prior to this change, a large portion of libc was unusable prior to
relocation by the dynamic linker, due to dependence on the global data
in the __libc structure and the need to obtain its address through the
GOT. with this patch, the accessor function __libc_loc is now able to
obtain the address of __libc via PC-relative addressing without using
the GOT. this means the majority of libc functionality is now
accessible right away.
naturally, the above statements all depend on having an architecture
where PC-relative addressing and jumps/calls are feasible, and a
compiler that generates the appropriate code.
#include "libc.h"
-struct libc libc;
+#ifdef __PIC__
+struct __libc *__libc_loc()
+{
+ static struct __libc __libc;
+ return &__libc;
+}
+#else
+struct __libc __libc;
+#endif
#include <stdlib.h>
#include <stdio.h>
-#define libc __libc
-extern struct libc {
+struct __libc {
void (*lock)(volatile int *);
void (*cancelpt)(int);
int (*atexit)(void (*)(void));
int (*rsyscall)(int, long, long, long, long, long, long);
void (**tsd_keys)(void *);
void (*fork_handler)(int);
-} libc;
+};
+
+#ifdef __PIC__
+extern struct __libc *__libc_loc(void) __attribute__((const));
+#define libc (*__libc_loc())
+#else
+extern struct __libc __libc;
+#define libc __libc
+#endif
/* Designed to avoid any overhead in non-threaded processes */