我正在寻找一个c库/框架,它允许我替换内存中的函数并将它们重定向到我自己的实现,同时仍然允许我的实现调用原始实现。
这在linux-y系统上似乎是一个相当罕见的需求,可能是因为ld_preload涵盖了运行时函数替换thingies的大部分方面。
最佳答案
下面的方法似乎适用于我的应用程序。我不喜欢我的机器上有专利的斑点,所以我不知道它是否和蒸汽一起工作。不过,我很想知道,我看不出为什么不应该。
以下方法使用_dl_vsym()
在执行dlsym()
之前从dlvsym()
中查找正确版本的libdl.so
和main()
。在应用程序执行期间,插入的dlsym()
和dlvsym()
调用它们的原始版本(而不是_dl_vsym()
);我认为这应该避免任何特定于应用程序的问题。
如果其他动态库在此之前初始化,则使用这些函数的非常小心的初始版本。它们使用_dl_vsym()
获取对libdldlsym()
或dlvsym()
函数的引用;任何后续调用都将使用libdldlsym()
或dlvsym()
。这将脆弱的时间限制在库初始化期间的第一次调用,但是优先级101希望首先初始化这个库。
#define _GNU_SOURCE
#include <dlfcn.h>
#include <errno.h>
#include <string.h>
#include <GL/glx.h>
#include <EGL/egl.h>
#define UNUSED __attribute__((unused))
#define LIBDL_VERSION "GLIBC_2.2.5"
#define LIBDL_PATH "libdl.so"
extern void *_dl_vsym(void *, const char *, const char *, void *);
static const struct {
const char *const symbol;
const char *const version;
void *const function;
} interposed[] = {
{ "dlsym", LIBDL_VERSION, dlsym },
{ "dlvsym", LIBDL_VERSION, dlvsym },
{ "glXSwapBuffers", (const char *)0, glXSwapBuffers },
{ "eglSwapBuffers", (const char *)0, eglSwapBuffers },
{ (const char *)0, (const char *)0, (void *)0 }
};
static void * initial_dlsym(void *, const char *);
static void * initial_dlvsym(void *, const char *, const char *);
static void initial_glXSwapBuffers(Display *, GLXDrawable);
static EGLBoolean initial_eglSwapBuffers(EGLDisplay, EGLSurface);
static void * (*actual_dlsym)(void *, const char *) = initial_dlsym;
static void * (*actual_dlvsym)(void *, const char *, const char *) = initial_dlvsym;
static void (*actual_glXSwapBuffers)(Display *, GLXDrawable) = initial_glXSwapBuffers;
static EGLBoolean (*actual_eglSwapBuffers)(EGLDisplay, EGLSurface) = initial_eglSwapBuffers;
static void initial_glXSwapBuffers(Display *display UNUSED, GLXDrawable drawable UNUSED)
{
return;
}
static EGLBoolean initial_eglSwapBuffers(EGLDisplay display UNUSED, EGLSurface surface UNUSED)
{
return 0;
}
static void *initial_dlsym(void *handle, const char *const symbol)
{
void *(*call_dlsym)(void *, const char *);
if (symbol) {
size_t i;
for (i = 0; interposed[i].symbol; i++)
if (!strcmp(symbol, interposed[i].symbol))
return interposed[i].function;
}
*(void **)(&call_dlsym) = __atomic_load_n((void **)(&actual_dlsym), __ATOMIC_SEQ_CST);
if (!call_dlsym || call_dlsym == initial_dlsym) {
const int saved_errno = errno;
void *handle;
handle = dlopen(LIBDL_PATH, RTLD_NOW | RTLD_LOCAL | RTLD_DEEPBIND | RTLD_NODELETE);
call_dlsym = _dl_vsym(handle, "dlsym", LIBDL_VERSION, dlsym);
dlclose(handle);
if (!call_dlsym || call_dlsym == initial_dlsym || call_dlsym == dlsym) {
errno = saved_errno;
return (void *)0;
}
__atomic_store_n((void **)(&actual_dlsym), call_dlsym, __ATOMIC_SEQ_CST);
errno = saved_errno;
}
return call_dlsym(handle, symbol);
}
static void *initial_dlvsym(void *handle, const char *const symbol, const char *const version)
{
void *(*call_dlvsym)(void *, const char *, const char *);
if (symbol) {
size_t i;
for (i = 0; interposed[i].symbol; i++)
if (!strcmp(symbol, interposed[i].symbol))
if (!interposed[i].version || !version || !strcmp(version, interposed[i].version))
return interposed[i].function;
}
*(void **)(&call_dlvsym) = __atomic_load_n((void **)(&actual_dlvsym), __ATOMIC_SEQ_CST);
if (!call_dlvsym || call_dlvsym == initial_dlvsym) {
const int saved_errno = errno;
void *handle;
handle = dlopen(LIBDL_PATH, RTLD_NOW | RTLD_LOCAL | RTLD_DEEPBIND | RTLD_NODELETE);
call_dlvsym = _dl_vsym(handle, "dlvsym", LIBDL_VERSION, dlvsym);
dlclose(handle);
if (!call_dlvsym || call_dlvsym == initial_dlvsym || call_dlvsym == dlvsym) {
errno = saved_errno;
return (void *)0;
}
__atomic_store_n((void **)(&actual_dlvsym), call_dlvsym, __ATOMIC_SEQ_CST);
errno = saved_errno;
}
return call_dlvsym(handle, symbol, version);
}
void *dlsym(void *handle, const char *const symbol)
{
if (symbol) {
size_t i;
for (i = 0; interposed[i].symbol; i++)
if (!strcmp(symbol, interposed[i].symbol))
return interposed[i].function;
}
return actual_dlsym(handle, symbol);
}
void *dlvsym(void *handle, const char *const symbol, const char *version)
{
if (symbol) {
size_t i;
for (i = 0; interposed[i].symbol; i++)
if (!strcmp(symbol, interposed[i].symbol))
if (!interposed[i].version || !version || !strcmp(version, interposed[i].version))
return interposed[i].function;
}
return actual_dlvsym(handle, symbol, version);
}
static void init(void) __attribute__((constructor (101)));
static void init(void)
{
int saved_errno;
void *handle;
saved_errno = errno;
handle = dlopen(LIBDL_PATH, RTLD_NOW | RTLD_LOCAL | RTLD_DEEPBIND | RTLD_NODELETE);
__atomic_store_n((void **)(&actual_dlsym), _dl_vsym(handle, "dlsym", LIBDL_VERSION, dlsym), __ATOMIC_SEQ_CST);
__atomic_store_n((void **)(&actual_dlvsym), _dl_vsym(handle, "dlvsym", LIBDL_VERSION, dlvsym), __ATOMIC_SEQ_CST);
dlclose(handle);
__atomic_store_n((void **)(&actual_glXSwapBuffers), actual_dlsym(RTLD_NEXT, "glXSwapBuffers"), __ATOMIC_SEQ_CST);
__atomic_store_n((void **)(&actual_eglSwapBuffers), actual_dlsym(RTLD_NEXT, "eglSwapBuffers"), __ATOMIC_SEQ_CST);
errno = saved_errno;
}
void glXSwapBuffers(Display *dpy, GLXDrawable drawable)
{
/* TODO: Custom stuff before glXSwapBuffers() */
actual_glXSwapBuffers(dpy, drawable);
/* TODO: Custom stuff after glXSwapBuffers() */
}
EGLBoolean eglSwapBuffers(EGLDisplay dpy, EGLSurface surface)
{
EGLBoolean result;
/* TODO: Custom stuff before eglSwapBuffers() */
result = actual_eglSwapBuffers(dpy, surface);
/* TODO: Custom stuff after eglSwapBuffers() */
return result;
}
如果将上面的代码保存为
example.c
,则可以使用gcc -Wall -fPIC -shared `pkg-config --cflags gl egl` example.c -ldl -Wl,-soname,libexample.so `pkg-config --libs gl egl` -o libexample.so
在某些情况下,您需要修改
libexample.so
。使用find /lib* /usr/ -name 'libdl.*' | while read FILE ; do echo "$FILE:" ; readelf -s "$FILE" | sed -ne '/ dlsym@/ s|^.*@@*|\t|p' ; done
检查libdl使用的api版本。(我看到过
LIBDL_VERSION
和GLIBC_2.0
;它并不反映库的实际版本,而是GLIBC_2.2.5
和dlsym()
调用的api版本。)dlvsym()
数组包含插入函数的修改结果。我已经验证了上面的示例不会与我尝试过的任何应用程序(包括我编写的一个简单的
interposed[]
和dlsym()
压力测试)崩溃,并且它也正确地插入了dlvsym()
(在glXSwapBuffers()
和glxgears
中)。问题?评论?
关于c - Hook 框架(类似于Detours),我们在Stack Overflow上找到一个类似的问题:https://stackoverflow.com/questions/26897350/