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/* -----------------------------------------------------------------------------
* libffi-based adjustor thunk logic.
* ---------------------------------------------------------------------------*/
#include "rts/PosixSource.h"
#include "Rts.h"
#include "RtsUtils.h"
#include "StablePtr.h"
#include "sm/Storage.h"
#include "Hash.h"
#include "ffi.h"
#include <string.h>
/* Maps AdjustorExecutable* to AdjustorWritable*. */
static HashTable* allocatedExecs;
static AdjustorWritable allocate_adjustor(AdjustorExecutable *exec_ret)
{
AdjustorWritable writ;
ffi_closure* cl;
ACQUIRE_SM_LOCK;
cl = writ = ffi_closure_alloc(sizeof(ffi_closure), exec_ret);
if (cl != NULL) {
if (allocatedExecs == NULL) {
allocatedExecs = allocHashTable();
}
insertHashTable(allocatedExecs, (StgWord)*exec_ret, writ);
}
RELEASE_SM_LOCK;
return writ;
}
static AdjustorWritable exec_to_writable(AdjustorExecutable exec)
{
AdjustorWritable writ;
ACQUIRE_SM_LOCK;
if (allocatedExecs == NULL ||
(writ = lookupHashTable(allocatedExecs, (StgWord)exec)) == NULL) {
RELEASE_SM_LOCK;
barf("exec_to_writable: not found");
}
RELEASE_SM_LOCK;
return writ;
}
static void free_adjustor(AdjustorExecutable exec)
{
AdjustorWritable writ;
ffi_closure* cl;
cl = writ = exec_to_writable(exec);
ACQUIRE_SM_LOCK;
removeHashTable(allocatedExecs, (StgWord)exec, writ);
ffi_closure_free(cl);
RELEASE_SM_LOCK;
}
/* Note [Freeing libffi adjustors]
* ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
*
* HOW ADJUSTORS/CLOSURES WORK ON LIBFFI:
* libffi's ffi_closure_alloc() function gives you two pointers to a closure,
* 1. the writable pointer, and 2. the executable pointer. You write the
* closure into the writable pointer (and ffi_prep_closure_loc() will do this
* for you) and you execute it at the executable pointer.
*
* THE PROBLEM:
* The RTS deals only with the executable pointer, but when it comes time to
* free the closure, libffi wants the writable pointer back that it gave you
* when you allocated it.
*
* On Linux we used to solve this problem by storing the address of the writable
* mapping into itself, then returning both writable and executable pointers
* plus 1 machine word for preparing the closure for use by the RTS (see the
* Linux version of allocateExec() in rts/sm/Storage.c). When we want to recover
* the writable address, we subtract 1 word from the executable address and
* fetch. This works because Linux kernel magic gives us two pointers with
* different addresses that refer to the same memory. Whatever you write into
* the writable address can be read back at the executable address. This method
* is very efficient.
*
* On iOS this breaks for two reasons: 1. the two pointers do not refer to
* the same memory (so we can't retrieve anything stored into the writable
* pointer if we only have the exec pointer), and 2. libffi's
* ffi_closure_alloc() assumes the pointer it has returned you is a
* ffi_closure structure and treats it as such: It uses that memory to
* communicate with ffi_prep_closure_loc(). On Linux by contrast
* ffi_closure_alloc() is viewed simply as a memory allocation, and only
* ffi_prep_closure_loc() deals in ffi_closure structures. Each of these
* differences is enough make the efficient way used on Linux not work on iOS.
* Instead on iOS we use hash tables to recover the writable address from the
* executable one. This method is conservative and would almost certainly work
* on any platform. This is what we now do everywhere.
*/
void
freeHaskellFunctionPtr(void* ptr)
{
ffi_closure *cl;
cl = exec_to_writable(ptr);
freeStablePtr(cl->user_data);
stgFree(cl->cif->arg_types);
stgFree(cl->cif);
free_adjustor(ptr);
}
static ffi_type * char_to_ffi_type(char c)
{
switch (c) {
case 'v': return &ffi_type_void;
case 'f': return &ffi_type_float;
case 'd': return &ffi_type_double;
case 'L': return &ffi_type_sint64;
case 'l': return &ffi_type_uint64;
case 'W': return &ffi_type_sint32;
case 'w': return &ffi_type_uint32;
case 'S': return &ffi_type_sint16;
case 's': return &ffi_type_uint16;
case 'B': return &ffi_type_sint8;
case 'b': return &ffi_type_uint8;
case 'p': return &ffi_type_pointer;
default: barf("char_to_ffi_type: unknown type '%c'", c);
}
}
void*
createAdjustor (int cconv,
StgStablePtr hptr,
StgFunPtr wptr,
char *typeString)
{
ffi_cif *cif;
ffi_type **arg_types;
uint32_t n_args, i;
ffi_type *result_type;
ffi_closure *cl;
int r, abi;
void *code;
n_args = strlen(typeString) - 1;
cif = stgMallocBytes(sizeof(ffi_cif), "createAdjustor");
arg_types = stgMallocBytes(n_args * sizeof(ffi_type*), "createAdjustor");
result_type = char_to_ffi_type(typeString[0]);
for (i=0; i < n_args; i++) {
arg_types[i] = char_to_ffi_type(typeString[i+1]);
}
switch (cconv) {
#if defined(mingw32_HOST_OS) && defined(i386_HOST_ARCH)
case 0: /* stdcall */
abi = FFI_STDCALL;
break;
#endif /* defined(mingw32_HOST_OS) && defined(i386_HOST_ARCH) */
case 1: /* ccall */
abi = FFI_DEFAULT_ABI;
break;
default:
barf("createAdjustor: convention %d not supported on this platform", cconv);
}
r = ffi_prep_cif(cif, abi, n_args, result_type, arg_types);
if (r != FFI_OK) barf("ffi_prep_cif failed: %d", r);
cl = allocate_adjustor(&code);
if (cl == NULL) {
barf("createAdjustor: failed to allocate memory");
}
r = ffi_prep_closure_loc(cl, cif, (void*)wptr, hptr/*userdata*/, code);
if (r != FFI_OK) barf("ffi_prep_closure_loc failed: %d", r);
return (void*)code;
}
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