c backend: Implement aligning fields and local/global variables

There are some restrictions here.

- We either need C11 or a compiler that supports the aligned attribute
- We cannot provide align less than the type's natural C alignment.

1 files changed, 18 insertions, 0 deletions

diff --git a/test/behavior/align.zig b/test/behavior/align.zig
index dfa8d895c5..26a914576c 100644
--- a/test/behavior/align.zig
+++ b/test/behavior/align.zig
@@ -163,3 +163,21 @@ test "return error union with 128-bit integer" {
 fn give() anyerror!u128 {
     return 3;
 }
+
+test "page aligned array on stack" {
+    if (builtin.zig_backend == .stage2_x86_64 or builtin.zig_backend == .stage2_arm or
+        builtin.zig_backend == .stage2_wasm) return error.SkipZigTest;
+
+    // Large alignment value to make it hard to accidentally pass.
+    var array align(0x1000) = [_]u8{ 1, 2, 3, 4, 5, 6, 7, 8 };
+    var number1: u8 align(16) = 42;
+    var number2: u8 align(16) = 43;
+
+    try expect(@ptrToInt(&array[0]) & 0xFFF == 0);
+    try expect(array[3] == 4);
+
+    try expect(@truncate(u4, @ptrToInt(&number1)) == 0);
+    try expect(@truncate(u4, @ptrToInt(&number2)) == 0);
+    try expect(number1 == 42);
+    try expect(number2 == 43);
+}