protobuf-c: remove tmp_alloc and max_alloca fields of ProtobufCAllocator

i'm confused as to why these fields exist, since the typical
implementation of a "temporary alloc" would be something like alloca(),
and alloca() is usually just inlined code that adjusts the stack
pointer, which is not a function whose address could be taken.

this breaks the API/ABI and will require a note in the ChangeLog.

possibly we could revisit the idea of "temporary allocations" by using
C99 variable length arrays. this would have the advantage of being
standardized, unlike alloca().

protobuf-c/protobuf-c.c

@@ -72,11 +72,6 @@
  */
 #define MAX_MEMBERS_FOR_HASH_SIZE	128
 
-/* Convenience macros. */
-
-#define TMPALLOC(allocator, size) \
-	((allocator)->tmp_alloc((allocator)->allocator_data, (size)))
-
 /* Try to allocate memory, running some special code if it fails. */
 #define DO_ALLOC(dst, allocator, size, fail_code)			\
 do {									\
@@ -173,8 +168,6 @@ system_free(void *allocator_data, void *data)
 ProtobufCAllocator protobuf_c_default_allocator = {
 	.alloc = system_alloc,
 	.free = system_free,
-	.tmp_alloc = NULL,
-	.max_alloca = 8192,
 	.allocator_data = NULL,
 };
 
@@ -2337,6 +2330,7 @@ protobuf_c_message_unpack(const ProtobufCMessageDescriptor *desc,
 	unsigned in_slab_index = 0; /* number of members in the slab */
 	size_t n_unknown = 0;
 	unsigned f;
+	unsigned j;
 	unsigned i_slab;
 	unsigned last_field_index = 0;
 	unsigned char required_fields_bitmap[MAX_MEMBERS_FOR_HASH_SIZE / 8] =
@@ -2471,15 +2465,10 @@ protobuf_c_message_unpack(const ProtobufCMessageDescriptor *desc,
 			which_slab++;
 			size = sizeof(ScannedMember)
 				<< (which_slab + FIRST_SCANNED_MEMBER_SLAB_SIZE_LOG2);
-			if (allocator->tmp_alloc != NULL) {
-				scanned_member_slabs[which_slab] =
-					TMPALLOC(allocator, size);
-			} else {
 			DO_ALLOC(scanned_member_slabs[which_slab],
 				 allocator, size,
 				 goto error_cleanup_during_scan);
 		}
-		}
 		scanned_member_slabs[which_slab][in_slab_index++] = tmp;
 
 		if (field != NULL && field->label == PROTOBUF_C_LABEL_REPEATED) {
@@ -2574,30 +2563,21 @@ protobuf_c_message_unpack(const ProtobufCMessageDescriptor *desc,
 	}
 
 	/* cleanup */
-	if (allocator->tmp_alloc == NULL) {
-		unsigned j;
 	for (j = 1; j <= which_slab; j++)
 		FREE(allocator, scanned_member_slabs[j]);
-	}
 
 	return rv;
 
 error_cleanup:
 	protobuf_c_message_free_unpacked(rv, allocator);
-	if (allocator->tmp_alloc == NULL) {
-		unsigned j;
 	for (j = 1; j <= which_slab; j++)
 		FREE(allocator, scanned_member_slabs[j]);
-	}
 	return NULL;
 
 error_cleanup_during_scan:
 	FREE(allocator, rv);
-	if (allocator->tmp_alloc == NULL) {
-		unsigned j;
 	for (j = 1; j <= which_slab; j++)
 		FREE(allocator, scanned_member_slabs[j]);
-	}
 	return NULL;
 }
 

protobuf-c/protobuf-c.h

@@ -145,8 +145,6 @@ struct _ProtobufCAllocator
 {
 	void		*(*alloc)(void *allocator_data, size_t size);
 	void		(*free)(void *allocator_data, void *pointer);
-	void		*(*tmp_alloc)(void *allocator_data, size_t size);
-	unsigned	max_alloca;
 	void		*allocator_data;
 };
 

t/generated-code2/test-generated-code2.c

@@ -1520,7 +1520,9 @@ static void test_free (void *allocator_data, void *data)
 }
 
 static ProtobufCAllocator test_allocator = {
-  test_alloc, test_free, 0, 0, &test_allocator_data
+  .alloc = test_alloc,
+  .free = test_free,
+  .allocator_data = &test_allocator_data,
 };
 
 #define SETUP_TEST_ALLOC_BUFFER(pbuf, len)					\