAB that has the new section names, followed by a new array
15 * ElfXX_Shdr[] that has the new section headers, followed by the section
16 * contents for __mcount_loc and its relocations. The old shstrtab strings,
17 * and the old ElfXX_Shdr[] array, remain as "garbage" (commonly, a couple
18 * kilobytes.) Subsequent processing by /bin/ld (or the kernel module loader)
19 * will ignore the garbage regions, because they are not designated by the
20 * new .e_shoff nor the new ElfXX_Shdr[]. [In order to remove the garbage,
21 * then use "ld -r" to create a new file that omits the garbage.]
22 */
23
24#include <sys/types.h>
25#include <sys/mman.h>
26#include <sys/stat.h>
27#include <elf.h>
28#include <fcntl.h>
29#include <setjmp.h>
30#include <stdio.h>
31#include <stdlib.h>
32#include <string.h>
33#include <unistd.h>
34
35static int fd_map; /* File descriptor for file being modified. */
36static int mmap_failed; /* Boolean flag. */
37static void *ehdr_curr; /* current ElfXX_Ehdr * for resource cleanup */
38static char gpfx; /* prefix for global symbol name (sometimes '_') */
39static struct stat sb; /* Remember .st_size, etc. */
40static jmp_buf jmpenv; /* setjmp/longjmp per-file error escape */
Rabin Vincented604532010-11-30 17:36:48 +010041static const char *altmcount; /* alternate mcount symbol name */
John Reiser81d38582010-10-13 15:12:54 -040042
43/* setjmp() return values */
44enum {
45 SJ_SETJMP = 0, /* hardwired first return */
46 SJ_FAIL,
47 SJ_SUCCEED
48};
49
50/* Per-file resource cleanup when multiple files. */
51static void
52cleanup(void)
53{
54 if (!mmap_failed)
55 munmap(ehdr_curr, sb.st_size);
56 else
57 free(ehdr_curr);
58 close(fd_map);
59}
60
61static void __attribute__((noreturn))
62fail_file(void)
63{
64 cleanup();
65 longjmp(jmpenv, SJ_FAIL);
66}
67
68static void __attribute__((noreturn))
69succeed_file(void)
70{
71 cleanup();
72 longjmp(jmpenv, SJ_SUCCEED);
73}
74
75/* ulseek, uread, ...: Check return value for errors. */
76
77static off_t
78ulseek(int const fd, off_t const offset, int const whence)
79{
80 off_t const w = lseek(fd, offset, whence);
81 if ((off_t)-1 == w) {
82 perror("lseek");
83 fail_file();
84 }
85 return w;
86}
87
88static size_t
89uread(int const fd, void *const buf, size_t const count)
90{
91 size_t const n = read(fd, buf, count);
92 if (n != count) {
93 perror("read");
94 fail_file();
95 }
96 return n;
97}
98
99static size_t
100uwrite(int const fd, void const *const buf, size_t const count)
101{
102 size_t const n = write(fd, buf, count);
103 if (n != count) {
104 perror("write");
105 fail_file();
106 }
107 return n;
108}
109
110static void *
111umalloc(size_t size)
112{
113 void *const addr = malloc(size);
114 if (0 == addr) {
115 fprintf(stderr, "malloc failed: %zu bytes\n", size);
116 fail_file();
117 }
118 return addr;
119}
120
121/*
122 * Get the whole file as a programming convenience in order to avoid
123 * malloc+lseek+read+free of many pieces. If successful, then mmap
124 * avoids copying unused pieces; else just read the whole file.
125 * Open for both read and write; new info will be appended to the file.
126 * Use MAP_PRIVATE so that a few changes to the in-memory ElfXX_Ehdr
127 * do not propagate to the file until an explicit overwrite at the last.
128 * This preserves most aspects of consistency (all except .st_size)
129 * for simultaneous readers of the file while we are appending to it.
130 * However, multiple writers still are bad. We choose not to use
131 * locking because it is expensive and the use case of kernel build
132 * makes multiple writers unlikely.
133 */
134static void *mmap_file(char const *fname)
135{
136 void *addr;
137
138 fd_map = open(fname, O_RDWR);
139 if (0 > fd_map || 0 > fstat(fd_map, &sb)) {
140 perror(fname);
141 fail_file();
142 }
143 if (!S_ISREG(sb.st_mode)) {
144 fprintf(stderr, "not a regular file: %s\n", fname);
145 fail_file();
146 }
147 addr = mmap(0, sb.st_size, PROT_READ|PROT_WRITE, MAP_PRIVATE,
148 fd_map, 0);
149 mmap_failed = 0;
150 if (MAP_FAILED == addr) {
151 mmap_failed = 1;
152 addr = umalloc(sb.st_size);
153 uread(fd_map, addr, sb.st_size);
154 }
155 return addr;
156}
157
158/* w8rev, w8nat, ...: Handle endianness. */
159
160static uint64_t w8rev(uint64_t const x)
161{
162 return ((0xff & (x >> (0 * 8))) << (7 * 8))
163 | ((0xff & (x >> (1 * 8))) << (6 * 8))
164 | ((0xff & (x >> (2 * 8))) << (5 * 8))
165 | ((0xff & (x >> (3 * 8))) << (4 * 8))
166 | ((0xff & (x >> (4 * 8))) << (3 * 8))
167 | ((0xff & (x >> (5 * 8))) << (2 * 8))
168 | ((0xff & (x >> (6 * 8))) << (1 * 8))
169 | ((0xff & (x >> (7 * 8))) << (0 * 8));
170}
171
172static uint32_t w4rev(uint32_t const x)
173{
174 return ((0xff & (x >> (0 * 8))) << (3 * 8))
175 | ((0xff & (x >> (1 * 8))) << (2 * 8))
176 | ((0xff & (x >> (2 * 8))) << (1 * 8))
177 | ((0xff & (x >> (3 * 8))) << (0 * 8));
178}
179
180static uint32_t w2rev(uint16_t const x)
181{
182 return ((0xff & (x >> (0 * 8))) << (1 * 8))
183 | ((0xff & (x >> (1 * 8))) << (0 * 8));
184}
185
186static uint64_t w8nat(uint64_t const x)
187{
188 return x;
189}
190
191static uint32_t w4nat(uint32_t const x)
192{
193 return x;
194}
195
196static uint32_t w2nat(uint16_t const x)
197{
198 return x;
199}
200
201static uint64_t (*w8)(uint64_t);
202static uint32_t (*w)(uint32_t);
203static uint32_t (*w2)(uint16_t);
204
205/* Names of the sections that could contain calls to mcount. */
206static int
207is_mcounted_section_name(char const *const txtname)
208{
Steven Rostedt1274a9c2011-02-11 16:43:33 -0500209 return 0 == strcmp(".text", txtname) ||
210 0 == strcmp(".ref.text", txtname) ||
John Reiser81d38582010-10-13 15:12:54 -0400211 0 == strcmp(".sched.text", txtname) ||
212 0 == strcmp(".spinlock.text", txtname) ||
213 0 == strcmp(".irqentry.text", txtname) ||
214 0 == strcmp(".text.unlikely", txtname);
215}
216
Steven Rostedtc28d5072010-10-13 19:06:14 -0400217/* 32 bit and 64 bit are very similar */
218#include "recordmcount.h"
219#define RECORD_MCOUNT_64
220#include "recordmcount.h"
John Reiser81d38582010-10-13 15:12:54 -0400221
John Reisera2d49352010-10-27 18:59:07 +0800222/* 64-bit EM_MIPS has weird ELF64_Rela.r_info.
223 * http://techpubs.sgi.com/library/manuals/4000/007-4658-001/pdf/007-4658-001.pdf
224 * We interpret Table 29 Relocation Operation (Elf64_Rel, Elf64_Rela) [p.40]
225 * to imply the order of the members; the spec does not say so.
226 * typedef unsigned char Elf64_Byte;
227 * fails on MIPS64 because their <elf.h> already has it!
228 */
229
230typedef uint8_t myElf64_Byte; /* Type for a 8-bit quantity. */
231
232union mips_r_info {
233 Elf64_Xword r_info;
234 struct {
235 Elf64_Word r_sym; /* Symbol index. */
236 myElf64_Byte r_ssym; /* Special symbol. */
237 myElf64_Byte r_type3; /* Third relocation. */
238 myElf64_Byte r_type2; /* Second relocation. */
239 myElf64_Byte r_type; /* First relocation. */
240 } r_mips;
241};
242
243static uint64_t MIPS64_r_sym(Elf64_Rel const *rp)
244{
245 return w(((union mips_r_info){ .r_info = rp->r_info }).r_mips.r_sym);
246}
247
248static void MIPS64_r_info(Elf64_Rel *const rp, unsigned sym, unsigned type)
249{
250 rp->r_info = ((union mips_r_info){
251 .r_mips = { .r_sym = w(sym), .r_type = type }
252 }).r_info;
253}
254
John Reiser81d38582010-10-13 15:12:54 -0400255static void
256do_file(char const *const fname)
257{
258 Elf32_Ehdr *const ehdr = mmap_file(fname);
259 unsigned int reltype = 0;
260
261 ehdr_curr = ehdr;
262 w = w4nat;
263 w2 = w2nat;
264 w8 = w8nat;
265 switch (ehdr->e_ident[EI_DATA]) {
266 static unsigned int const endian = 1;
267 default: {
268 fprintf(stderr, "unrecognized ELF data encoding %d: %s\n",
269 ehdr->e_ident[EI_DATA], fname);
270 fail_file();
271 } break;
272 case ELFDATA2LSB: {
273 if (1 != *(unsigned char const *)&endian) {
274 /* main() is big endian, file.o is little endian. */
275 w = w4rev;
276 w2 = w2rev;
277 w8 = w8rev;
278 }
279 } break;
280 case ELFDATA2MSB: {
281 if (0 != *(unsigned char const *)&endian) {
282 /* main() is little endian, file.o is big endian. */
283 w = w4rev;
284 w2 = w2rev;
285 w8 = w8rev;
286 }
287 } break;
288 } /* end switch */
289 if (0 != memcmp(ELFMAG, ehdr->e_ident, SELFMAG)
290 || ET_REL != w2(ehdr->e_type)
291 || EV_CURRENT != ehdr->e_ident[EI_VERSION]) {
292 fprintf(stderr, "unrecognized ET_REL file %s\n", fname);
293 fail_file();
294 }
295
296 gpfx = 0;
297 switch (w2(ehdr->e_machine)) {
298 default: {
299 fprintf(stderr, "unrecognized e_machine %d %s\n",
300 w2(ehdr->e_machine), fname);
301 fail_file();
302 } break;
303 case EM_386: reltype = R_386_32; break;
Rabin Vincented604532010-11-30 17:36:48 +0100304 case EM_ARM: reltype = R_ARM_ABS32;
305 altmcount = "__gnu_mcount_nc";
306 break;
John Reiser81d38582010-10-13 15:12:54 -0400307 case EM_IA_64: reltype = R_IA64_IMM64; gpfx = '_'; break;
John Reisera2d49352010-10-27 18:59:07 +0800308 case EM_MIPS: /* reltype: e_class */ gpfx = '_'; break;
John Reiser81d38582010-10-13 15:12:54 -0400309 case EM_PPC: reltype = R_PPC_ADDR32; gpfx = '_'; break;
310 case EM_PPC64: reltype = R_PPC64_ADDR64; gpfx = '_'; break;
311 case EM_S390: /* reltype: e_class */ gpfx = '_'; break;
312 case EM_SH: reltype = R_SH_DIR32; break;
313 case EM_SPARCV9: reltype = R_SPARC_64; gpfx = '_'; break;
314 case EM_X86_64: reltype = R_X86_64_64; break;
315 } /* end switch */
316
317 switch (ehdr->e_ident[EI_CLASS]) {
318 default: {
319 fprintf(stderr, "unrecognized ELF class %d %s\n",
320 ehdr->e_ident[EI_CLASS], fname);
321 fail_file();
322 } break;
323 case ELFCLASS32: {
324 if (sizeof(Elf32_Ehdr) != w2(ehdr->e_ehsize)
325 || sizeof(Elf32_Shdr) != w2(ehdr->e_shentsize)) {
326 fprintf(stderr,
327 "unrecognized ET_REL file: %s\n", fname);
328 fail_file();
329 }
330 if (EM_S390 == w2(ehdr->e_machine))
331 reltype = R_390_32;
Wu Zhangjin412910c2010-10-27 18:59:08 +0800332 if (EM_MIPS == w2(ehdr->e_machine)) {
John Reisera2d49352010-10-27 18:59:07 +0800333 reltype = R_MIPS_32;
Wu Zhangjin412910c2010-10-27 18:59:08 +0800334 is_fake_mcount32 = MIPS32_is_fake_mcount;
335 }
John Reiser81d38582010-10-13 15:12:54 -0400336 do32(ehdr, fname, reltype);
337 } break;
338 case ELFCLASS64: {
339 Elf64_Ehdr *const ghdr = (Elf64_Ehdr *)ehdr;
340 if (sizeof(Elf64_Ehdr) != w2(ghdr->e_ehsize)
341 || sizeof(Elf64_Shdr) != w2(ghdr->e_shentsize)) {
342 fprintf(stderr,
343 "unrecognized ET_REL file: %s\n", fname);
344 fail_file();
345 }
346 if (EM_S390 == w2(ghdr->e_machine))
347 reltype = R_390_64;
John Reisera2d49352010-10-27 18:59:07 +0800348 if (EM_MIPS == w2(ghdr->e_machine)) {
349 reltype = R_MIPS_64;
350 Elf64_r_sym = MIPS64_r_sym;
351 Elf64_r_info = MIPS64_r_info;
Wu Zhangjin412910c2010-10-27 18:59:08 +0800352 is_fake_mcount64 = MIPS64_is_fake_mcount;
John Reisera2d49352010-10-27 18:59:07 +0800353 }
John Reiser81d38582010-10-13 15:12:54 -0400354 do64(ghdr, fname, reltype);
355 } break;
356 } /* end switch */
357
358 cleanup();
359}
360
361int
362main(int argc, char const *argv[])
363{
Rabin Vincentcd3478f2010-11-30 17:33:53 +0100364 const char ftrace[] = "/ftrace.o";
Steven Rostedt44475862010-10-15 11:49:47 -0400365 int ftrace_size = sizeof(ftrace) - 1;
John Reiser81d38582010-10-13 15:12:54 -0400366 int n_error = 0; /* gcc-4.3.0 false positive complaint */
Steven Rostedt44475862010-10-15 11:49:47 -0400367
368 if (argc <= 1) {
John Reiser81d38582010-10-13 15:12:54 -0400369 fprintf(stderr, "usage: recordmcount file.o...\n");
Steven Rostedt44475862010-10-15 11:49:47 -0400370 return 0;
371 }
372
373 /* Process each file in turn, allowing deep failure. */
John Reiser81d38582010-10-13 15:12:54 -0400374 for (--argc, ++argv; 0 < argc; --argc, ++argv) {
375 int const sjval = setjmp(jmpenv);
Steven Rostedt44475862010-10-15 11:49:47 -0400376 int len;
377
378 /*
379 * The file kernel/trace/ftrace.o references the mcount
380 * function but does not call it. Since ftrace.o should
381 * not be traced anyway, we just skip it.
382 */
383 len = strlen(argv[0]);
384 if (len >= ftrace_size &&
385 strcmp(argv[0] + (len - ftrace_size), ftrace) == 0)
386 continue;
387
John Reiser81d38582010-10-13 15:12:54 -0400388 switch (sjval) {
389 default: {
390 fprintf(stderr, "internal error: %s\n", argv[0]);
391 exit(1);
392 } break;
393 case SJ_SETJMP: { /* normal sequence */
394 /* Avoid problems if early cleanup() */
395 fd_map = -1;
396 ehdr_curr = NULL;
397 mmap_failed = 1;
398 do_file(argv[0]);
399 } break;
400 case SJ_FAIL: { /* error in do_file or below */
401 ++n_error;
402 } break;
403 case SJ_SUCCEED: { /* premature success */
404 /* do nothing */
405 } break;
406 } /* end switch */
407 }
408 return !!n_error;
409}
410
411