Merge branch 'feature/c-layout' into develop

CHANGELOG.md

@@ -2,6 +2,9 @@
 All notable changes to this project will be documented in this file. This change log follows the conventions of [keepachangelog.com](http://keepachangelog.com/).
 
 ## [Unreleased]
+### Added
+- New `coffi.layout` namespace with support for forcing C layout rules on structs
+
 ### Fixed
 - C-characters were being read as UTF-16 rather than ASCII code points
 

src/clj/coffi/layout.clj

@@ -0,0 +1,30 @@
+(ns coffi.layout
+  "Functions for adjusting the layout of structs."
+  (:require
+   [coffi.mem :as mem]))
+
+(defn with-c-layout
+  "Forces a struct specification to C layout rules.
+
+  This will add padding fields between fields to match C alignment
+  requirements."
+  [struct-spec]
+  (let [aligned-fields
+        (loop [offset 0
+               aligned-fields []
+               fields (nth struct-spec 1)]
+          (if (seq fields)
+            (let [[[_ type :as field] & fields] fields
+                  size (mem/size-of type)
+                  r (rem offset (mem/align-of type))]
+              (recur (cond-> (+ offset size)
+                       (pos? r) (+ (- size r)))
+                     (cond-> aligned-fields
+                       (pos? r) (conj [::padding [::mem/padding (- size r)]])
+                       :always (conj field))
+                     fields))
+            (let [strongest-alignment (mem/align-of struct-spec)
+                  r (rem offset strongest-alignment)]
+              (cond-> aligned-fields
+                (pos? r) (conj [::padding [::mem/padding (- strongest-alignment r)]])))))]
+    (assoc struct-spec 1 aligned-fields)))

src/clj/coffi/mem.clj

@@ -349,6 +349,11 @@
   [type]
   (.byteSize ^MemoryLayout (c-layout type)))
 
+(defn align-of
+  "The alignment in bytes of the given `type`."
+  [type]
+  (.byteAlignment ^MemoryLayout (c-layout type)))
+
 (defn alloc-instance
   "Allocates a memory segment for the given `type`."
   ([type] (alloc-instance type (connected-scope)))
@@ -776,7 +781,8 @@
   aliased type."
   {:style/indent [:defn]}
   [new-type aliased-type]
-  (if (primitive-type aliased-type)
+  (if (and (s/valid? ::type aliased-type)
+           (primitive-type aliased-type))
     `(let [aliased# ~aliased-type]
        (defmethod primitive-type ~new-type
          [_type#]
@@ -799,4 +805,4 @@
          (deserialize-from segment# aliased#)))))
 (s/fdef defalias
   :args (s/cat :new-type qualified-keyword?
-               :aliased-type ::type))
+               :aliased-type any?))

test/c/ffi_test.c

@@ -48,3 +48,18 @@ StringFactory get_downcall(int whichString) {
         return 0;
     }
 }
+
+typedef struct alignment_test {
+    char a;
+    double x;
+    float y;
+} AlignmentTest;
+
+AlignmentTest get_struct() {
+    AlignmentTest ret = {};
+    ret.a = 'x';
+    ret.x = 3.14;
+    ret.y = 42.0;
+
+    return ret;
+}

test/clj/coffi/ffi_test.clj

@@ -1,8 +1,9 @@
 (ns coffi.ffi-test
   (:require
    [clojure.test :as t]
-   [coffi.mem :as mem]
-   [coffi.ffi :as ffi]))
+   [coffi.ffi :as ffi]
+   [coffi.layout :as layout]
+   [coffi.mem :as mem]))
 
 (ffi/load-library "target/ffi_test.so")
 
@@ -30,3 +31,16 @@
   (t/is (= ((ffi/cfn "upcall_test" [[::ffi/fn [] ::mem/c-string]] ::mem/c-string)
             (fn [] "hello"))
            "hello")))
+
+(mem/defalias ::alignment-test
+  (layout/with-c-layout
+    [::mem/struct
+     [[:a ::mem/char]
+      [:x ::mem/double]
+      [:y ::mem/float]]]))
+
+(t/deftest padding-matches
+  (t/is (= (dissoc ((ffi/cfn "get_struct" [] ::alignment-test)) ::layout/padding)
+           {:a \x
+            :x 3.14
+            :y 42.0})))