From 0d0103458989598a4de011bdbc7c61c27d7b053b Mon Sep 17 00:00:00 2001
From: Rui Ueyama <ruiu@cs.stanford.edu>
Date: Sun, 6 Sep 2020 21:06:15 +0900
Subject: [PATCH] Support global struct bitfield initializer

---
 parse.c         | 32 +++++++++++++++++++++++++++++---
 test/bitfield.c | 14 ++++++++++++++
 2 files changed, 43 insertions(+), 3 deletions(-)

diff --git a/parse.c b/parse.c
index 4421f96..9ee1520 100644
--- a/parse.c
+++ b/parse.c
@@ -1074,6 +1074,18 @@ static Node *lvar_initializer(Token **rest, Token *tok, Var *var) {
   return new_binary(ND_COMMA, lhs, rhs, tok);
 }
 
+static uint64_t read_buf(char *buf, int sz) {
+  if (sz == 1)
+    return *buf;
+  if (sz == 2)
+    return *(uint16_t *)buf;
+  if (sz == 4)
+    return *(uint32_t *)buf;
+  if (sz == 8)
+    return *(uint64_t *)buf;
+  unreachable();
+}
+
 static void write_buf(char *buf, uint64_t val, int sz) {
   if (sz == 1)
     *buf = val;
@@ -1097,9 +1109,23 @@ write_gvar_data(Relocation *cur, Initializer *init, Type *ty, char *buf, int off
   }
 
   if (ty->kind == TY_STRUCT) {
-    for (Member *mem = ty->members; mem; mem = mem->next)
-      cur = write_gvar_data(cur, init->children[mem->idx], mem->ty, buf,
-                            offset + mem->offset);
+    for (Member *mem = ty->members; mem; mem = mem->next) {
+      if (mem->is_bitfield) {
+        Node *expr = init->children[mem->idx]->expr;
+        if (!expr)
+          break;
+
+        char *loc = buf + offset + mem->offset;
+        uint64_t oldval = read_buf(loc, mem->ty->size);
+        uint64_t newval = eval(expr);
+        uint64_t mask = (1L << mem->bit_width) - 1;
+        uint64_t combined = oldval | ((newval & mask) << mem->bit_offset);
+        write_buf(loc, combined, mem->ty->size);
+      } else {
+        cur = write_gvar_data(cur, init->children[mem->idx], mem->ty, buf,
+                              offset + mem->offset);
+      }
+    }
     return cur;
   }
 
diff --git a/test/bitfield.c b/test/bitfield.c
index 9a63acc..501a03f 100644
--- a/test/bitfield.c
+++ b/test/bitfield.c
@@ -1,5 +1,11 @@
 #include "test.h"
 
+struct {
+  char a;
+  int b : 5;
+  int c : 10;
+} g45 = {1, 2, 3}, g46={};
+
 int main() {
   ASSERT(4, sizeof(struct {int x:1; }));
   ASSERT(8, sizeof(struct {long x:1; }));
@@ -20,6 +26,14 @@ int main() {
   ASSERT(-4, ({ struct bit1 x={1,2,3,4,5}; x.d; }));
   ASSERT(-3, ({ struct bit1 x={1,2,3,4,5}; x.e; }));
 
+  ASSERT(1, g45.a);
+  ASSERT(2, g45.b);
+  ASSERT(3, g45.c);
+
+  ASSERT(0, g46.a);
+  ASSERT(0, g46.b);
+  ASSERT(0, g46.c);
+
   printf("OK\n");
   return 0;
 }
-- 
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