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/* Copyright The GNU Toolchain Authors. */
#include <unistd.h>
#include <sys/mman.h>
#include <stdint.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#if __APPLE__ && __ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__ >= 101400
/* For pthread_jit_write_protect_np */
#include <pthread.h>
#endif
void *allocate_trampoline_page (void);
int get_trampolines_per_page (void);
struct tramp_ctrl_data *allocate_tramp_ctrl (struct tramp_ctrl_data *parent);
void *allocate_trampoline_page (void);
void __builtin_nested_func_ptr_created (void *chain, void *func, void **dst);
void __builtin_nested_func_ptr_deleted (void);
static const uint8_t trampoline_insns[] = {
/* movabs $<chain>,%r11 */
0x49, 0xbb,
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
/* movabs $<func>,%r10 */
0x49, 0xba,
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
/* rex.WB jmpq *%r11 */
0x41, 0xff, 0xe3
};
union ix86_trampoline {
uint8_t insns[sizeof(trampoline_insns)];
struct __attribute__((packed)) fields {
uint8_t insn_0[2];
void *func_ptr;
uint8_t insn_1[2];
void *chain_ptr;
uint8_t insn_2[3];
} fields;
};
struct tramp_ctrl_data
{
struct tramp_ctrl_data *prev;
int free_trampolines;
/* This will be pointing to an executable mmap'ed page. */
union ix86_trampoline *trampolines;
};
int
get_trampolines_per_page (void)
{
return getpagesize() / sizeof(union ix86_trampoline);
}
static _Thread_local struct tramp_ctrl_data *tramp_ctrl_curr = NULL;
void *
allocate_trampoline_page (void)
{
void *page;
#if defined(__gnu_linux__)
page = mmap (0, getpagesize (), PROT_WRITE | PROT_EXEC,
MAP_ANON | MAP_PRIVATE, 0, 0);
#elif __APPLE__
# if __ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__ >= 101400
page = mmap (0, getpagesize (), PROT_WRITE | PROT_EXEC,
MAP_ANON | MAP_PRIVATE | MAP_JIT, 0, 0);
# else
page = mmap (0, getpagesize (), PROT_WRITE | PROT_EXEC,
MAP_ANON | MAP_PRIVATE, 0, 0);
# endif
#else
page = MAP_FAILED;
#endif
return page;
}
struct tramp_ctrl_data *
allocate_tramp_ctrl (struct tramp_ctrl_data *parent)
{
struct tramp_ctrl_data *p = malloc (sizeof (struct tramp_ctrl_data));
if (p == NULL)
return NULL;
p->trampolines = allocate_trampoline_page ();
if (p->trampolines == MAP_FAILED)
return NULL;
p->prev = parent;
p->free_trampolines = get_trampolines_per_page();
return p;
}
void
__builtin_nested_func_ptr_created (void *chain, void *func, void **dst)
{
if (tramp_ctrl_curr == NULL)
{
tramp_ctrl_curr = allocate_tramp_ctrl (NULL);
if (tramp_ctrl_curr == NULL)
abort ();
}
if (tramp_ctrl_curr->free_trampolines == 0)
{
void *tramp_ctrl = allocate_tramp_ctrl (tramp_ctrl_curr);
if (!tramp_ctrl)
abort ();
tramp_ctrl_curr = tramp_ctrl;
}
union ix86_trampoline *trampoline
= &tramp_ctrl_curr->trampolines[get_trampolines_per_page ()
- tramp_ctrl_curr->free_trampolines];
#if __APPLE__ && __ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__ >= 101400
/* Disable write protection for the MAP_JIT regions in this thread (see
https://developer.apple.com/documentation/apple-silicon/porting-just-in-time-compilers-to-apple-silicon) */
pthread_jit_write_protect_np (0);
#endif
memcpy (trampoline->insns, trampoline_insns,
sizeof(trampoline_insns));
trampoline->fields.func_ptr = func;
trampoline->fields.chain_ptr = chain;
#if __APPLE__ && __ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__ >= 101400
/* Re-enable write protection. */
pthread_jit_write_protect_np (1);
#endif
tramp_ctrl_curr->free_trampolines -= 1;
__builtin___clear_cache ((void *)trampoline->insns,
((void *)trampoline->insns + sizeof(trampoline->insns)));
*dst = &trampoline->insns;
}
void
__builtin_nested_func_ptr_deleted (void)
{
if (tramp_ctrl_curr == NULL)
abort ();
tramp_ctrl_curr->free_trampolines += 1;
if (tramp_ctrl_curr->free_trampolines == get_trampolines_per_page ())
{
if (tramp_ctrl_curr->prev == NULL)
return;
munmap (tramp_ctrl_curr->trampolines, getpagesize());
struct tramp_ctrl_data *prev = tramp_ctrl_curr->prev;
free (tramp_ctrl_curr);
tramp_ctrl_curr = prev;
}
}
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