tcc_load_dll

在遇到-lc这样的参数时, 如果可能，会尽量选择动态库
如下函数加载一个动态库, 　文件已经打开

/* load a DLL and all referenced DLLs. 'level = 0' means that the DLL
   is referenced by the user (so it should be added as DT_NEEDED in
   the generated ELF file) */
ST_FUNC int tcc_load_dll(TCCState *s1, int fd, const char *filename, int level)
{//
    ElfW(Ehdr) ehdr;
    ElfW(Shdr) *shdr, *sh, *sh1;
    int i, j, nb_syms, nb_dts, sym_bind, ret;
    ElfW(Sym) *sym, *dynsym;
    ElfW(Dyn) *dt, *dynamic;
    unsigned char *dynstr;
    const char *name, *soname;
    DLLReference *dllref;

    read(fd, &ehdr, sizeof(ehdr));

    /* test CPU specific stuff */
    if (ehdr.e_ident[5] != ELFDATA2LSB ||
        ehdr.e_machine != EM_TCC_TARGET) {
        error_noabort("bad architecture");
        return -1;
    }

    /* read sections */
    shdr = load_data(fd, ehdr.e_shoff, sizeof(ElfW(Shdr)) * ehdr.e_shnum);

    /* load dynamic section and dynamic symbols */
    nb_syms = 0;
    nb_dts = 0;
    dynamic = NULL;
    dynsym = NULL; /* avoid warning */
    dynstr = NULL; /* avoid warning */
    for(i = 0, sh = shdr; i < ehdr.e_shnum; i++, sh++) {
        switch(sh->sh_type) {
        case SHT_DYNAMIC:
            nb_dts = sh->sh_size / sizeof(ElfW(Dyn));
            dynamic = load_data(fd, sh->sh_offset, sh->sh_size);
            break;
        case SHT_DYNSYM:
            nb_syms = sh->sh_size / sizeof(ElfW(Sym));
            dynsym = load_data(fd, sh->sh_offset, sh->sh_size);
            sh1 = &shdr[sh->sh_link];
            dynstr = load_data(fd, sh1->sh_offset, sh1->sh_size);
            break;
        default:
            break;
        }
    }
    soname通常和文件名一样，但是如果不一样，内部解决依赖会以内部名字为主

     比如把libm复制到当前目录, export LD_LIBRARY_PATH=.
     mv libm.so.6 liba.so

xcm@u32:~/study/tinycc$ tcc t.c -L. -la
xcm@u32:~/study/tinycc$ ldd a.out
    linux-gate.so.1 =>  (0xb77c6000)
    libm.so.6 => /lib/tls/i686/cmov/libm.so.6 (0xb778c000) 仍然找libm.so.6，因为liba的soname是它
    libc.so.6 => /lib/tls/i686/cmov/libc.so.6 (0xb7632000)
    /lib/ld-linux.so.2 (0xb77c7000)
xcm@u32:~/study/tinycc$ mv liba.so libm.so
xcm@u32:~/study/tinycc$ ldd a.out
    linux-gate.so.1 =>  (0xb78a4000)
    libm.so.6 => /lib/tls/i686/cmov/libm.so.6 (0xb786a000)　同样
    libc.so.6 => /lib/tls/i686/cmov/libc.so.6 (0xb7710000)
    /lib/ld-linux.so.2 (0xb78a5000)
xcm@u32:~/study/tinycc$ mv libm.so libm.so.6
xcm@u32:~/study/tinycc$ ldd a.out
    linux-gate.so.1 =>  (0xb7757000)
    libm.so.6 => ./libm.so.6 (0xb772f000)　这个时候就对了
    libc.so.6 => /lib/tls/i686/cmov/libc.so.6 (0xb75c3000)
    /lib/ld-linux.so.2 (0xb7758000)
           

    /* compute the real library name */
    soname = tcc_basename(filename);

    for(i = 0, dt = dynamic; i < nb_dts; i++, dt++) {
        if (dt->d_tag == DT_SONAME) {
            soname = dynstr + dt->d_un.d_val;
        }
    }

    /* if the dll is already loaded, do not load it */
    for(i = 0; i < s1->nb_loaded_dlls; i++) {
        dllref = s1->loaded_dlls[i];
        if (!strcmp(soname, dllref->name)) {
            /* but update level if needed */
            if (level < dllref->level)
                dllref->level = level;
            ret = 0;
            goto the_end;
        }
    }

    //    printf("loading dll '%s'\n", soname);

    /* add the dll and its level */
    dllref = tcc_mallocz(sizeof(DLLReference) + strlen(soname));
    dllref->level = level;
    strcpy(dllref->name, soname);
    dynarray_add((void ***)&s1->loaded_dlls, &s1->nb_loaded_dlls, dllref);

    /* add dynamic symbols in dynsym_section */
    for(i = 1, sym = dynsym + 1; i < nb_syms; i++, sym++) {
        sym_bind = ELFW(ST_BIND)(sym->st_info);
        if (sym_bind == STB_LOCAL)
            continue;
        name = dynstr + sym->st_name;
　　　　　ｏｋ，　该符号可用了
        add_elf_sym(s1->dynsymtab_section, sym->st_value, sym->st_size,
                    sym->st_info, sym->st_other, sym->st_shndx, name);
    }
　　　查找依赖
    /* load all referenced DLLs */
    for(i = 0, dt = dynamic; i < nb_dts; i++, dt++) {
        switch(dt->d_tag) {
        case DT_NEEDED:
            name = dynstr + dt->d_un.d_val;
            for(j = 0; j < s1->nb_loaded_dlls; j++) {
                dllref = s1->loaded_dlls[j];
                if (!strcmp(name, dllref->name))
                    goto already_loaded;
            }
            if (tcc_add_dll(s1, name, AFF_REFERENCED_DLL) < 0) {
                error_noabort("referenced dll '%s' not found", name);
                ret = -1;
                goto the_end;
            }
        already_loaded:
            break;
        }
    }
    ret = 0;
 the_end:
    tcc_free(dynstr);
    tcc_free(dynsym);
    tcc_free(dynamic);
    tcc_free(shdr);
    return ret;
}