linker: Make the errors reported by dlopen/dlsym be more useful.
Changed it so that when the linker generates error messages, they are
scribbled away into a buffer that dlfcn and friends can read from.
Since the error messages are generetad with snprintf, and snprintf
MAY call malloc during some code paths, we now link against a version
of libc that does not contain malloc/free/realloc/calloc. We then define
malloc and friends in the dynamic loader, and make them abort() if they
are ever called.
Signed-off-by: Dima Zavin <dima@android.com>
diff --git a/linker/dlfcn.c b/linker/dlfcn.c
index cd73d11..b54674f 100644
--- a/linker/dlfcn.c
+++ b/linker/dlfcn.c
@@ -15,41 +15,49 @@
*/
#include <dlfcn.h>
#include <pthread.h>
+#include <stdio.h>
#include "linker.h"
/* This file hijacks the symbols stubbed out in libdl.so. */
#define DL_SUCCESS 0
-#define DL_ERR_CANNOT_FIND_LIBRARY 1
+#define DL_ERR_CANNOT_LOAD_LIBRARY 1
#define DL_ERR_INVALID_LIBRARY_HANDLE 2
#define DL_ERR_BAD_SYMBOL_NAME 3
#define DL_ERR_SYMBOL_NOT_FOUND 4
#define DL_ERR_SYMBOL_NOT_GLOBAL 5
+static char dl_err_buf[1024];
+static const char *dl_err_str;
+
static const char *dl_errors[] = {
- [DL_SUCCESS] = NULL,
- [DL_ERR_CANNOT_FIND_LIBRARY] = "Cannot find library",
+ [DL_ERR_CANNOT_LOAD_LIBRARY] = "Cannot load library",
[DL_ERR_INVALID_LIBRARY_HANDLE] = "Invalid library handle",
[DL_ERR_BAD_SYMBOL_NAME] = "Invalid symbol name",
[DL_ERR_SYMBOL_NOT_FOUND] = "Symbol not found",
[DL_ERR_SYMBOL_NOT_GLOBAL] = "Symbol is not global",
};
-static int dl_last_err = DL_SUCCESS;
-
#define likely(expr) __builtin_expect (expr, 1)
#define unlikely(expr) __builtin_expect (expr, 0)
static pthread_mutex_t dl_lock = PTHREAD_MUTEX_INITIALIZER;
-void *dlopen(const char *filename, int flag)
+static void set_dlerror(int err)
+{
+ snprintf(dl_err_buf, sizeof(dl_err_buf), "%s: %s", dl_errors[err],
+ linker_get_error());
+ dl_err_str = (const char *)&dl_err_buf[0];
+};
+
+void *dlopen(const char *filename, int flag)
{
soinfo *ret;
pthread_mutex_lock(&dl_lock);
ret = find_library(filename);
if (unlikely(ret == NULL)) {
- dl_last_err = DL_ERR_CANNOT_FIND_LIBRARY;
+ set_dlerror(DL_ERR_CANNOT_LOAD_LIBRARY);
} else {
ret->refcount++;
}
@@ -59,9 +67,9 @@
const char *dlerror(void)
{
- const char *err = dl_errors[dl_last_err];
- dl_last_err = DL_SUCCESS;
- return err;
+ const char *tmp = dl_err_str;
+ dl_err_str = NULL;
+ return (const char *)tmp;
}
void *dlsym(void *handle, const char *symbol)
@@ -71,16 +79,16 @@
unsigned bind;
pthread_mutex_lock(&dl_lock);
-
+
if(unlikely(handle == 0)) {
- dl_last_err = DL_ERR_INVALID_LIBRARY_HANDLE;
+ set_dlerror(DL_ERR_INVALID_LIBRARY_HANDLE);
goto err;
}
if(unlikely(symbol == 0)) {
- dl_last_err = DL_ERR_BAD_SYMBOL_NAME;
+ set_dlerror(DL_ERR_BAD_SYMBOL_NAME);
goto err;
}
-
+
if(handle == RTLD_DEFAULT) {
sym = lookup(symbol, &base);
} else if(handle == RTLD_NEXT) {
@@ -92,16 +100,17 @@
if(likely(sym != 0)) {
bind = ELF32_ST_BIND(sym->st_info);
-
+
if(likely((bind == STB_GLOBAL) && (sym->st_shndx != 0))) {
unsigned ret = sym->st_value + base;
pthread_mutex_unlock(&dl_lock);
return (void*)ret;
}
- dl_last_err = DL_ERR_SYMBOL_NOT_GLOBAL;
+ set_dlerror(DL_ERR_SYMBOL_NOT_GLOBAL);
}
- else dl_last_err = DL_ERR_SYMBOL_NOT_FOUND;
+ else
+ set_dlerror(DL_ERR_SYMBOL_NOT_FOUND);
err:
pthread_mutex_unlock(&dl_lock);