recordmcount.c

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/*
 * recordmcount.c: construct a table of the locations of calls to 'mcount'
 * so that ftrace can find them quickly.
 * Copyright 2009 John F. Reiser <[email protected]>.  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 <[email protected]>, 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>

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_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;
}