如何从libopcodes获取指令信息？

Z时代
2024-01-10
分类：问答

我正在编写一个在x86-32和x86-64

Linux中使用libbfd和libopcodes进行反汇编的工具。问题是，尽管我能够分解libopcode，但无法获得任何指令信息。为了演示起见，我举了一个最小的例子来重现我的问题。该程序应从入口点反汇编到第一个RET/

RETQ。

该代码有点被全局变量所破坏，为简洁起见，省略了错误检查等，但是应该清楚地说明问题。

#include <bfd.h>
#include <dis-asm.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <string.h>
#include <ctype.h>
#include <limits.h>
#include <libiberty.h>
/*
 * Holds state for BFD and libopcodes.
 */
bfd *        abfd  = NULL;
disassemble_info dinfo = {0};
/*
 * Temporary hack to signal when disassembling should stop.
 */
static bool stop_disassembling = FALSE;
/*
 * Gets path to currently running executable.
 */
bool get_target_path(char * target_path, size_t size)
{
    char *   path;
    ssize_t len;
    pid_t pid = getpid();
    sprintf(target_path, "/proc/%d/exe", (int)pid );
    path = strdup(target_path);
    len  = readlink(path, target_path, size);
    target_path[len] = '\0';
    free(path);
    return TRUE;
}
/*
 * libopcodes appends spaces on the end of some instructions so for
 * comparisons, we want to strip those first.
 */
void strip_tail(char * str, unsigned int size)
{
    int i;
    for(i = 0; i < size; i++) {
        if(!isgraph(str[i])) {
            str[i] = '\0';
            break;
        }
    }
}
/*
 * Checks whether the current instruction will cause the control flow to not
 * proceed to the linearly subsequent instruction (e.g. ret, jmp, etc.)
 */
bool breaks_control_flow(char * str)
{
    if(abfd->arch_info->bits_per_address == 64) {
        if(strcmp(str, "retq") == 0) {
            return TRUE;
        }
    } else {
        if(strcmp(str, "ret") == 0) {
            return TRUE;
        }
    }
    return FALSE;
}
/*
 * Used as a callback for libopcodes so we can do something useful with the
 * disassembly. Currently this just outputs to stdout.
 */
int custom_fprintf(void * stream, const char * format, ...)
{
    /* silly amount */
    char    str[128] = {0};
    int rv;
    va_list args;
    va_start(args, format);
    rv = vsnprintf(str, ARRAY_SIZE(str) - 1, format, args);
    va_end(args);
    puts(str);
    strip_tail(str, ARRAY_SIZE(str));
    if(breaks_control_flow(str)) {
        puts("Stopped disassembly");
        stop_disassembling = TRUE;
    }
    if(dinfo.insn_info_valid) {
        switch(dinfo.insn_type) {
            case dis_noninsn:
                printf("not an instruction\n");
                break;
            case dis_nonbranch:
                printf("not a branch\n");
                break;
            case dis_branch:
                printf("is a branch\n");
                break;
            case dis_condbranch:
                printf("is a conditional branch\n");
                break;
            case dis_jsr:
                printf("jump to subroutine\n");
                break;
            case dis_condjsr:
                printf("conditional jump to subroutine\n");
                break;
            case dis_dref:
                printf("data reference in instruction\n");
                break;
            case dis_dref2:
                printf("two data references in instruction\n");
                break;
            default:
                printf("not enumerated\n");
                break;
        }
    } else {
        printf("insn_info not valid\n");
    }
    return rv;
}
/*
 * Initialises libopcodes disassembler and returns an instance of it.
 */
disassembler_ftype init_disasm(bfd * abfd, disassemble_info * dinfo)
{
    /* Override the stream the disassembler outputs to */
    init_disassemble_info(dinfo, NULL, custom_fprintf);
    dinfo->flavour = bfd_get_flavour(abfd);
    dinfo->arch    = bfd_get_arch(abfd);
    dinfo->mach    = bfd_get_mach(abfd);
    dinfo->endian  = abfd->xvec->byteorder;
    disassemble_init_for_target(dinfo);
    return disassembler(abfd);
}
/*
 * Method of locating section from VMA taken from opdis.
 */
typedef struct {
    bfd_vma    vma;
    asection * sec;
} BFD_VMA_SECTION;
/*
 * Loads section and fills in dinfo accordingly. Since this function allocates
 * memory in dinfo->buffer, callers need to call free once they are finished.
 */
bool load_section(bfd * abfd, disassemble_info * dinfo, asection * s)
{
    int     size = bfd_section_size(s->owner, s);
    unsigned char * buf  = xmalloc(size);
    if(!bfd_get_section_contents(s->owner, s, buf, 0, size)) {
        free(buf);
        return FALSE;
    }
    dinfo->section       = s;
    dinfo->buffer        = buf;
    dinfo->buffer_length = size;
    dinfo->buffer_vma    = bfd_section_vma(s->owner, s);
    printf("Allocated %d bytes for %s section\n: 0x%lX", size, s->name,
            dinfo->buffer_vma);
    return TRUE;
}
/*
 * Used to locate section for a vma.
 */
void vma_in_section(bfd * abfd, asection * s, void * data)
{
    BFD_VMA_SECTION * req = data;
    if(req && req->vma >= s->vma &&
    req->vma < (s->vma + bfd_section_size(abfd, s)) ) {
        req->sec = s;
    }
}
/*
 * Locate and load section containing vma.
 */
bool load_section_for_vma(bfd * abfd, disassemble_info * dinfo,
        bfd_vma vma)
{
    BFD_VMA_SECTION req = {vma, NULL};
    bfd_map_over_sections(abfd, vma_in_section, &req);
    if(!req.sec) {
        return FALSE;
    } else {
        return load_section(abfd, dinfo, req.sec);
    }
}
/*
 * Start disassembling from entry point.
 */
bool disassemble_entry(bfd * abfd, disassemble_info * dinfo,
        disassembler_ftype disassembler)
{
    bfd_vma    vma = bfd_get_start_address(abfd);
    /* First locate and load the section containing the vma */
    if(load_section_for_vma(abfd, dinfo, vma)) {
        int size;
        /* Keep disassembling until signalled otherwise or error */
        while(true) {
            dinfo->insn_info_valid = 0;
            size = disassembler(vma, dinfo);
            printf("Disassembled %d bytes at 0x%lX\n", size, vma);
            if(size == 0 || size == -1 || stop_disassembling) {
                break;
            }
            vma += size;
        }
        free(dinfo->buffer);
        return TRUE;
    }
    return FALSE;
}
int main(void)
{
    char  target_path[PATH_MAX] = {0};
    bfd_init();
    /* Get path for the running instance of this program */
    get_target_path(target_path, ARRAY_SIZE(target_path));
    abfd = bfd_openr(target_path, NULL);
    if(abfd != NULL && bfd_check_format(abfd, bfd_object)) {
        disassembler_ftype disassembler = init_disasm(abfd, &dinfo);
        disassemble_entry(abfd, &dinfo, disassembler);
        bfd_close(abfd);
    }
    return EXIT_SUCCESS;
}

可以使用以下内容构建此源makefile。要执行成功的链接，binutils-dev需要将该软件包安装在本地计算机上：

all: gcc -Wall disasm.c -o disasm -lbfd -lopcodes clean: rm -f disasm

运行时，输出为：

Allocated 2216 bytes for .text section : 0x400BF0xor insn_info not valid %ebp insn_info not valid , insn_info not valid %ebp insn_info not valid Disassembled 2 bytes at 0x400BF0 mov insn_info not valid %rdx insn_info not valid , insn_info not valid %r9 insn_info not valid Disassembled 3 bytes at 0x400BF2 pop insn_info not valid %rsi insn_info not valid Disassembled 1 bytes at 0x400BF5 mov insn_info not valid %rsp insn_info not valid , insn_info not valid %rdx insn_info not valid Disassembled 3 bytes at 0x400BF6 and insn_info not valid $0xfffffffffffffff0 insn_info not valid , insn_info not valid %rsp insn_info not valid Disassembled 4 bytes at 0x400BF9 push insn_info not valid %rax insn_info not valid Disassembled 1 bytes at 0x400BFD push insn_info not valid %rsp insn_info not valid Disassembled 1 bytes at 0x400BFE mov insn_info not valid $0x401450 insn_info not valid , insn_info not valid %r8 insn_info not valid Disassembled 7 bytes at 0x400BFF mov insn_info not valid $0x4013c0 insn_info not valid , insn_info not valid %rcx insn_info not valid Disassembled 7 bytes at 0x400C06 mov insn_info not valid $0x4012ce insn_info not valid , insn_info not valid %rdi insn_info not valid Disassembled 7 bytes at 0x400C0D callq insn_info not valid 0x0000000000400ad8 insn_info not valid Disassembled 5 bytes at 0x400C14 hlt insn_info not valid Disassembled 1 bytes at 0x400C19 nop insn_info not valid Disassembled 1 bytes at 0x400C1A nop insn_info not valid Disassembled 1 bytes at 0x400C1B sub insn_info not valid $0x8 insn_info not valid , insn_info not valid %rsp insn_info not valid Disassembled 4 bytes at 0x400C1C mov insn_info not valid 0x2013b9(%rip) insn_info not valid , insn_info not valid %rax insn_info not valid # insn_info not valid 0x0000000000601fe0 insn_info not valid Disassembled 7 bytes at 0x400C20 test insn_info not valid %rax insn_info not valid , insn_info not valid %rax insn_info not valid Disassembled 3 bytes at 0x400C27 je insn_info not valid 0x0000000000400c2e insn_info not valid Disassembled 2 bytes at 0x400C2A callq insn_info not valid *%rax insn_info not valid Disassembled 2 bytes at 0x400C2C add insn_info not valid $0x8 insn_info not valid , insn_info not valid %rsp insn_info not valid Disassembled 4 bytes at 0x400C2E retq Stopped disassembly insn_info not valid Disassembled 1 bytes at 0x400C32

我所希望的是能够读取通过每个指令的指令信息dinfo->insn_type，target等等，行为展上双方的x86-32和x86-64。如果至少可以确认这两种架构上都没有实现，那么我可以自己填写此信息。