Don't use GCC zero-length arrays.

* libguile/frames.c, libguile/objcodes.c, libguile/programs.c,
  libguile/vm-engine.c, libguile/vm-i-system.c, libguile/vm.c: Use
  `SCM_C_OBJCODE_BASE ()' instead of accessing the `base' field of
  `struct scm_objcode'.

* libguile/objcodes.h (struct scm_objcode)[base]: Remove.

libguile/frames.c

@@ -111,7 +111,8 @@ SCM_DEFINE (scm_frame_source, "frame-source", 1, 0, 0,
   bp = SCM_PROGRAM_DATA (SCM_FRAME_PROGRAM (fp));
 
   return scm_c_program_source (SCM_FRAME_PROGRAM (fp),
-                               SCM_VM_FRAME_IP (frame) - bp->base);
+                               SCM_VM_FRAME_IP (frame)
+			       - SCM_C_OBJCODE_BASE (bp));
 }
 #undef FUNC_NAME
 
@@ -219,10 +220,14 @@ SCM_DEFINE (scm_frame_instruction_pointer, "frame-instruction-pointer", 1, 0, 0,
 	    "")
 #define FUNC_NAME s_scm_frame_instruction_pointer
 {
+  const struct scm_objcode *c_objcode;
+
   SCM_VALIDATE_VM_FRAME (1, frame);
+
+  c_objcode = SCM_PROGRAM_DATA (scm_frame_procedure (frame));
   return scm_from_ulong ((unsigned long)
                          (SCM_VM_FRAME_IP (frame)
-                          - SCM_PROGRAM_DATA (scm_frame_procedure (frame))->base));
+                          - SCM_C_OBJCODE_BASE (c_objcode)));
 }
 #undef FUNC_NAME
 

libguile/objcodes.c

@@ -106,17 +106,19 @@ scm_c_make_objcode_slice (SCM parent, const scm_t_uint8 *ptr)
 #define FUNC_NAME "make-objcode-slice"
 {
   const struct scm_objcode *data, *parent_data;
+  const scm_t_uint8 *parent_base;
   SCM ret;
 
   SCM_VALIDATE_OBJCODE (1, parent);
   parent_data = SCM_OBJCODE_DATA (parent);
+  parent_base = SCM_C_OBJCODE_BASE (parent_data);
 
-  if (ptr < parent_data->base
+  if (ptr < parent_base
-      || ptr >= (parent_data->base + parent_data->len + parent_data->metalen
+      || ptr >= (parent_base + parent_data->len + parent_data->metalen
                  - sizeof (struct scm_objcode)))
     scm_misc_error (FUNC_NAME, "offset out of bounds (~a vs ~a + ~a + ~a)",
 		    scm_list_4 (scm_from_ulong ((unsigned long) ptr),
-				scm_from_ulong ((unsigned long)parent_data->base),
+				scm_from_ulong ((unsigned long) parent_base),
 				scm_from_uint32 (parent_data->len),
 				scm_from_uint32 (parent_data->metalen)));
 
@@ -126,8 +128,8 @@ scm_c_make_objcode_slice (SCM parent, const scm_t_uint8 *ptr)
 	   (alignof_type (struct scm_objcode) - 1UL)) == 0);
 
   data = (struct scm_objcode*) ptr;
-  if (data->base + data->len + data->metalen > parent_data->base + parent_data->len + parent_data->metalen)
+  assert (SCM_C_OBJCODE_BASE (data) + data->len + data->metalen
-    abort ();
+	  <= parent_base + parent_data->len + parent_data->metalen);
 
   SCM_NEWSMOB2 (ret, scm_tc16_objcode, data, parent);
   SCM_SET_SMOB_FLAGS (ret, SCM_F_OBJCODE_IS_SLICE);

libguile/objcodes.h

@@ -21,14 +21,20 @@
 
 #include <libguile.h>
 
-/* objcode data should be directly mappable to this C structure. */
+/* Objcode data should be directly mappable to this C structure.  */
-struct scm_objcode {
+struct scm_objcode
+{
   scm_t_uint32 len;             /* the maximum index of base[] */
   scm_t_uint32 metalen;         /* well, i lie. this many bytes at the end of
                                    base[] for metadata */
-  scm_t_uint8 base[0];
+  /* In C99, we'd have:
+     scm_t_uint8 base[];  */
 };
 
+/* Return a pointer to the base of objcode OBJ.  */
+#define SCM_C_OBJCODE_BASE(obj)				\
+  ((scm_t_uint8 *)(obj) + sizeof (struct scm_objcode))
+
 #define SCM_F_OBJCODE_IS_MMAP     (1<<0)
 #define SCM_F_OBJCODE_IS_U8VECTOR (1<<1)
 #define SCM_F_OBJCODE_IS_SLICE    (1<<2)
@@ -42,7 +48,7 @@ SCM_API scm_t_bits scm_tc16_objcode;
 #define SCM_OBJCODE_LEN(x)	(SCM_OBJCODE_DATA (x)->len)
 #define SCM_OBJCODE_META_LEN(x)	(SCM_OBJCODE_DATA (x)->metalen)
 #define SCM_OBJCODE_TOTAL_LEN(x) (SCM_OBJCODE_LEN (x) + SCM_OBJCODE_META_LEN (x))
-#define SCM_OBJCODE_BASE(x)	(SCM_OBJCODE_DATA (x)->base)
+#define SCM_OBJCODE_BASE(x)	(SCM_C_OBJCODE_BASE (SCM_OBJCODE_DATA (x)))
 
 #define SCM_OBJCODE_IS_MMAP(x)	(SCM_SMOB_FLAGS (x) & SCM_F_OBJCODE_IS_MMAP)
 #define SCM_OBJCODE_IS_U8VECTOR(x) (SCM_SMOB_FLAGS (x) & SCM_F_OBJCODE_IS_U8VECTOR)

libguile/programs.c

@@ -96,9 +96,12 @@ SCM_DEFINE (scm_program_base, "program-base", 1, 0, 0,
 	    "")
 #define FUNC_NAME s_scm_program_base
 {
+  const struct scm_objcode *c_objcode;
+
   SCM_VALIDATE_PROGRAM (1, program);
 
-  return scm_from_ulong ((unsigned long) SCM_PROGRAM_DATA (program)->base);
+  c_objcode = SCM_PROGRAM_DATA (program);
+  return scm_from_ulong ((unsigned long) SCM_C_OBJCODE_BASE (c_objcode));
 }
 #undef FUNC_NAME
 

libguile/vm-engine.c

@@ -92,7 +92,7 @@ VM_NAME (struct scm_vm *vp, SCM program, SCM *argv, int nargs)
     CACHE_PROGRAM ();
     PUSH (program);
     fp = sp + 1;
-    ip = bp->base;
+    ip = SCM_C_OBJCODE_BASE (bp);
     /* MV-call frame, function & arguments */
     PUSH ((SCM)fp); /* dynamic link */
     PUSH (0); /* mvra */

libguile/vm-i-system.c

@@ -764,7 +764,7 @@ VM_DEFINE_INSTRUCTION (54, call, "call", 1, -1, 1)
       ASSERT (SCM_FRAME_MV_RETURN_ADDRESS (fp) == 0);
       SCM_FRAME_SET_RETURN_ADDRESS (fp, ip);
       SCM_FRAME_SET_MV_RETURN_ADDRESS (fp, 0);
-      ip = bp->base;
+      ip = SCM_C_OBJCODE_BASE (bp);
       ENTER_HOOK ();
       APPLY_HOOK ();
       NEXT;
@@ -841,7 +841,7 @@ VM_DEFINE_INSTRUCTION (55, goto_args, "goto/args", 1, -1, 1)
 
       NULLSTACK (old_sp - sp);
 
-      ip = bp->base;
+      ip = SCM_C_OBJCODE_BASE (bp);
 
       ENTER_HOOK ();
       APPLY_HOOK ();
@@ -929,7 +929,7 @@ VM_DEFINE_INSTRUCTION (58, mv_call, "mv-call", 4, -1, 1)
       ASSERT (SCM_FRAME_MV_RETURN_ADDRESS (fp) == 0);
       SCM_FRAME_SET_RETURN_ADDRESS (fp, ip);
       SCM_FRAME_SET_MV_RETURN_ADDRESS (fp, mvra);
-      ip = bp->base;
+      ip = SCM_C_OBJCODE_BASE (bp);
       ENTER_HOOK ();
       APPLY_HOOK ();
       NEXT;

libguile/vm.c

@@ -190,7 +190,7 @@ really_make_boot_program (long nargs)
   text[1] = (scm_t_uint8)nargs;
 
   bp = scm_malloc (sizeof (struct scm_objcode) + sizeof (text));
-  memcpy (bp->base, text, sizeof (text));
+  memcpy (SCM_C_OBJCODE_BASE (bp), text, sizeof (text));
   bp->len = sizeof(text);
   bp->metalen = 0;