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).
7 * Restructured to fit Linux format, as well as other updates:
8 * Copyright 2010 Steven Rostedt <srostedt@redhat.com>, Red Hat Inc.
12 * Strategy: alter the .o file in-place.
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.]
24 #include <sys/types.h>
35 static int fd_map; /* File descriptor for file being modified. */
36 static int mmap_failed; /* Boolean flag. */
37 static void *ehdr_curr; /* current ElfXX_Ehdr * for resource cleanup */
38 static char gpfx; /* prefix for global symbol name (sometimes '_') */
39 static struct stat sb; /* Remember .st_size, etc. */
40 static jmp_buf jmpenv; /* setjmp/longjmp per-file error escape */
41 static const char *altmcount; /* alternate mcount symbol name */
43 /* setjmp() return values */
45 SJ_SETJMP = 0, /* hardwired first return */
50 /* Per-file resource cleanup when multiple files. */
55 munmap(ehdr_curr, sb.st_size);
61 static void __attribute__((noreturn))
65 longjmp(jmpenv, SJ_FAIL);
68 static void __attribute__((noreturn))
72 longjmp(jmpenv, SJ_SUCCEED);
75 /* ulseek, uread, ...: Check return value for errors. */
78 ulseek(int const fd, off_t const offset, int const whence)
80 off_t const w = lseek(fd, offset, whence);
89 uread(int const fd, void *const buf, size_t const count)
91 size_t const n = read(fd, buf, count);
100 uwrite(int const fd, void const *const buf, size_t const count)
102 size_t const n = write(fd, buf, count);
113 void *const addr = malloc(size);
115 fprintf(stderr, "malloc failed: %zu bytes\n", size);
121 static unsigned char ideal_nop5_x86_64[5] = { 0x0f, 0x1f, 0x44, 0x00, 0x00 };
122 static unsigned char ideal_nop5_x86_32[5] = { 0x3e, 0x8d, 0x74, 0x26, 0x00 };
123 static unsigned char *ideal_nop;
125 static char rel_type_nop;
127 static int (*make_nop)(void *map, size_t const offset);
129 static int make_nop_x86(void *map, size_t const offset)
134 /* Confirm we have 0xe8 0x0 0x0 0x0 0x0 */
139 op = map + offset - 1;
144 ulseek(fd_map, offset - 1, SEEK_SET);
145 uwrite(fd_map, ideal_nop, 5);
150 * Get the whole file as a programming convenience in order to avoid
151 * malloc+lseek+read+free of many pieces. If successful, then mmap
152 * avoids copying unused pieces; else just read the whole file.
153 * Open for both read and write; new info will be appended to the file.
154 * Use MAP_PRIVATE so that a few changes to the in-memory ElfXX_Ehdr
155 * do not propagate to the file until an explicit overwrite at the last.
156 * This preserves most aspects of consistency (all except .st_size)
157 * for simultaneous readers of the file while we are appending to it.
158 * However, multiple writers still are bad. We choose not to use
159 * locking because it is expensive and the use case of kernel build
160 * makes multiple writers unlikely.
162 static void *mmap_file(char const *fname)
166 fd_map = open(fname, O_RDWR);
167 if (fd_map < 0 || fstat(fd_map, &sb) < 0) {
171 if (!S_ISREG(sb.st_mode)) {
172 fprintf(stderr, "not a regular file: %s\n", fname);
175 addr = mmap(0, sb.st_size, PROT_READ|PROT_WRITE, MAP_PRIVATE,
178 if (addr == MAP_FAILED) {
180 addr = umalloc(sb.st_size);
181 uread(fd_map, addr, sb.st_size);
186 /* w8rev, w8nat, ...: Handle endianness. */
188 static uint64_t w8rev(uint64_t const x)
190 return ((0xff & (x >> (0 * 8))) << (7 * 8))
191 | ((0xff & (x >> (1 * 8))) << (6 * 8))
192 | ((0xff & (x >> (2 * 8))) << (5 * 8))
193 | ((0xff & (x >> (3 * 8))) << (4 * 8))
194 | ((0xff & (x >> (4 * 8))) << (3 * 8))
195 | ((0xff & (x >> (5 * 8))) << (2 * 8))
196 | ((0xff & (x >> (6 * 8))) << (1 * 8))
197 | ((0xff & (x >> (7 * 8))) << (0 * 8));
200 static uint32_t w4rev(uint32_t const x)
202 return ((0xff & (x >> (0 * 8))) << (3 * 8))
203 | ((0xff & (x >> (1 * 8))) << (2 * 8))
204 | ((0xff & (x >> (2 * 8))) << (1 * 8))
205 | ((0xff & (x >> (3 * 8))) << (0 * 8));
208 static uint32_t w2rev(uint16_t const x)
210 return ((0xff & (x >> (0 * 8))) << (1 * 8))
211 | ((0xff & (x >> (1 * 8))) << (0 * 8));
214 static uint64_t w8nat(uint64_t const x)
219 static uint32_t w4nat(uint32_t const x)
224 static uint32_t w2nat(uint16_t const x)
229 static uint64_t (*w8)(uint64_t);
230 static uint32_t (*w)(uint32_t);
231 static uint32_t (*w2)(uint16_t);
233 /* Names of the sections that could contain calls to mcount. */
235 is_mcounted_section_name(char const *const txtname)
237 return strcmp(".text", txtname) == 0 ||
238 strcmp(".ref.text", txtname) == 0 ||
239 strcmp(".sched.text", txtname) == 0 ||
240 strcmp(".spinlock.text", txtname) == 0 ||
241 strcmp(".irqentry.text", txtname) == 0 ||
242 strcmp(".kprobes.text", txtname) == 0 ||
243 strcmp(".text.unlikely", txtname) == 0;
246 /* 32 bit and 64 bit are very similar */
247 #include "recordmcount.h"
248 #define RECORD_MCOUNT_64
249 #include "recordmcount.h"
251 /* 64-bit EM_MIPS has weird ELF64_Rela.r_info.
252 * http://techpubs.sgi.com/library/manuals/4000/007-4658-001/pdf/007-4658-001.pdf
253 * We interpret Table 29 Relocation Operation (Elf64_Rel, Elf64_Rela) [p.40]
254 * to imply the order of the members; the spec does not say so.
255 * typedef unsigned char Elf64_Byte;
256 * fails on MIPS64 because their <elf.h> already has it!
259 typedef uint8_t myElf64_Byte; /* Type for a 8-bit quantity. */
264 Elf64_Word r_sym; /* Symbol index. */
265 myElf64_Byte r_ssym; /* Special symbol. */
266 myElf64_Byte r_type3; /* Third relocation. */
267 myElf64_Byte r_type2; /* Second relocation. */
268 myElf64_Byte r_type; /* First relocation. */
272 static uint64_t MIPS64_r_sym(Elf64_Rel const *rp)
274 return w(((union mips_r_info){ .r_info = rp->r_info }).r_mips.r_sym);
277 static void MIPS64_r_info(Elf64_Rel *const rp, unsigned sym, unsigned type)
279 rp->r_info = ((union mips_r_info){
280 .r_mips = { .r_sym = w(sym), .r_type = type }
285 do_file(char const *const fname)
287 Elf32_Ehdr *const ehdr = mmap_file(fname);
288 unsigned int reltype = 0;
294 switch (ehdr->e_ident[EI_DATA]) {
295 static unsigned int const endian = 1;
297 fprintf(stderr, "unrecognized ELF data encoding %d: %s\n",
298 ehdr->e_ident[EI_DATA], fname);
302 if (*(unsigned char const *)&endian != 1) {
303 /* main() is big endian, file.o is little endian. */
310 if (*(unsigned char const *)&endian != 0) {
311 /* main() is little endian, file.o is big endian. */
318 if (memcmp(ELFMAG, ehdr->e_ident, SELFMAG) != 0
319 || w2(ehdr->e_type) != ET_REL
320 || ehdr->e_ident[EI_VERSION] != EV_CURRENT) {
321 fprintf(stderr, "unrecognized ET_REL file %s\n", fname);
326 switch (w2(ehdr->e_machine)) {
328 fprintf(stderr, "unrecognized e_machine %d %s\n",
329 w2(ehdr->e_machine), fname);
334 make_nop = make_nop_x86;
335 ideal_nop = ideal_nop5_x86_32;
337 case EM_ARM: reltype = R_ARM_ABS32;
338 altmcount = "__gnu_mcount_nc";
340 case EM_IA_64: reltype = R_IA64_IMM64; gpfx = '_'; break;
341 case EM_MIPS: /* reltype: e_class */ gpfx = '_'; break;
342 case EM_PPC: reltype = R_PPC_ADDR32; gpfx = '_'; break;
343 case EM_PPC64: reltype = R_PPC64_ADDR64; gpfx = '_'; break;
344 case EM_S390: /* reltype: e_class */ gpfx = '_'; break;
345 case EM_SH: reltype = R_SH_DIR32; break;
346 case EM_SPARCV9: reltype = R_SPARC_64; gpfx = '_'; break;
348 make_nop = make_nop_x86;
349 ideal_nop = ideal_nop5_x86_64;
350 reltype = R_X86_64_64;
354 switch (ehdr->e_ident[EI_CLASS]) {
356 fprintf(stderr, "unrecognized ELF class %d %s\n",
357 ehdr->e_ident[EI_CLASS], fname);
361 if (w2(ehdr->e_ehsize) != sizeof(Elf32_Ehdr)
362 || w2(ehdr->e_shentsize) != sizeof(Elf32_Shdr)) {
364 "unrecognized ET_REL file: %s\n", fname);
367 if (w2(ehdr->e_machine) == EM_S390)
369 if (w2(ehdr->e_machine) == EM_MIPS) {
371 is_fake_mcount32 = MIPS32_is_fake_mcount;
373 do32(ehdr, fname, reltype);
376 Elf64_Ehdr *const ghdr = (Elf64_Ehdr *)ehdr;
377 if (w2(ghdr->e_ehsize) != sizeof(Elf64_Ehdr)
378 || w2(ghdr->e_shentsize) != sizeof(Elf64_Shdr)) {
380 "unrecognized ET_REL file: %s\n", fname);
383 if (w2(ghdr->e_machine) == EM_S390)
385 if (w2(ghdr->e_machine) == EM_MIPS) {
387 Elf64_r_sym = MIPS64_r_sym;
388 Elf64_r_info = MIPS64_r_info;
389 is_fake_mcount64 = MIPS64_is_fake_mcount;
391 do64(ghdr, fname, reltype);
400 main(int argc, char const *argv[])
402 const char ftrace[] = "/ftrace.o";
403 int ftrace_size = sizeof(ftrace) - 1;
404 int n_error = 0; /* gcc-4.3.0 false positive complaint */
407 fprintf(stderr, "usage: recordmcount file.o...\n");
411 /* Process each file in turn, allowing deep failure. */
412 for (--argc, ++argv; argc > 0; --argc, ++argv) {
413 int const sjval = setjmp(jmpenv);
417 * The file kernel/trace/ftrace.o references the mcount
418 * function but does not call it. Since ftrace.o should
419 * not be traced anyway, we just skip it.
421 len = strlen(argv[0]);
422 if (len >= ftrace_size &&
423 strcmp(argv[0] + (len - ftrace_size), ftrace) == 0)
428 fprintf(stderr, "internal error: %s\n", argv[0]);
431 case SJ_SETJMP: /* normal sequence */
432 /* Avoid problems if early cleanup() */
438 case SJ_FAIL: /* error in do_file or below */
441 case SJ_SUCCEED: /* premature success */