genelf_debug.c

Go to the documentation of this file.

/*
 * genelf_debug.c
 * Copyright (C) 2015, Google, Inc
 *
 * Contributed by:
 *  Stephane Eranian <eranian@google.com>
 *
 * Released under the GPL v2.
 *
 * based on GPLv2 source code from Oprofile
 * @remark Copyright 2007 OProfile authors
 * @author Philippe Elie
 */
#include <linux/compiler.h>
#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>
#include <dwarf.h>

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

#define BUFFER_EXT_DFL_SIZE (4 * 1024)

typedef uint32_t uword;
typedef uint16_t uhalf;
typedef int32_t  sword;
typedef int16_t  shalf;
typedef uint8_t  ubyte;
typedef int8_t   sbyte;

struct buffer_ext {
    size_t cur_pos;
    size_t max_sz;
    void *data;
};

static void
buffer_ext_dump(struct buffer_ext *be, const char *msg)
{
    size_t i;
    warnx("DUMP for %s", msg);
    for (i = 0 ; i < be->cur_pos; i++)
        warnx("%4zu 0x%02x", i, (((char *)be->data)[i]) & 0xff);
}

static inline int
buffer_ext_add(struct buffer_ext *be, void *addr, size_t sz)
{
    void *tmp;
    size_t be_sz = be->max_sz;

retry:
    if ((be->cur_pos + sz) < be_sz) {
        memcpy(be->data + be->cur_pos, addr, sz);
        be->cur_pos += sz;
        return 0;
    }

    if (!be_sz)
        be_sz = BUFFER_EXT_DFL_SIZE;
    else
        be_sz <<= 1;

    tmp = realloc(be->data, be_sz);
    if (!tmp)
        return -1;

    be->data   = tmp;
    be->max_sz = be_sz;

    goto retry;
}

static void
buffer_ext_init(struct buffer_ext *be)
{
    be->data = NULL;
    be->cur_pos = 0;
    be->max_sz = 0;
}

static inline size_t
buffer_ext_size(struct buffer_ext *be)
{
    return be->cur_pos;
}

static inline void *
buffer_ext_addr(struct buffer_ext *be)
{
    return be->data;
}

struct debug_line_header {
    // Not counting this field
    uword total_length;
    // version number (2 currently)
    uhalf version;
    // relative offset from next field to
    // program statement
    uword prolog_length;
    ubyte minimum_instruction_length;
    ubyte default_is_stmt;
    // line_base - see DWARF 2 specs
    sbyte line_base;
    // line_range - see DWARF 2 specs
    ubyte line_range;
    // number of opcode + 1
    ubyte opcode_base;
    /* follow the array of opcode args nr: ubytes [nr_opcode_base] */
    /* follow the search directories index, zero terminated string
     * terminated by an empty string.
     */
    /* follow an array of { filename, LEB128, LEB128, LEB128 }, first is
     * the directory index entry, 0 means current directory, then mtime
     * and filesize, last entry is followed by en empty string.
     */
    /* follow the first program statement */
} __packed;

/* DWARF 2 spec talk only about one possible compilation unit header while
 * binutils can handle two flavours of dwarf 2, 32 and 64 bits, this is not
 * related to the used arch, an ELF 32 can hold more than 4 Go of debug
 * information. For now we handle only DWARF 2 32 bits comp unit. It'll only
 * become a problem if we generate more than 4GB of debug information.
 */
struct compilation_unit_header {
    uword total_length;
    uhalf version;
    uword debug_abbrev_offset;
    ubyte pointer_size;
} __packed;

#define DW_LNS_num_opcode (DW_LNS_set_isa + 1)

/* field filled at run time are marked with -1 */
static struct debug_line_header const default_debug_line_header = {
    .total_length = -1,
    .version = 2,
    .prolog_length = -1,
    .minimum_instruction_length = 1,    /* could be better when min instruction size != 1 */
    .default_is_stmt = 1,   /* we don't take care about basic block */
    .line_base = -5,    /* sensible value for line base ... */
    .line_range = -14,     /* ... and line range are guessed statically */
    .opcode_base = DW_LNS_num_opcode
};

static ubyte standard_opcode_length[] =
{
    0, 1, 1, 1, 1, 0, 0, 0, 1, 0, 0, 1
};
#if 0
{
    [DW_LNS_advance_pc]   = 1,
    [DW_LNS_advance_line] = 1,
    [DW_LNS_set_file] =  1,
    [DW_LNS_set_column] = 1,
    [DW_LNS_fixed_advance_pc] = 1,
    [DW_LNS_set_isa] = 1,
};
#endif

/* field filled at run time are marked with -1 */
static struct compilation_unit_header default_comp_unit_header = {
    .total_length = -1,
    .version = 2,
    .debug_abbrev_offset = 0,     /* we reuse the same abbrev entries for all comp unit */
    .pointer_size = sizeof(void *)
};

static void emit_uword(struct buffer_ext *be, uword data)
{
    buffer_ext_add(be, &data, sizeof(uword));
}

static void emit_string(struct buffer_ext *be, const char *s)
{
    buffer_ext_add(be, (void *)s, strlen(s) + 1);
}

static void emit_unsigned_LEB128(struct buffer_ext *be,
                 unsigned long data)
{
    do {
        ubyte cur = data & 0x7F;
        data >>= 7;
        if (data)
            cur |= 0x80;
        buffer_ext_add(be, &cur, 1);
    } while (data);
}

static void emit_signed_LEB128(struct buffer_ext *be, long data)
{
    int more = 1;
    int negative = data < 0;
    int size = sizeof(long) * CHAR_BIT;
    while (more) {
        ubyte cur = data & 0x7F;
        data >>= 7;
        if (negative)
            data |= - (1 << (size - 7));
        if ((data == 0 && !(cur & 0x40)) ||
            (data == -1l && (cur & 0x40)))
            more = 0;
        else
            cur |= 0x80;
        buffer_ext_add(be, &cur, 1);
    }
}

static void emit_extended_opcode(struct buffer_ext *be, ubyte opcode,
                 void *data, size_t data_len)
{
    buffer_ext_add(be, (char *)"", 1);

    emit_unsigned_LEB128(be, data_len + 1);

    buffer_ext_add(be, &opcode, 1);
    buffer_ext_add(be, data, data_len);
}

static void emit_opcode(struct buffer_ext *be, ubyte opcode)
{
    buffer_ext_add(be, &opcode, 1);
}

static void emit_opcode_signed(struct buffer_ext  *be,
                   ubyte opcode, long data)
{
    buffer_ext_add(be, &opcode, 1);
    emit_signed_LEB128(be, data);
}

static void emit_opcode_unsigned(struct buffer_ext *be, ubyte opcode,
                 unsigned long data)
{
    buffer_ext_add(be, &opcode, 1);
    emit_unsigned_LEB128(be, data);
}

static void emit_advance_pc(struct buffer_ext *be, unsigned long delta_pc)
{
    emit_opcode_unsigned(be, DW_LNS_advance_pc, delta_pc);
}

static void emit_advance_lineno(struct buffer_ext  *be, long delta_lineno)
{
    emit_opcode_signed(be, DW_LNS_advance_line, delta_lineno);
}

static void emit_lne_end_of_sequence(struct buffer_ext *be)
{
    emit_extended_opcode(be, DW_LNE_end_sequence, NULL, 0);
}

static void emit_set_file(struct buffer_ext *be, unsigned long idx)
{
    emit_opcode_unsigned(be, DW_LNS_set_file, idx);
}

static void emit_lne_define_filename(struct buffer_ext *be,
                     const char *filename)
{
    buffer_ext_add(be, (void *)"", 1);

    /* LNE field, strlen(filename) + zero termination, 3 bytes for: the dir entry, timestamp, filesize */
    emit_unsigned_LEB128(be, strlen(filename) + 5);
    emit_opcode(be, DW_LNE_define_file);
    emit_string(be, filename);
    /* directory index 0=do not know */
        emit_unsigned_LEB128(be, 0);
    /* last modification date on file 0=do not know */
        emit_unsigned_LEB128(be, 0);
    /* filesize 0=do not know */
        emit_unsigned_LEB128(be, 0);
}

static void emit_lne_set_address(struct buffer_ext *be,
                 void *address)
{
    emit_extended_opcode(be, DW_LNE_set_address, &address, sizeof(unsigned long));
}

static ubyte get_special_opcode(struct debug_entry *ent,
                unsigned int last_line,
                unsigned long last_vma)
{
    unsigned int temp;
    unsigned long delta_addr;

    /*
     * delta from line_base
     */
    temp = (ent->lineno - last_line) - default_debug_line_header.line_base;

    if (temp >= default_debug_line_header.line_range)
        return 0;

    /*
     * delta of addresses
     */
    delta_addr = (ent->addr - last_vma) / default_debug_line_header.minimum_instruction_length;

    /* This is not sufficient to ensure opcode will be in [0-256] but
     * sufficient to ensure when summing with the delta lineno we will
     * not overflow the unsigned long opcode */

    if (delta_addr <= 256 / default_debug_line_header.line_range) {
        unsigned long opcode = temp +
            (delta_addr * default_debug_line_header.line_range) +
            default_debug_line_header.opcode_base;

        return opcode <= 255 ? opcode : 0;
    }
    return 0;
}

static void emit_lineno_info(struct buffer_ext *be,
                 struct debug_entry *ent, size_t nr_entry,
                 unsigned long code_addr)
{
    size_t i;

    /*
     * Machine state at start of a statement program
     * address = 0
     * file    = 1
     * line    = 1
     * column  = 0
     * is_stmt = default_is_stmt as given in the debug_line_header
     * basic block = 0
     * end sequence = 0
     */

    /* start state of the state machine we take care of */
    unsigned long last_vma = code_addr;
    char const  *cur_filename = NULL;
    unsigned long cur_file_idx = 0;
    int last_line = 1;

    emit_lne_set_address(be, (void *)code_addr);

    for (i = 0; i < nr_entry; i++, ent = debug_entry_next(ent)) {
        int need_copy = 0;
        ubyte special_opcode;

        /*
         * check if filename changed, if so add it
         */
        if (!cur_filename || strcmp(cur_filename, ent->name)) {
            emit_lne_define_filename(be, ent->name);
            cur_filename = ent->name;
            emit_set_file(be, ++cur_file_idx);
            need_copy = 1;
        }

        special_opcode = get_special_opcode(ent, last_line, last_vma);
        if (special_opcode != 0) {
            last_line = ent->lineno;
            last_vma  = ent->addr;
            emit_opcode(be, special_opcode);
        } else {
            /*
             * lines differ, emit line delta
             */
            if (last_line != ent->lineno) {
                emit_advance_lineno(be, ent->lineno - last_line);
                last_line = ent->lineno;
                need_copy = 1;
            }
            /*
             * addresses differ, emit address delta
             */
            if (last_vma != ent->addr) {
                emit_advance_pc(be, ent->addr - last_vma);
                last_vma = ent->addr;
                need_copy = 1;
            }
            /*
             * add new row to matrix
             */
            if (need_copy)
                emit_opcode(be, DW_LNS_copy);
        }
    }
}

static void add_debug_line(struct buffer_ext *be,
    struct debug_entry *ent, size_t nr_entry,
    unsigned long code_addr)
{
    struct debug_line_header * dbg_header;
    size_t old_size;

    old_size = buffer_ext_size(be);

    buffer_ext_add(be, (void *)&default_debug_line_header,
         sizeof(default_debug_line_header));

    buffer_ext_add(be, &standard_opcode_length,  sizeof(standard_opcode_length));

    // empty directory entry
    buffer_ext_add(be, (void *)"", 1);

    // empty filename directory
    buffer_ext_add(be, (void *)"", 1);

    dbg_header = buffer_ext_addr(be) + old_size;
    dbg_header->prolog_length = (buffer_ext_size(be) - old_size) -
        offsetof(struct debug_line_header, minimum_instruction_length);

    emit_lineno_info(be, ent, nr_entry, code_addr);

    emit_lne_end_of_sequence(be);

    dbg_header = buffer_ext_addr(be) + old_size;
    dbg_header->total_length = (buffer_ext_size(be) - old_size) -
        offsetof(struct debug_line_header, version);
}

static void
add_debug_abbrev(struct buffer_ext *be)
{
        emit_unsigned_LEB128(be, 1);
        emit_unsigned_LEB128(be, DW_TAG_compile_unit);
        emit_unsigned_LEB128(be, DW_CHILDREN_yes);
        emit_unsigned_LEB128(be, DW_AT_stmt_list);
        emit_unsigned_LEB128(be, DW_FORM_data4);
        emit_unsigned_LEB128(be, 0);
        emit_unsigned_LEB128(be, 0);
        emit_unsigned_LEB128(be, 0);
}

static void
add_compilation_unit(struct buffer_ext *be,
             size_t offset_debug_line)
{
    struct compilation_unit_header *comp_unit_header;
    size_t old_size = buffer_ext_size(be);

    buffer_ext_add(be, &default_comp_unit_header,
               sizeof(default_comp_unit_header));

    emit_unsigned_LEB128(be, 1);
    emit_uword(be, offset_debug_line);

    comp_unit_header = buffer_ext_addr(be) + old_size;
    comp_unit_header->total_length = (buffer_ext_size(be) - old_size) -
        offsetof(struct compilation_unit_header, version);
}

static int
jit_process_debug_info(uint64_t code_addr,
               void *debug, int nr_debug_entries,
               struct buffer_ext *dl,
               struct buffer_ext *da,
               struct buffer_ext *di)
{
    struct debug_entry *ent = debug;
    int i;

    for (i = 0; i < nr_debug_entries; i++) {
        ent->addr = ent->addr - code_addr;
        ent = debug_entry_next(ent);
    }
    add_compilation_unit(di, buffer_ext_size(dl));
    add_debug_line(dl, debug, nr_debug_entries, 0);
    add_debug_abbrev(da);
    if (0) buffer_ext_dump(da, "abbrev");

    return 0;
}

int
jit_add_debug_info(Elf *e, uint64_t code_addr, void *debug, int nr_debug_entries)
{
    Elf_Data *d;
    Elf_Scn *scn;
    Elf_Shdr *shdr;
    struct buffer_ext dl, di, da;
    int ret;

    buffer_ext_init(&dl);
    buffer_ext_init(&di);
    buffer_ext_init(&da);

    ret = jit_process_debug_info(code_addr, debug, nr_debug_entries, &dl, &da, &di);
    if (ret)
        return -1;
    /*
     * setup .debug_line 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 = 1;
    d->d_off = 0LL;
    d->d_buf = buffer_ext_addr(&dl);
    d->d_type = ELF_T_BYTE;
    d->d_size = buffer_ext_size(&dl);
    d->d_version = EV_CURRENT;

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

    shdr->sh_name = 52; /* .debug_line */
    shdr->sh_type = SHT_PROGBITS;
    shdr->sh_addr = 0; /* must be zero or == sh_offset -> dynamic object */
    shdr->sh_flags = 0;
    shdr->sh_entsize = 0;

    /*
     * setup .debug_info 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 = 1;
    d->d_off = 0LL;
    d->d_buf = buffer_ext_addr(&di);
    d->d_type = ELF_T_BYTE;
    d->d_size = buffer_ext_size(&di);
    d->d_version = EV_CURRENT;

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

    shdr->sh_name = 64; /* .debug_info */
    shdr->sh_type = SHT_PROGBITS;
    shdr->sh_addr = 0; /* must be zero or == sh_offset -> dynamic object */
    shdr->sh_flags = 0;
    shdr->sh_entsize = 0;

    /*
     * setup .debug_abbrev 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 = 1;
    d->d_off = 0LL;
    d->d_buf = buffer_ext_addr(&da);
    d->d_type = ELF_T_BYTE;
    d->d_size = buffer_ext_size(&da);
    d->d_version = EV_CURRENT;

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

    shdr->sh_name = 76; /* .debug_info */
    shdr->sh_type = SHT_PROGBITS;
    shdr->sh_addr = 0; /* must be zero or == sh_offset -> dynamic object */
    shdr->sh_flags = 0;
    shdr->sh_entsize = 0;

    /*
     * now we update the ELF image with all the sections
     */
    if (elf_update(e, ELF_C_WRITE) < 0) {
        warnx("elf_update debug failed");
        return -1;
    }
    return 0;
}