genelf.c

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/*
 * genelf.c
 * Copyright (C) 2014, Google, Inc
 *
 * Contributed by:
 *  Stephane Eranian <eranian@gmail.com>
 *
 * Released under the GPL v2. (and only v2, not any later version)
 */

#include <sys/types.h>
#include <stdio.h>
#include <getopt.h>
#include <stddef.h>
#include <libelf.h>
#include <string.h>
#include <stdlib.h>
#include <inttypes.h>
#include <limits.h>
#include <fcntl.h>
#include <err.h>
#ifdef HAVE_DWARF_SUPPORT
#include <dwarf.h>
#endif

#include "perf.h"
#include "genelf.h"
#include "../util/jitdump.h"

#ifndef NT_GNU_BUILD_ID
#define NT_GNU_BUILD_ID 3
#endif

#define JVMTI

#define BUILD_ID_URANDOM /* different uuid for each run */

#ifdef HAVE_LIBCRYPTO

#define BUILD_ID_MD5
#undef BUILD_ID_SHA /* does not seem to work well when linked with Java */
#undef BUILD_ID_URANDOM /* different uuid for each run */

#ifdef BUILD_ID_SHA
#include <openssl/sha.h>
#endif

#ifdef BUILD_ID_MD5
#include <openssl/md5.h>
#endif
#endif


typedef struct {
  unsigned int namesz;  /* Size of entry's owner string */
  unsigned int descsz;  /* Size of the note descriptor */
  unsigned int type;    /* Interpretation of the descriptor */
  char         name[0]; /* Start of the name+desc data */
} Elf_Note;

struct options {
    char *output;
    int fd;
};

static char shd_string_table[] = {
    0,
    '.', 't', 'e', 'x', 't', 0,         /*  1 */
    '.', 's', 'h', 's', 't', 'r', 't', 'a', 'b', 0, /*  7 */
    '.', 's', 'y', 'm', 't', 'a', 'b', 0,       /* 17 */
    '.', 's', 't', 'r', 't', 'a', 'b', 0,       /* 25 */
    '.', 'n', 'o', 't', 'e', '.', 'g', 'n', 'u', '.', 'b', 'u', 'i', 'l', 'd', '-', 'i', 'd', 0, /* 33 */
    '.', 'd', 'e', 'b', 'u', 'g', '_', 'l', 'i', 'n', 'e', 0, /* 52 */
    '.', 'd', 'e', 'b', 'u', 'g', '_', 'i', 'n', 'f', 'o', 0, /* 64 */
    '.', 'd', 'e', 'b', 'u', 'g', '_', 'a', 'b', 'b', 'r', 'e', 'v', 0, /* 76 */
    '.', 'e', 'h', '_', 'f', 'r', 'a', 'm', 'e', '_', 'h', 'd', 'r', 0, /* 90 */
    '.', 'e', 'h', '_', 'f', 'r', 'a', 'm', 'e', 0, /* 104 */
};

static struct buildid_note {
    Elf_Note desc;      /* descsz: size of build-id, must be multiple of 4 */
    char     name[4];   /* GNU\0 */
    char     build_id[20];
} bnote;

static Elf_Sym symtab[]={
    /* symbol 0 MUST be the undefined symbol */
    { .st_name  = 0, /* index in sym_string table */
      .st_info  = ELF_ST_TYPE(STT_NOTYPE),
      .st_shndx = 0, /* for now */
      .st_value = 0x0,
      .st_other = ELF_ST_VIS(STV_DEFAULT),
      .st_size  = 0,
    },
    { .st_name  = 1, /* index in sym_string table */
      .st_info  = ELF_ST_BIND(STB_LOCAL) | ELF_ST_TYPE(STT_FUNC),
      .st_shndx = 1,
      .st_value = 0, /* for now */
      .st_other = ELF_ST_VIS(STV_DEFAULT),
      .st_size  = 0, /* for now */
    }
};

#ifdef BUILD_ID_URANDOM
static void
gen_build_id(struct buildid_note *note,
         unsigned long load_addr __maybe_unused,
         const void *code __maybe_unused,
         size_t csize __maybe_unused)
{
    int fd;
    size_t sz = sizeof(note->build_id);
    ssize_t sret;

    fd = open("/dev/urandom", O_RDONLY);
    if (fd == -1)
        err(1, "cannot access /dev/urandom for buildid");

    sret = read(fd, note->build_id, sz);

    close(fd);

    if (sret != (ssize_t)sz)
        memset(note->build_id, 0, sz);
}
#endif

#ifdef BUILD_ID_SHA
static void
gen_build_id(struct buildid_note *note,
         unsigned long load_addr __maybe_unused,
         const void *code,
         size_t csize)
{
    if (sizeof(note->build_id) < SHA_DIGEST_LENGTH)
        errx(1, "build_id too small for SHA1");

    SHA1(code, csize, (unsigned char *)note->build_id);
}
#endif

#ifdef BUILD_ID_MD5
static void
gen_build_id(struct buildid_note *note, unsigned long load_addr, const void *code, size_t csize)
{
    MD5_CTX context;

    if (sizeof(note->build_id) < 16)
        errx(1, "build_id too small for MD5");

    MD5_Init(&context);
    MD5_Update(&context, &load_addr, sizeof(load_addr));
    MD5_Update(&context, code, csize);
    MD5_Final((unsigned char *)note->build_id, &context);
}
#endif

static int
jit_add_eh_frame_info(Elf *e, void* unwinding, uint64_t unwinding_header_size,
              uint64_t unwinding_size, uint64_t base_offset)
{
    Elf_Data *d;
    Elf_Scn *scn;
    Elf_Shdr *shdr;
    uint64_t unwinding_table_size = unwinding_size - unwinding_header_size;

    /*
     * setup eh_frame section
     */
    scn = elf_newscn(e);
    if (!scn) {
        warnx("cannot create section");
        return -1;
    }

    d = elf_newdata(scn);
    if (!d) {
        warnx("cannot get new data");
        return -1;
    }

    d->d_align = 8;
    d->d_off = 0LL;
    d->d_buf = unwinding;
    d->d_type = ELF_T_BYTE;
    d->d_size = unwinding_table_size;
    d->d_version = EV_CURRENT;

    shdr = elf_getshdr(scn);
    if (!shdr) {
        warnx("cannot get section header");
        return -1;
    }

    shdr->sh_name = 104;
    shdr->sh_type = SHT_PROGBITS;
    shdr->sh_addr = base_offset;
    shdr->sh_flags = SHF_ALLOC;
    shdr->sh_entsize = 0;

    /*
     * setup eh_frame_hdr section
     */
    scn = elf_newscn(e);
    if (!scn) {
        warnx("cannot create section");
        return -1;
    }

    d = elf_newdata(scn);
    if (!d) {
        warnx("cannot get new data");
        return -1;
    }

    d->d_align = 4;
    d->d_off = 0LL;
    d->d_buf = unwinding + unwinding_table_size;
    d->d_type = ELF_T_BYTE;
    d->d_size = unwinding_header_size;
    d->d_version = EV_CURRENT;

    shdr = elf_getshdr(scn);
    if (!shdr) {
        warnx("cannot get section header");
        return -1;
    }

    shdr->sh_name = 90;
    shdr->sh_type = SHT_PROGBITS;
    shdr->sh_addr = base_offset + unwinding_table_size;
    shdr->sh_flags = SHF_ALLOC;
    shdr->sh_entsize = 0;

    return 0;
}

/*
 * fd: file descriptor open for writing for the output file
 * load_addr: code load address (could be zero, just used for buildid)
 * sym: function name (for native code - used as the symbol)
 * code: the native code
 * csize: the code size in bytes
 */
int
jit_write_elf(int fd, uint64_t load_addr, const char *sym,
          const void *code, int csize,
          void *debug __maybe_unused, int nr_debug_entries __maybe_unused,
          void *unwinding, uint64_t unwinding_header_size, uint64_t unwinding_size)
{
    Elf *e;
    Elf_Data *d;
    Elf_Scn *scn;
    Elf_Ehdr *ehdr;
    Elf_Shdr *shdr;
    uint64_t eh_frame_base_offset;
    char *strsym = NULL;
    int symlen;
    int retval = -1;

    if (elf_version(EV_CURRENT) == EV_NONE) {
        warnx("ELF initialization failed");
        return -1;
    }

    e = elf_begin(fd, ELF_C_WRITE, NULL);
    if (!e) {
        warnx("elf_begin failed");
        goto error;
    }

    /*
     * setup ELF header
     */
    ehdr = elf_newehdr(e);
    if (!ehdr) {
        warnx("cannot get ehdr");
        goto error;
    }

    ehdr->e_ident[EI_DATA] = GEN_ELF_ENDIAN;
    ehdr->e_ident[EI_CLASS] = GEN_ELF_CLASS;
    ehdr->e_machine = GEN_ELF_ARCH;
    ehdr->e_type = ET_DYN;
    ehdr->e_entry = GEN_ELF_TEXT_OFFSET;
    ehdr->e_version = EV_CURRENT;
    ehdr->e_shstrndx= unwinding ? 4 : 2; /* shdr index for section name */

    /*
     * setup text section
     */
    scn = elf_newscn(e);
    if (!scn) {
        warnx("cannot create section");
        goto error;
    }

    d = elf_newdata(scn);
    if (!d) {
        warnx("cannot get new data");
        goto error;
    }

    d->d_align = 16;
    d->d_off = 0LL;
    d->d_buf = (void *)code;
    d->d_type = ELF_T_BYTE;
    d->d_size = csize;
    d->d_version = EV_CURRENT;

    shdr = elf_getshdr(scn);
    if (!shdr) {
        warnx("cannot get section header");
        goto error;
    }

    shdr->sh_name = 1;
    shdr->sh_type = SHT_PROGBITS;
    shdr->sh_addr = GEN_ELF_TEXT_OFFSET;
    shdr->sh_flags = SHF_EXECINSTR | SHF_ALLOC;
    shdr->sh_entsize = 0;

    /*
     * Setup .eh_frame_hdr and .eh_frame
     */
    if (unwinding) {
        eh_frame_base_offset = ALIGN_8(GEN_ELF_TEXT_OFFSET + csize);
        retval = jit_add_eh_frame_info(e, unwinding,
                           unwinding_header_size, unwinding_size,
                           eh_frame_base_offset);
        if (retval)
            goto error;
    }

    /*
     * setup section headers string table
     */
    scn = elf_newscn(e);
    if (!scn) {
        warnx("cannot create section");
        goto error;
    }

    d = elf_newdata(scn);
    if (!d) {
        warnx("cannot get new data");
        goto error;
    }

    d->d_align = 1;
    d->d_off = 0LL;
    d->d_buf = shd_string_table;
    d->d_type = ELF_T_BYTE;
    d->d_size = sizeof(shd_string_table);
    d->d_version = EV_CURRENT;

    shdr = elf_getshdr(scn);
    if (!shdr) {
        warnx("cannot get section header");
        goto error;
    }

    shdr->sh_name = 7; /* offset of '.shstrtab' in shd_string_table */
    shdr->sh_type = SHT_STRTAB;
    shdr->sh_flags = 0;
    shdr->sh_entsize = 0;

    /*
     * setup symtab section
     */
    symtab[1].st_size  = csize;
    symtab[1].st_value = GEN_ELF_TEXT_OFFSET;

    scn = elf_newscn(e);
    if (!scn) {
        warnx("cannot create section");
        goto error;
    }

    d = elf_newdata(scn);
    if (!d) {
        warnx("cannot get new data");
        goto error;
    }

    d->d_align = 8;
    d->d_off = 0LL;
    d->d_buf = symtab;
    d->d_type = ELF_T_SYM;
    d->d_size = sizeof(symtab);
    d->d_version = EV_CURRENT;

    shdr = elf_getshdr(scn);
    if (!shdr) {
        warnx("cannot get section header");
        goto error;
    }

    shdr->sh_name = 17; /* offset of '.symtab' in shd_string_table */
    shdr->sh_type = SHT_SYMTAB;
    shdr->sh_flags = 0;
    shdr->sh_entsize = sizeof(Elf_Sym);
    shdr->sh_link = unwinding ? 6 : 4; /* index of .strtab section */

    /*
     * setup symbols string table
     * 2 = 1 for 0 in 1st entry, 1 for the 0 at end of symbol for 2nd entry
     */
    symlen = 2 + strlen(sym);
    strsym = calloc(1, symlen);
    if (!strsym) {
        warnx("cannot allocate strsym");
        goto error;
    }
    strcpy(strsym + 1, sym);

    scn = elf_newscn(e);
    if (!scn) {
        warnx("cannot create section");
        goto error;
    }

    d = elf_newdata(scn);
    if (!d) {
        warnx("cannot get new data");
        goto error;
    }

    d->d_align = 1;
    d->d_off = 0LL;
    d->d_buf = strsym;
    d->d_type = ELF_T_BYTE;
    d->d_size = symlen;
    d->d_version = EV_CURRENT;

    shdr = elf_getshdr(scn);
    if (!shdr) {
        warnx("cannot get section header");
        goto error;
    }

    shdr->sh_name = 25; /* offset in shd_string_table */
    shdr->sh_type = SHT_STRTAB;
    shdr->sh_flags = 0;
    shdr->sh_entsize = 0;

    /*
     * setup build-id section
     */
    scn = elf_newscn(e);
    if (!scn) {
        warnx("cannot create section");
        goto error;
    }

    d = elf_newdata(scn);
    if (!d) {
        warnx("cannot get new data");
        goto error;
    }

    /*
     * build-id generation
     */
    gen_build_id(&bnote, load_addr, code, csize);
    bnote.desc.namesz = sizeof(bnote.name); /* must include 0 termination */
    bnote.desc.descsz = sizeof(bnote.build_id);
    bnote.desc.type   = NT_GNU_BUILD_ID;
    strcpy(bnote.name, "GNU");

    d->d_align = 4;
    d->d_off = 0LL;
    d->d_buf = &bnote;
    d->d_type = ELF_T_BYTE;
    d->d_size = sizeof(bnote);
    d->d_version = EV_CURRENT;

    shdr = elf_getshdr(scn);
    if (!shdr) {
        warnx("cannot get section header");
        goto error;
    }

    shdr->sh_name = 33; /* offset in shd_string_table */
    shdr->sh_type = SHT_NOTE;
    shdr->sh_addr = 0x0;
    shdr->sh_flags = SHF_ALLOC;
    shdr->sh_size = sizeof(bnote);
    shdr->sh_entsize = 0;

#ifdef HAVE_DWARF_SUPPORT
    if (debug && nr_debug_entries) {
        retval = jit_add_debug_info(e, load_addr, debug, nr_debug_entries);
        if (retval)
            goto error;
    } else
#endif
    {
        if (elf_update(e, ELF_C_WRITE) < 0) {
            warnx("elf_update 4 failed");
            goto error;
        }
    }

    retval = 0;
error:
    (void)elf_end(e);

    free(strsym);


    return retval;
}

#ifndef JVMTI

static unsigned char x86_code[] = {
    0xBB, 0x2A, 0x00, 0x00, 0x00, /* movl $42, %ebx */
    0xB8, 0x01, 0x00, 0x00, 0x00, /* movl $1, %eax */
    0xCD, 0x80            /* int $0x80 */
};

static struct options options;

int main(int argc, char **argv)
{
    int c, fd, ret;

    while ((c = getopt(argc, argv, "o:h")) != -1) {
        switch (c) {
        case 'o':
            options.output = optarg;
            break;
        case 'h':
            printf("Usage: genelf -o output_file [-h]\n");
            return 0;
        default:
            errx(1, "unknown option");
        }
    }

    fd = open(options.output, O_CREAT|O_TRUNC|O_RDWR, 0666);
    if (fd == -1)
        err(1, "cannot create file %s", options.output);

    ret = jit_write_elf(fd, "main", x86_code, sizeof(x86_code));
    close(fd);

    if (ret != 0)
        unlink(options.output);

    return ret;
}
#endif