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use an accessor function for __libc data pointer when compiled as PIC

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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.
This commit is contained in:
Rich Felker
2011-02-20 22:30:06 -05:00
parent 4ee039f354
commit d89c9e8a63
2 changed files with 19 additions and 4 deletions
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10
src/internal/libc.c
View File

@ -1,3 +1,11 @@
#include "libc.h" #include "libc.h"
struct libc libc; #ifdef __PIC__
struct __libc *__libc_loc()
{
static struct __libc __libc;
return &__libc;
}
#else
struct __libc __libc;
#endif

13
src/internal/libc.h
View File

@ -4,8 +4,7 @@
#include <stdlib.h> #include <stdlib.h>
#include <stdio.h> #include <stdio.h>
#define libc __libc struct __libc {
extern struct libc {
void (*lock)(volatile int *); void (*lock)(volatile int *);
void (*cancelpt)(int); void (*cancelpt)(int);
int (*atexit)(void (*)(void)); int (*atexit)(void (*)(void));
@ -16,7 +15,15 @@ extern struct libc {
int (*rsyscall)(int, long, long, long, long, long, long); int (*rsyscall)(int, long, long, long, long, long, long);
void (**tsd_keys)(void *); void (**tsd_keys)(void *);
void (*fork_handler)(int); 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 */ /* Designed to avoid any overhead in non-threaded processes */