当我为android共享库编写自己的动态加载器时,我遇到了这样的问题:在库libnativeloader.so中有这样的plt条目android_init_namespaces @ plt,但是没有符号android_init_namespaces。我在仿生中找到了这样的代码:
LIBC {
global:
android_dlopen_ext;
dl_iterate_phdr;
dladdr;
dlclose;
dlerror;
dlopen;
dlsym;
local:
*;
};
LIBC_N {
global:
android_init_namespaces;
android_create_namespace;
dlvsym;
} LIBC;
LIBC_PLATFORM {
global:
android_get_application_target_sdk_version;
android_set_application_target_sdk_version;
android_get_LD_LIBRARY_PATH;
android_update_LD_LIBRARY_PATH;
} LIBC_N;
在这种情况下,似乎此符号位于libc.so中。但是libc.so中没有这样的符号。 有人可以帮忙解决这个问题吗?
答案 0 :(得分:0)
我猜你在谈论Android N.以下所有内容均基于这一假设。
这些符号不是来自任何共享库,它们在链接器中实现,并通过源代码中的手工soinfo
导出。
static ElfW(Sym) g_libdl_symtab[] = {
// Total length of libdl_info.strtab, including trailing 0.
// This is actually the STH_UNDEF entry. Technically, it's
// supposed to have st_name == 0, but instead, it points to an index
// in the strtab with a \0 to make iterating through the symtab easier.
ELFW(SYM_INITIALIZER)(sizeof(ANDROID_LIBDL_STRTAB) - 1, nullptr, 0),
ELFW(SYM_INITIALIZER)( 0, &dlopen, 1),
ELFW(SYM_INITIALIZER)( 7, &dlclose, 1),
ELFW(SYM_INITIALIZER)( 15, &dlsym, 1),
ELFW(SYM_INITIALIZER)( 21, &dlerror, 1),
ELFW(SYM_INITIALIZER)( 29, &dladdr, 1),
ELFW(SYM_INITIALIZER)( 36, &android_update_LD_LIBRARY_PATH, 1),
ELFW(SYM_INITIALIZER)( 67, &android_get_LD_LIBRARY_PATH, 1),
ELFW(SYM_INITIALIZER)( 95, &dl_iterate_phdr, 1),
ELFW(SYM_INITIALIZER)(111, &android_dlopen_ext, 1),
ELFW(SYM_INITIALIZER)(130, &android_set_application_target_sdk_version, 1),
ELFW(SYM_INITIALIZER)(173, &android_get_application_target_sdk_version, 1),
ELFW(SYM_INITIALIZER)(216, &android_init_namespaces, 1),
ELFW(SYM_INITIALIZER)(240, &android_create_namespace, 1),
ELFW(SYM_INITIALIZER)(265, &dlvsym, 1),
ELFW(SYM_INITIALIZER)(272, &android_dlwarning, 1),
#if defined(__arm__)
ELFW(SYM_INITIALIZER)(290, &dl_unwind_find_exidx, 1),
#endif
};
// This is used by the dynamic linker. Every process gets these symbols for free.
soinfo* get_libdl_info() {
if (__libdl_info == nullptr) {
__libdl_info = new (__libdl_info_buf) soinfo(&g_default_namespace, "libdl.so", nullptr, 0, RTLD_GLOBAL);
__libdl_info->flags_ |= FLAG_LINKED;
__libdl_info->strtab_ = ANDROID_LIBDL_STRTAB;
__libdl_info->symtab_ = g_libdl_symtab;
__libdl_info->nbucket_ = sizeof(g_libdl_buckets)/sizeof(unsigned);
__libdl_info->nchain_ = sizeof(g_libdl_chains)/sizeof(unsigned);
__libdl_info->bucket_ = g_libdl_buckets;
__libdl_info->chain_ = g_libdl_chains;
__libdl_info->ref_count_ = 1;
__libdl_info->strtab_size_ = sizeof(ANDROID_LIBDL_STRTAB);
__libdl_info->local_group_root_ = __libdl_info;
__libdl_info->soname_ = "libdl.so";
__libdl_info->target_sdk_version_ = __ANDROID_API__;
__libdl_info->generate_handle();
#if defined(__work_around_b_24465209__)
strlcpy(__libdl_info->old_name_, __libdl_info->soname_, sizeof(__libdl_info->old_name_));
#endif
}
检查https://android.googlesource.com/platform/bionic/+/android-7.0.0_r1/linker/dlfcn.cpp了解详情。