Simplify iOS trampoline table allocation
By using VM_FLAGS_OVERWRITE there is no need for speculatively
allocating on a page we just deallocated. This approach eliminates the
race-condition and gets rid of the retry logic.
diff --git a/src/closures.c b/src/closures.c
index 78d6aeb..f7eb464 100644
--- a/src/closures.c
+++ b/src/closures.c
@@ -107,93 +107,83 @@
static ffi_trampoline_table *ffi_trampoline_tables = NULL;
static ffi_trampoline_table *
-ffi_trampoline_table_alloc ()
+ffi_trampoline_table_alloc (void)
{
- ffi_trampoline_table *table = NULL;
+ ffi_trampoline_table *table;
+ vm_address_t config_page;
+ vm_address_t trampoline_page;
+ vm_address_t trampoline_page_template;
+ vm_prot_t cur_prot;
+ vm_prot_t max_prot;
+ kern_return_t kt;
+ uint16_t i;
- /* Loop until we can allocate two contiguous pages */
- while (table == NULL)
- {
- vm_address_t config_page = 0x0;
- kern_return_t kt;
+ /* Allocate two pages -- a config page and a placeholder page */
+ config_page = 0x0;
+ kt = vm_allocate (mach_task_self (), &config_page, PAGE_MAX_SIZE * 2,
+ VM_FLAGS_ANYWHERE);
+ if (kt != KERN_SUCCESS)
+ return NULL;
- /* Try to allocate two pages */
- kt =
- vm_allocate (mach_task_self (), &config_page, PAGE_MAX_SIZE * 2,
- VM_FLAGS_ANYWHERE);
- if (kt != KERN_SUCCESS)
- {
- fprintf (stderr, "vm_allocate() failure: %d at %s:%d\n", kt,
- __FILE__, __LINE__);
- break;
- }
-
- /* Now drop the second half of the allocation to make room for the trampoline table */
- vm_address_t trampoline_page = config_page + PAGE_MAX_SIZE;
- kt = vm_deallocate (mach_task_self (), trampoline_page, PAGE_MAX_SIZE);
- if (kt != KERN_SUCCESS)
- {
- fprintf (stderr, "vm_deallocate() failure: %d at %s:%d\n", kt,
- __FILE__, __LINE__);
- break;
- }
-
- /* Remap the trampoline table to directly follow the config page */
- vm_prot_t cur_prot;
- vm_prot_t max_prot;
-
- vm_address_t trampoline_page_template = (vm_address_t)&ffi_closure_trampoline_table_page;
+ /* Remap the trampoline table on top of the placeholder page */
+ trampoline_page = config_page + PAGE_MAX_SIZE;
+ trampoline_page_template = (vm_address_t)&ffi_closure_trampoline_table_page;
#ifdef __arm__
- /* ffi_closure_trampoline_table_page can be thumb-biased on some ARM archs */
- trampoline_page_template &= ~1UL;
+ /* ffi_closure_trampoline_table_page can be thumb-biased on some ARM archs */
+ trampoline_page_template &= ~1UL;
#endif
-
- kt =
- vm_remap (mach_task_self (), &trampoline_page, PAGE_MAX_SIZE, 0x0, FALSE,
- mach_task_self (), trampoline_page_template, FALSE,
- &cur_prot, &max_prot, VM_INHERIT_SHARE);
-
- /* If we lost access to the destination trampoline page, drop our config allocation mapping and retry */
- if (kt != KERN_SUCCESS)
- {
- /* Log unexpected failures */
- if (kt != KERN_NO_SPACE)
- {
- fprintf (stderr, "vm_remap() failure: %d at %s:%d\n", kt,
- __FILE__, __LINE__);
- }
-
- vm_deallocate (mach_task_self (), config_page, PAGE_SIZE);
- continue;
- }
-
- /* We have valid trampoline and config pages */
- table = calloc (1, sizeof (ffi_trampoline_table));
- table->free_count = FFI_TRAMPOLINE_COUNT;
- table->config_page = config_page;
- table->trampoline_page = trampoline_page;
-
- /* Create and initialize the free list */
- table->free_list_pool =
- calloc (FFI_TRAMPOLINE_COUNT, sizeof (ffi_trampoline_table_entry));
-
- uint16_t i;
- for (i = 0; i < table->free_count; i++)
- {
- ffi_trampoline_table_entry *entry = &table->free_list_pool[i];
- entry->trampoline =
- (void *) (table->trampoline_page + (i * FFI_TRAMPOLINE_SIZE));
-
- if (i < table->free_count - 1)
- entry->next = &table->free_list_pool[i + 1];
- }
-
- table->free_list = table->free_list_pool;
+ kt = vm_remap (mach_task_self (), &trampoline_page, PAGE_MAX_SIZE, 0x0,
+ VM_FLAGS_OVERWRITE, mach_task_self (), trampoline_page_template,
+ FALSE, &cur_prot, &max_prot, VM_INHERIT_SHARE);
+ if (kt != KERN_SUCCESS)
+ {
+ vm_deallocate (mach_task_self (), config_page, PAGE_MAX_SIZE * 2);
+ return NULL;
}
+ /* We have valid trampoline and config pages */
+ table = calloc (1, sizeof (ffi_trampoline_table));
+ table->free_count = FFI_TRAMPOLINE_COUNT;
+ table->config_page = config_page;
+ table->trampoline_page = trampoline_page;
+
+ /* Create and initialize the free list */
+ table->free_list_pool =
+ calloc (FFI_TRAMPOLINE_COUNT, sizeof (ffi_trampoline_table_entry));
+
+ for (i = 0; i < table->free_count; i++)
+ {
+ ffi_trampoline_table_entry *entry = &table->free_list_pool[i];
+ entry->trampoline =
+ (void *) (table->trampoline_page + (i * FFI_TRAMPOLINE_SIZE));
+
+ if (i < table->free_count - 1)
+ entry->next = &table->free_list_pool[i + 1];
+ }
+
+ table->free_list = table->free_list_pool;
+
return table;
}
+static void
+ffi_trampoline_table_free (ffi_trampoline_table *table)
+{
+ /* Remove from the list */
+ if (table->prev != NULL)
+ table->prev->next = table->next;
+
+ if (table->next != NULL)
+ table->next->prev = table->prev;
+
+ /* Deallocate pages */
+ vm_deallocate (mach_task_self (), table->config_page, PAGE_MAX_SIZE * 2);
+
+ /* Deallocate free list */
+ free (table->free_list_pool);
+ free (table);
+}
+
void *
ffi_closure_alloc (size_t size, void **code)
{
@@ -261,29 +251,7 @@
if (table->free_count == FFI_TRAMPOLINE_COUNT
&& ffi_trampoline_tables != table)
{
- /* Remove from the list */
- if (table->prev != NULL)
- table->prev->next = table->next;
-
- if (table->next != NULL)
- table->next->prev = table->prev;
-
- /* Deallocate pages */
- kern_return_t kt;
- kt = vm_deallocate (mach_task_self (), table->config_page, PAGE_SIZE);
- if (kt != KERN_SUCCESS)
- fprintf (stderr, "vm_deallocate() failure: %d at %s:%d\n", kt,
- __FILE__, __LINE__);
-
- kt =
- vm_deallocate (mach_task_self (), table->trampoline_page, PAGE_SIZE);
- if (kt != KERN_SUCCESS)
- fprintf (stderr, "vm_deallocate() failure: %d at %s:%d\n", kt,
- __FILE__, __LINE__);
-
- /* Deallocate free list */
- free (table->free_list_pool);
- free (table);
+ ffi_trampoline_table_free (table);
}
else if (ffi_trampoline_tables != table)
{
