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Implement FFI_EXEC_TRAMPOLINE_TABLE allocator for iOS/ARM.

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This provides working closure support on iOS/ARM devices where
PROT_WRITE|PROT_EXEC is not permitted. The code passes basic
smoke tests, but requires further review.
This commit is contained in:
Landon Fuller
2010-09-19 14:36:45 -07:00
parent b00ff3e98f
commit 83038cf24a
3 changed files with 219 additions and 83 deletions
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80
src/closures.c
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@@ -65,85 +65,7 @@
# if FFI_EXEC_TRAMPOLINE_TABLE
// XXX - non-thread-safe, non-portable implementation, intended for initial testing
#include <mach/mach.h>
#include <stdio.h>
#include <stdlib.h>
extern void *ffi_closure_trampoline_table;
static void *tramp_table = NULL;
static void **config_table = NULL;
static int tramp_table_free = 0;
void *
ffi_closure_alloc (size_t size, void **code)
{
if (!code)
return NULL;
/* Allocate our config page and remap the trampoline table */
while (tramp_table == NULL) {
vm_address_t config_page = 0x0;
kern_return_t kt;
/* Try to allocate two pages */
kt = vm_allocate(mach_task_self(), &config_page, PAGE_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 */
kt = vm_deallocate(mach_task_self(), config_page+PAGE_SIZE, PAGE_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_address_t table_page = config_page+PAGE_SIZE;
vm_prot_t cur_prot;
vm_prot_t max_prot;
kt = vm_remap(mach_task_self(), &table_page, PAGE_SIZE, 0x0, FALSE, mach_task_self(), (vm_address_t) &ffi_closure_trampoline_table, 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;
}
tramp_table = (void *) table_page;
config_table = (void **) config_page;
config_table += 4; // XXX - there's a 16 byte offset into the config page on ARM
fprintf(stderr, "[DEBUG] Allocated config page at %p, trampoline page at %p, configs start at %p\n", (void *) config_page, (void *) table_page, config_table);
}
/* Check for permanent allocation failure */
if (tramp_table == NULL)
return *code = NULL;
*code = tramp_table + (3 * tramp_table_free);
tramp_table_free++;
void *closure = malloc(size);
return closure;
}
void
ffi_closure_free (void *ptr)
{
// TODO
//free (ptr);
}
// Per-target implementation; It's unclear what can reasonable be shared between two OS/architecture implementations.
# elif FFI_MMAP_EXEC_WRIT /* !FFI_EXEC_TRAMPOLINE_TABLE */