81 lines
1.9 KiB
C
81 lines
1.9 KiB
C
|
/*
|
||
|
|
* Test patching code, running in one thread, from another thread.
|
||
|
|
*
|
||
|
|
* Intel SDM calls this "cross-modifying code" and recommends a special
|
||
|
|
* sequence, which requires both threads to cooperate.
|
||
|
|
*
|
||
|
|
* Linux kernel uses a different sequence that does not require cooperation and
|
||
|
|
* involves patching the first byte with int3.
|
||
|
|
*
|
||
|
|
* Finally, there is user-mode software out there that simply uses atomics, and
|
||
|
|
* that seems to be good enough in practice. Test that QEMU has no problems
|
||
|
|
* with this as well.
|
||
|
|
*/
|
||
|
|
|
||
|
|
#include <assert.h>
|
||
|
|
#include <pthread.h>
|
||
|
|
#include <stdbool.h>
|
||
|
|
#include <stdlib.h>
|
||
|
|
|
||
|
|
void add1_or_nop(long *x);
|
||
|
|
asm(".pushsection .rwx,\"awx\",@progbits\n"
|
||
|
|
".globl add1_or_nop\n"
|
||
|
|
/* addq $0x1,(%rdi) */
|
||
|
|
"add1_or_nop: .byte 0x48, 0x83, 0x07, 0x01\n"
|
||
|
|
"ret\n"
|
||
|
|
".popsection\n");
|
||
|
|
|
||
|
|
#define THREAD_WAIT 0
|
||
|
|
#define THREAD_PATCH 1
|
||
|
|
#define THREAD_STOP 2
|
||
|
|
|
||
|
|
static void *thread_func(void *arg)
|
||
|
|
{
|
||
|
|
int val = 0x0026748d; /* nop */
|
||
|
|
|
||
|
|
while (true) {
|
||
|
|
switch (__atomic_load_n((int *)arg, __ATOMIC_SEQ_CST)) {
|
||
|
|
case THREAD_WAIT:
|
||
|
|
break;
|
||
|
|
case THREAD_PATCH:
|
||
|
|
val = __atomic_exchange_n((int *)&add1_or_nop, val,
|
||
|
|
__ATOMIC_SEQ_CST);
|
||
|
|
break;
|
||
|
|
case THREAD_STOP:
|
||
|
|
return NULL;
|
||
|
|
default:
|
||
|
|
assert(false);
|
||
|
|
__builtin_unreachable();
|
||
|
|
}
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
#define INITIAL 42
|
||
|
|
#define COUNT 1000000
|
||
|
|
|
||
|
|
int main(void)
|
||
|
|
{
|
||
|
|
int command = THREAD_WAIT;
|
||
|
|
pthread_t thread;
|
||
|
|
long x = 0;
|
||
|
|
int err;
|
||
|
|
int i;
|
||
|
|
|
||
|
|
err = pthread_create(&thread, NULL, &thread_func, &command);
|
||
|
|
assert(err == 0);
|
||
|
|
|
||
|
|
__atomic_store_n(&command, THREAD_PATCH, __ATOMIC_SEQ_CST);
|
||
|
|
for (i = 0; i < COUNT; i++) {
|
||
|
|
add1_or_nop(&x);
|
||
|
|
}
|
||
|
|
__atomic_store_n(&command, THREAD_STOP, __ATOMIC_SEQ_CST);
|
||
|
|
|
||
|
|
err = pthread_join(thread, NULL);
|
||
|
|
assert(err == 0);
|
||
|
|
|
||
|
|
assert(x >= INITIAL);
|
||
|
|
assert(x <= INITIAL + COUNT);
|
||
|
|
|
||
|
|
return EXIT_SUCCESS;
|
||
|
|
}
|