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.
This commit is contained in:
Ole André Vadla Ravnås
committed by
ksjogo
ksjogo
parent
7f558a9ba4
commit
57d8ff044c
168
src/closures.c
168
src/closures.c
@@ -107,93 +107,83 @@ static pthread_mutex_t ffi_trampoline_lock = PTHREAD_MUTEX_INITIALIZER;
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static ffi_trampoline_table *ffi_trampoline_tables = NULL;
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static ffi_trampoline_table *
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ffi_trampoline_table_alloc ()
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ffi_trampoline_table_alloc (void)
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{
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ffi_trampoline_table *table = NULL;
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ffi_trampoline_table *table;
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vm_address_t config_page;
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vm_address_t trampoline_page;
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vm_address_t trampoline_page_template;
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vm_prot_t cur_prot;
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vm_prot_t max_prot;
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kern_return_t kt;
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uint16_t i;
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/* Loop until we can allocate two contiguous pages */
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while (table == NULL)
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{
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vm_address_t config_page = 0x0;
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kern_return_t kt;
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/* Allocate two pages -- a config page and a placeholder page */
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config_page = 0x0;
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kt = vm_allocate (mach_task_self (), &config_page, PAGE_MAX_SIZE * 2,
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VM_FLAGS_ANYWHERE);
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if (kt != KERN_SUCCESS)
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return NULL;
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/* Try to allocate two pages */
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kt =
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vm_allocate (mach_task_self (), &config_page, PAGE_MAX_SIZE * 2,
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VM_FLAGS_ANYWHERE);
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if (kt != KERN_SUCCESS)
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{
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fprintf (stderr, "vm_allocate() failure: %d at %s:%d\n", kt,
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__FILE__, __LINE__);
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break;
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}
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/* Now drop the second half of the allocation to make room for the trampoline table */
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vm_address_t trampoline_page = config_page + PAGE_MAX_SIZE;
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kt = vm_deallocate (mach_task_self (), trampoline_page, PAGE_MAX_SIZE);
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if (kt != KERN_SUCCESS)
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{
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fprintf (stderr, "vm_deallocate() failure: %d at %s:%d\n", kt,
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__FILE__, __LINE__);
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break;
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}
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/* Remap the trampoline table to directly follow the config page */
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vm_prot_t cur_prot;
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vm_prot_t max_prot;
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vm_address_t trampoline_page_template = (vm_address_t)&ffi_closure_trampoline_table_page;
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/* Remap the trampoline table on top of the placeholder page */
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trampoline_page = config_page + PAGE_MAX_SIZE;
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trampoline_page_template = (vm_address_t)&ffi_closure_trampoline_table_page;
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#ifdef __arm__
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/* ffi_closure_trampoline_table_page can be thumb-biased on some ARM archs */
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trampoline_page_template &= ~1UL;
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/* ffi_closure_trampoline_table_page can be thumb-biased on some ARM archs */
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trampoline_page_template &= ~1UL;
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#endif
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kt =
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vm_remap (mach_task_self (), &trampoline_page, PAGE_MAX_SIZE, 0x0, FALSE,
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mach_task_self (), trampoline_page_template, FALSE,
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&cur_prot, &max_prot, VM_INHERIT_SHARE);
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/* If we lost access to the destination trampoline page, drop our config allocation mapping and retry */
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if (kt != KERN_SUCCESS)
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{
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/* Log unexpected failures */
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if (kt != KERN_NO_SPACE)
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{
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fprintf (stderr, "vm_remap() failure: %d at %s:%d\n", kt,
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__FILE__, __LINE__);
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}
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vm_deallocate (mach_task_self (), config_page, PAGE_SIZE);
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continue;
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}
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/* We have valid trampoline and config pages */
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table = calloc (1, sizeof (ffi_trampoline_table));
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table->free_count = FFI_TRAMPOLINE_COUNT;
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table->config_page = config_page;
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table->trampoline_page = trampoline_page;
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/* Create and initialize the free list */
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table->free_list_pool =
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calloc (FFI_TRAMPOLINE_COUNT, sizeof (ffi_trampoline_table_entry));
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uint16_t i;
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for (i = 0; i < table->free_count; i++)
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{
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ffi_trampoline_table_entry *entry = &table->free_list_pool[i];
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entry->trampoline =
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(void *) (table->trampoline_page + (i * FFI_TRAMPOLINE_SIZE));
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if (i < table->free_count - 1)
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entry->next = &table->free_list_pool[i + 1];
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}
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table->free_list = table->free_list_pool;
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kt = vm_remap (mach_task_self (), &trampoline_page, PAGE_MAX_SIZE, 0x0,
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VM_FLAGS_OVERWRITE, mach_task_self (), trampoline_page_template,
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FALSE, &cur_prot, &max_prot, VM_INHERIT_SHARE);
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if (kt != KERN_SUCCESS)
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{
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vm_deallocate (mach_task_self (), config_page, PAGE_MAX_SIZE * 2);
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return NULL;
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}
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/* We have valid trampoline and config pages */
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table = calloc (1, sizeof (ffi_trampoline_table));
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table->free_count = FFI_TRAMPOLINE_COUNT;
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table->config_page = config_page;
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table->trampoline_page = trampoline_page;
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/* Create and initialize the free list */
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table->free_list_pool =
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calloc (FFI_TRAMPOLINE_COUNT, sizeof (ffi_trampoline_table_entry));
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for (i = 0; i < table->free_count; i++)
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{
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ffi_trampoline_table_entry *entry = &table->free_list_pool[i];
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entry->trampoline =
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(void *) (table->trampoline_page + (i * FFI_TRAMPOLINE_SIZE));
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if (i < table->free_count - 1)
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entry->next = &table->free_list_pool[i + 1];
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}
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table->free_list = table->free_list_pool;
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return table;
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}
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static void
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ffi_trampoline_table_free (ffi_trampoline_table *table)
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{
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/* Remove from the list */
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if (table->prev != NULL)
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table->prev->next = table->next;
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if (table->next != NULL)
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table->next->prev = table->prev;
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/* Deallocate pages */
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vm_deallocate (mach_task_self (), table->config_page, PAGE_MAX_SIZE * 2);
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/* Deallocate free list */
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free (table->free_list_pool);
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free (table);
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}
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void *
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ffi_closure_alloc (size_t size, void **code)
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{
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@@ -261,29 +251,7 @@ ffi_closure_free (void *ptr)
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if (table->free_count == FFI_TRAMPOLINE_COUNT
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&& ffi_trampoline_tables != table)
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{
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/* Remove from the list */
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if (table->prev != NULL)
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table->prev->next = table->next;
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if (table->next != NULL)
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table->next->prev = table->prev;
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/* Deallocate pages */
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kern_return_t kt;
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kt = vm_deallocate (mach_task_self (), table->config_page, PAGE_SIZE);
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if (kt != KERN_SUCCESS)
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fprintf (stderr, "vm_deallocate() failure: %d at %s:%d\n", kt,
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__FILE__, __LINE__);
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kt =
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vm_deallocate (mach_task_self (), table->trampoline_page, PAGE_SIZE);
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if (kt != KERN_SUCCESS)
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fprintf (stderr, "vm_deallocate() failure: %d at %s:%d\n", kt,
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__FILE__, __LINE__);
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/* Deallocate free list */
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free (table->free_list_pool);
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free (table);
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ffi_trampoline_table_free (table);
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}
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else if (ffi_trampoline_tables != table)
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{
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