Edit File: recordmcount.c
/* * 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(".cpuidle.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; }