Subject: [PATCH] Support calling foreign functions of 10 or more arguments

From: Mark H Weaver <[email-masked]>
Date: Tue, 26 Feb 2013 17:40:09 -0500

Hi Andy,

Andy Wingo <[email-masked]> writes:

> On Mon 25 Feb 2013 01:34, Mark H Weaver <[email-masked]> writes:
>
>> The current limitation of 10 arguments to foreign functions is proving
>> to be a problem for some libraries, in particular the Allegro game
>> library.
>>
>> Is there a reason why raising this limit to 16 or 20 would be
>> undesirable?  What tradeoffs are involved?
>
> Each arity of foreign functions gets a little VM program stub that
> checks the argument count then actually does the call.  We statically
> generate the first N of those arities (currently 10), and then for the
> rest we should dynamically allocate the objcode stubs.  Dynamic
> allocation is currently unimplemented.

I've attached a patch that implements dynamic allocation of objcode
stubs for larger arities.  What do you think?

   Thanks,
     Mark

>From 29aaa7add08849503bde5a9be43b162e492a4297 Mon Sep 17 00:00:00 2001
From: Mark H Weaver <[email-masked]>
Date: Tue, 26 Feb 2013 17:25:51 -0500
Subject: [PATCH] Support calling foreign functions of 10 or more arguments.

* libguile/foreign.c (large_objcode_trampolines,
  large_objcode_trampolines_mutex): New static variables.
  (make_objcode_trampoline, get_objcode_trampoline): New static
  functions.
  (cif_to_procedure): Use 'get_objcode_trampoline'.
  (scm_init_foreign): Initialize 'large_objcode_trampolines'.

* test-suite/standalone/test-ffi-lib.c (test_ffi_sum_many):
  New function.

* test-suite/standalone/test-ffi: Add test.
---
 libguile/foreign.c                   |   59 ++++++++++++++++++++++++++++++----
 test-suite/standalone/test-ffi       |   15 +++++++++
 test-suite/standalone/test-ffi-lib.c |   17 ++++++++++
 3 files changed, 84 insertions(+), 7 deletions(-)

diff --git a/libguile/foreign.c b/libguile/foreign.c
index f5819c4..f8b88de 100644
--- a/libguile/foreign.c
+++ b/libguile/foreign.c
@@ -880,21 +880,64 @@ static const SCM objcode_trampolines[10] = {
   SCM_PACK (objcode_cells.cells+18),
 };
 
+static SCM large_objcode_trampolines;
+static scm_i_pthread_mutex_t large_objcode_trampolines_mutex =
+  SCM_I_PTHREAD_MUTEX_INITIALIZER;
+
 static SCM
-cif_to_procedure (SCM cif, SCM func_ptr)
+make_objcode_trampoline (unsigned int nargs)
 {
-  ffi_cif *c_cif;
-  unsigned int nargs;
-  SCM objcode, table, ret;
+  const int size = sizeof (struct scm_objcode) + 8
+    + sizeof (struct scm_objcode) + 32;
+  const scm_t_uint8 *bytes_0 = raw_bytecode.bytes + 0;
+  const scm_t_uint8 *bytes_1 = raw_bytecode.bytes + size;
+  SCM bytecode = scm_c_make_bytevector (size);
+  scm_t_uint8 *bytes = (scm_t_uint8 *) SCM_BYTEVECTOR_CONTENTS (bytecode);
+  int i;
+
+  for (i = 0; i < size; i++)
+    {
+      if (bytes_0[i] == bytes_1[i])
+        bytes[i] = bytes_0[i];
+      else if (bytes_0[i] == 0 && bytes_1[i] == 1)
+        bytes[i] = nargs;
+      else
+        scm_syserror ("make_objcode_trampoline");
+    }
+  return scm_bytecode_to_native_objcode (bytecode);
+}
 
-  c_cif = (ffi_cif *) SCM_POINTER_VALUE (cif);
-  nargs = c_cif->nargs;
+static SCM
+get_objcode_trampoline (unsigned int nargs)
+{
+  SCM objcode;
 
   if (nargs < 10)
     objcode = objcode_trampolines[nargs];
+  else if (nargs < 256)
+    {
+      scm_i_scm_pthread_mutex_lock (&large_objcode_trampolines_mutex);
+      objcode = scm_c_vector_ref (large_objcode_trampolines, nargs);
+      if (SCM_UNBNDP (objcode))
+        scm_c_vector_set_x (large_objcode_trampolines, nargs,
+                            objcode = make_objcode_trampoline (nargs));
+      scm_i_pthread_mutex_unlock (&large_objcode_trampolines_mutex);
+    }
   else
-    scm_misc_error ("make-foreign-function", "args >= 10 currently unimplemented",
+    scm_misc_error ("make-foreign-function", "args >= 256 currently unimplemented",
                     SCM_EOL);
+
+  return objcode;
+}
+
+static SCM
+cif_to_procedure (SCM cif, SCM func_ptr)
+{
+  ffi_cif *c_cif;
+  SCM objcode, table, ret;
+
+  c_cif = (ffi_cif *) SCM_POINTER_VALUE (cif);
+  objcode = get_objcode_trampoline (c_cif->nargs);
   
   table = scm_c_make_vector (2, SCM_UNDEFINED);
   SCM_SIMPLE_VECTOR_SET (table, 0, scm_cons (cif, func_ptr));
@@ -1308,6 +1351,8 @@ scm_init_foreign (void)
 
   null_pointer = scm_cell (scm_tc7_pointer, 0);
   scm_define (sym_null, null_pointer);
+
+  large_objcode_trampolines = scm_c_make_vector (256, SCM_UNDEFINED);
 }
 
 void
diff --git a/test-suite/standalone/test-ffi b/test-suite/standalone/test-ffi
index ad68660..0a91f63 100755
--- a/test-suite/standalone/test-ffi
+++ b/test-suite/standalone/test-ffi
@@ -170,6 +170,21 @@ exec guile -q -s "$0" "$@"
       (+ -1 2000 -30000 40000000000))
 
 ;;
+;; More than ten arguments
+;;
+(define f-sum-many
+  (pointer->procedure int64 (dynamic-func "test_ffi_sum_many" lib)
+                      (list uint8 uint16 uint32 uint64
+                            int8 int16 int32 int64
+                            int8 int16 int32 int64)))
+(test (f-sum-many 255 65535 4294967295 1844674407370955161
+                  -1 2000 -30000 40000000000
+                  5 -6000 70000 -80000000000)
+      (+ 255 65535 4294967295 1844674407370955161
+                  -1 2000 -30000 40000000000
+                  5 -6000 70000 -80000000000))
+
+;;
 ;; Structs
 ;;
 (define f-sum-struct
diff --git a/test-suite/standalone/test-ffi-lib.c b/test-suite/standalone/test-ffi-lib.c
index 37d6e43..f265339 100644
--- a/test-suite/standalone/test-ffi-lib.c
+++ b/test-suite/standalone/test-ffi-lib.c
@@ -194,6 +194,23 @@ scm_t_int64 test_ffi_sum (scm_t_int8 a, scm_t_int16 b,
 }

+scm_t_int64 test_ffi_sum_many (scm_t_uint8 a, scm_t_uint16 b,
+                               scm_t_uint32 c, scm_t_uint64 d,
+                               scm_t_int8 e, scm_t_int16 f,
+                               scm_t_int32 g, scm_t_int64 h,
+                               scm_t_int8 i, scm_t_int16 j,
+                               scm_t_int32 k, scm_t_int64 l);
+scm_t_int64 test_ffi_sum_many (scm_t_uint8 a, scm_t_uint16 b,
+                               scm_t_uint32 c, scm_t_uint64 d,
+                               scm_t_int8 e, scm_t_int16 f,
+                               scm_t_int32 g, scm_t_int64 h,
+                               scm_t_int8 i, scm_t_int16 j,
+                               scm_t_int32 k, scm_t_int64 l)
+{
+  return l + k + j + i + h + g + f + e + d + c + b + a;
+}
+
+
 struct foo
 {
   scm_t_int8 a;
-- 
1.7.10.4