recordmcount.c 12.4 KB
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484
/*
 * recordmcount.c: construct a table of the locations of calls to 'mcount'
 * so that ftrace can find them quickly.
 * Copyright 2009 John F. Reiser <jreiser@BitWagon.com>.  All rights reserved.
 * Licensed under the GNU General Public License, version 2 (GPLv2).
 *
 * Restructured to fit Linux format, as well as other updates:
 *  Copyright 2010 Steven Rostedt <srostedt@redhat.com>, Red Hat Inc.
 */

/*
 * Strategy: alter the .o file in-place.
 *
 * Append a new STRTAB that has the new section names, followed by a new array
 * ElfXX_Shdr[] that has the new section headers, followed by the section
 * contents for __mcount_loc and its relocations.  The old shstrtab strings,
 * and the old ElfXX_Shdr[] array, remain as "garbage" (commonly, a couple
 * kilobytes.)  Subsequent processing by /bin/ld (or the kernel module loader)
 * will ignore the garbage regions, because they are not designated by the
 * new .e_shoff nor the new ElfXX_Shdr[].  [In order to remove the garbage,
 * then use "ld -r" to create a new file that omits the garbage.]
 */

#include <sys/types.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <getopt.h>
#include <elf.h>
#include <fcntl.h>
#include <setjmp.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#ifndef EM_METAG
/* Remove this when these make it to the standard system elf.h. */
#define EM_METAG      174
#define R_METAG_ADDR32                   2
#define R_METAG_NONE                     3
#endif

static int fd_map;	/* File descriptor for file being modified. */
static int mmap_failed; /* Boolean flag. */
static void *ehdr_curr; /* current ElfXX_Ehdr *  for resource cleanup */
static char gpfx;	/* prefix for global symbol name (sometimes '_') */
static struct stat sb;	/* Remember .st_size, etc. */
static jmp_buf jmpenv;	/* setjmp/longjmp per-file error escape */
static const char *altmcount;	/* alternate mcount symbol name */
static int warn_on_notrace_sect; /* warn when section has mcount not being recorded */

/* setjmp() return values */
enum {
	SJ_SETJMP = 0,  /* hardwired first return */
	SJ_FAIL,
	SJ_SUCCEED
};

/* Per-file resource cleanup when multiple files. */
static void
cleanup(void)
{
	if (!mmap_failed)
		munmap(ehdr_curr, sb.st_size);
	else
		free(ehdr_curr);
	close(fd_map);
}

static void __attribute__((noreturn))
fail_file(void)
{
	cleanup();
	longjmp(jmpenv, SJ_FAIL);
}

static void __attribute__((noreturn))
succeed_file(void)
{
	cleanup();
	longjmp(jmpenv, SJ_SUCCEED);
}

/* ulseek, uread, ...:  Check return value for errors. */

static off_t
ulseek(int const fd, off_t const offset, int const whence)
{
	off_t const w = lseek(fd, offset, whence);
	if (w == (off_t)-1) {
		perror("lseek");
		fail_file();
	}
	return w;
}

static size_t
uread(int const fd, void *const buf, size_t const count)
{
	size_t const n = read(fd, buf, count);
	if (n != count) {
		perror("read");
		fail_file();
	}
	return n;
}

static size_t
uwrite(int const fd, void const *const buf, size_t const count)
{
	size_t const n = write(fd, buf, count);
	if (n != count) {
		perror("write");
		fail_file();
	}
	return n;
}

static void *
umalloc(size_t size)
{
	void *const addr = malloc(size);
	if (addr == 0) {
		fprintf(stderr, "malloc failed: %zu bytes\n", size);
		fail_file();
	}
	return addr;
}

static unsigned char ideal_nop5_x86_64[5] = { 0x0f, 0x1f, 0x44, 0x00, 0x00 };
static unsigned char ideal_nop5_x86_32[5] = { 0x3e, 0x8d, 0x74, 0x26, 0x00 };
static unsigned char *ideal_nop;

static char rel_type_nop;

static int (*make_nop)(void *map, size_t const offset);

static int make_nop_x86(void *map, size_t const offset)
{
	uint32_t *ptr;
	unsigned char *op;

	/* Confirm we have 0xe8 0x0 0x0 0x0 0x0 */
	ptr = map + offset;
	if (*ptr != 0)
		return -1;

	op = map + offset - 1;
	if (*op != 0xe8)
		return -1;

	/* convert to nop */
	ulseek(fd_map, offset - 1, SEEK_SET);
	uwrite(fd_map, ideal_nop, 5);
	return 0;
}

/*
 * Get the whole file as a programming convenience in order to avoid
 * malloc+lseek+read+free of many pieces.  If successful, then mmap
 * avoids copying unused pieces; else just read the whole file.
 * Open for both read and write; new info will be appended to the file.
 * Use MAP_PRIVATE so that a few changes to the in-memory ElfXX_Ehdr
 * do not propagate to the file until an explicit overwrite at the last.
 * This preserves most aspects of consistency (all except .st_size)
 * for simultaneous readers of the file while we are appending to it.
 * However, multiple writers still are bad.  We choose not to use
 * locking because it is expensive and the use case of kernel build
 * makes multiple writers unlikely.
 */
static void *mmap_file(char const *fname)
{
	void *addr;

	fd_map = open(fname, O_RDWR);
	if (fd_map < 0 || fstat(fd_map, &sb) < 0) {
		perror(fname);
		fail_file();
	}
	if (!S_ISREG(sb.st_mode)) {
		fprintf(stderr, "not a regular file: %s\n", fname);
		fail_file();
	}
	addr = mmap(0, sb.st_size, PROT_READ|PROT_WRITE, MAP_PRIVATE,
		    fd_map, 0);
	mmap_failed = 0;
	if (addr == MAP_FAILED) {
		mmap_failed = 1;
		addr = umalloc(sb.st_size);
		uread(fd_map, addr, sb.st_size);
	}
	return addr;
}

/* w8rev, w8nat, ...: Handle endianness. */

static uint64_t w8rev(uint64_t const x)
{
	return   ((0xff & (x >> (0 * 8))) << (7 * 8))
	       | ((0xff & (x >> (1 * 8))) << (6 * 8))
	       | ((0xff & (x >> (2 * 8))) << (5 * 8))
	       | ((0xff & (x >> (3 * 8))) << (4 * 8))
	       | ((0xff & (x >> (4 * 8))) << (3 * 8))
	       | ((0xff & (x >> (5 * 8))) << (2 * 8))
	       | ((0xff & (x >> (6 * 8))) << (1 * 8))
	       | ((0xff & (x >> (7 * 8))) << (0 * 8));
}

static uint32_t w4rev(uint32_t const x)
{
	return   ((0xff & (x >> (0 * 8))) << (3 * 8))
	       | ((0xff & (x >> (1 * 8))) << (2 * 8))
	       | ((0xff & (x >> (2 * 8))) << (1 * 8))
	       | ((0xff & (x >> (3 * 8))) << (0 * 8));
}

static uint32_t w2rev(uint16_t const x)
{
	return   ((0xff & (x >> (0 * 8))) << (1 * 8))
	       | ((0xff & (x >> (1 * 8))) << (0 * 8));
}

static uint64_t w8nat(uint64_t const x)
{
	return x;
}

static uint32_t w4nat(uint32_t const x)
{
	return x;
}

static uint32_t w2nat(uint16_t const x)
{
	return x;
}

static uint64_t (*w8)(uint64_t);
static uint32_t (*w)(uint32_t);
static uint32_t (*w2)(uint16_t);

/* Names of the sections that could contain calls to mcount. */
static int
is_mcounted_section_name(char const *const txtname)
{
	return strcmp(".text",           txtname) == 0 ||
		strcmp(".ref.text",      txtname) == 0 ||
		strcmp(".sched.text",    txtname) == 0 ||
		strcmp(".spinlock.text", txtname) == 0 ||
		strcmp(".irqentry.text", txtname) == 0 ||
		strcmp(".kprobes.text", txtname) == 0 ||
		strcmp(".text.unlikely", txtname) == 0;
}

/* 32 bit and 64 bit are very similar */
#include "recordmcount.h"
#define RECORD_MCOUNT_64
#include "recordmcount.h"

/* 64-bit EM_MIPS has weird ELF64_Rela.r_info.
 * http://techpubs.sgi.com/library/manuals/4000/007-4658-001/pdf/007-4658-001.pdf
 * We interpret Table 29 Relocation Operation (Elf64_Rel, Elf64_Rela) [p.40]
 * to imply the order of the members; the spec does not say so.
 *	typedef unsigned char Elf64_Byte;
 * fails on MIPS64 because their <elf.h> already has it!
 */

typedef uint8_t myElf64_Byte;		/* Type for a 8-bit quantity.  */

union mips_r_info {
	Elf64_Xword r_info;
	struct {
		Elf64_Word r_sym;		/* Symbol index.  */
		myElf64_Byte r_ssym;		/* Special symbol.  */
		myElf64_Byte r_type3;		/* Third relocation.  */
		myElf64_Byte r_type2;		/* Second relocation.  */
		myElf64_Byte r_type;		/* First relocation.  */
	} r_mips;
};

static uint64_t MIPS64_r_sym(Elf64_Rel const *rp)
{
	return w(((union mips_r_info){ .r_info = rp->r_info }).r_mips.r_sym);
}

static void MIPS64_r_info(Elf64_Rel *const rp, unsigned sym, unsigned type)
{
	rp->r_info = ((union mips_r_info){
		.r_mips = { .r_sym = w(sym), .r_type = type }
	}).r_info;
}

static void
do_file(char const *const fname)
{
	Elf32_Ehdr *const ehdr = mmap_file(fname);
	unsigned int reltype = 0;

	ehdr_curr = ehdr;
	w = w4nat;
	w2 = w2nat;
	w8 = w8nat;
	switch (ehdr->e_ident[EI_DATA]) {
		static unsigned int const endian = 1;
	default:
		fprintf(stderr, "unrecognized ELF data encoding %d: %s\n",
			ehdr->e_ident[EI_DATA], fname);
		fail_file();
		break;
	case ELFDATA2LSB:
		if (*(unsigned char const *)&endian != 1) {
			/* main() is big endian, file.o is little endian. */
			w = w4rev;
			w2 = w2rev;
			w8 = w8rev;
		}
		break;
	case ELFDATA2MSB:
		if (*(unsigned char const *)&endian != 0) {
			/* main() is little endian, file.o is big endian. */
			w = w4rev;
			w2 = w2rev;
			w8 = w8rev;
		}
		break;
	}  /* end switch */
	if (memcmp(ELFMAG, ehdr->e_ident, SELFMAG) != 0
	||  w2(ehdr->e_type) != ET_REL
	||  ehdr->e_ident[EI_VERSION] != EV_CURRENT) {
		fprintf(stderr, "unrecognized ET_REL file %s\n", fname);
		fail_file();
	}

	gpfx = 0;
	switch (w2(ehdr->e_machine)) {
	default:
		fprintf(stderr, "unrecognized e_machine %d %s\n",
			w2(ehdr->e_machine), fname);
		fail_file();
		break;
	case EM_386:
		reltype = R_386_32;
		make_nop = make_nop_x86;
		ideal_nop = ideal_nop5_x86_32;
		mcount_adjust_32 = -1;
		break;
	case EM_ARM:	 reltype = R_ARM_ABS32;
			 altmcount = "__gnu_mcount_nc";
			 break;
	case EM_IA_64:	 reltype = R_IA64_IMM64;   gpfx = '_'; break;
	case EM_METAG:	 reltype = R_METAG_ADDR32;
			 altmcount = "_mcount_wrapper";
			 rel_type_nop = R_METAG_NONE;
			 /* We happen to have the same requirement as MIPS */
			 is_fake_mcount32 = MIPS32_is_fake_mcount;
			 break;
	case EM_MIPS:	 /* reltype: e_class    */ gpfx = '_'; break;
	case EM_PPC:	 reltype = R_PPC_ADDR32;   gpfx = '_'; break;
	case EM_PPC64:	 reltype = R_PPC64_ADDR64; gpfx = '_'; break;
	case EM_S390:    /* reltype: e_class    */ gpfx = '_'; break;
	case EM_SH:	 reltype = R_SH_DIR32;                 break;
	case EM_SPARCV9: reltype = R_SPARC_64;     gpfx = '_'; break;
	case EM_X86_64:
		make_nop = make_nop_x86;
		ideal_nop = ideal_nop5_x86_64;
		reltype = R_X86_64_64;
		mcount_adjust_64 = -1;
		break;
	}  /* end switch */

	switch (ehdr->e_ident[EI_CLASS]) {
	default:
		fprintf(stderr, "unrecognized ELF class %d %s\n",
			ehdr->e_ident[EI_CLASS], fname);
		fail_file();
		break;
	case ELFCLASS32:
		if (w2(ehdr->e_ehsize) != sizeof(Elf32_Ehdr)
		||  w2(ehdr->e_shentsize) != sizeof(Elf32_Shdr)) {
			fprintf(stderr,
				"unrecognized ET_REL file: %s\n", fname);
			fail_file();
		}
		if (w2(ehdr->e_machine) == EM_S390) {
			reltype = R_390_32;
			mcount_adjust_32 = -4;
		}
		if (w2(ehdr->e_machine) == EM_MIPS) {
			reltype = R_MIPS_32;
			is_fake_mcount32 = MIPS32_is_fake_mcount;
		}
		do32(ehdr, fname, reltype);
		break;
	case ELFCLASS64: {
		Elf64_Ehdr *const ghdr = (Elf64_Ehdr *)ehdr;
		if (w2(ghdr->e_ehsize) != sizeof(Elf64_Ehdr)
		||  w2(ghdr->e_shentsize) != sizeof(Elf64_Shdr)) {
			fprintf(stderr,
				"unrecognized ET_REL file: %s\n", fname);
			fail_file();
		}
		if (w2(ghdr->e_machine) == EM_S390) {
			reltype = R_390_64;
			mcount_adjust_64 = -8;
		}
		if (w2(ghdr->e_machine) == EM_MIPS) {
			reltype = R_MIPS_64;
			Elf64_r_sym = MIPS64_r_sym;
			Elf64_r_info = MIPS64_r_info;
			is_fake_mcount64 = MIPS64_is_fake_mcount;
		}
		do64(ghdr, fname, reltype);
		break;
	}
	}  /* end switch */

	cleanup();
}

int
main(int argc, char *argv[])
{
	const char ftrace[] = "/ftrace.o";
	int ftrace_size = sizeof(ftrace) - 1;
	int n_error = 0;  /* gcc-4.3.0 false positive complaint */
	int c;
	int i;

	while ((c = getopt(argc, argv, "w")) >= 0) {
		switch (c) {
		case 'w':
			warn_on_notrace_sect = 1;
			break;
		default:
			fprintf(stderr, "usage: recordmcount [-w] file.o...\n");
			return 0;
		}
	}

	if ((argc - optind) < 1) {
		fprintf(stderr, "usage: recordmcount [-w] file.o...\n");
		return 0;
	}

	/* Process each file in turn, allowing deep failure. */
	for (i = optind; i < argc; i++) {
		char *file = argv[i];
		int const sjval = setjmp(jmpenv);
		int len;

		/*
		 * The file kernel/trace/ftrace.o references the mcount
		 * function but does not call it. Since ftrace.o should
		 * not be traced anyway, we just skip it.
		 */
		len = strlen(file);
		if (len >= ftrace_size &&
		    strcmp(file + (len - ftrace_size), ftrace) == 0)
			continue;

		switch (sjval) {
		default:
			fprintf(stderr, "internal error: %s\n", file);
			exit(1);
			break;
		case SJ_SETJMP:    /* normal sequence */
			/* Avoid problems if early cleanup() */
			fd_map = -1;
			ehdr_curr = NULL;
			mmap_failed = 1;
			do_file(file);
			break;
		case SJ_FAIL:    /* error in do_file or below */
			++n_error;
			break;
		case SJ_SUCCEED:    /* premature success */
			/* do nothing */
			break;
		}  /* end switch */
	}
	return !!n_error;
}