From 58ee5f4e61cd9b7a9ba65798e2214efa3753a733 Mon Sep 17 00:00:00 2001
From: LemonBoy <thatlemon@gmail.com>
Date: Sun, 20 Sep 2020 00:10:53 +0200
Subject: [PATCH] std: Fix metadata corruption in HeapAllocator

HeapAllocator stores the pointer returned by HeapAlloc right after the
data block and, after the recent allocator refactoring, the space for
this pointer was not taken into account in the calculation of the final
block size.

Fixes #5830
---
 lib/std/heap.zig | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/std/heap.zig b/lib/std/heap.zig
index 6db1be539c..16de215cc2 100644
--- a/lib/std/heap.zig
+++ b/lib/std/heap.zig
@@ -489,7 +489,7 @@ pub const HeapAllocator = switch (builtin.os.tag) {
                 const full_len = os.windows.kernel32.HeapSize(heap_handle, 0, ptr);
                 assert(full_len != std.math.maxInt(usize));
                 assert(full_len >= amt);
-                break :init mem.alignBackwardAnyAlign(full_len - (aligned_addr - root_addr), len_align);
+                break :init mem.alignBackwardAnyAlign(full_len - (aligned_addr - root_addr) - @sizeOf(usize), len_align);
             };
             const buf = @intToPtr([*]u8, aligned_addr)[0..return_len];
             getRecordPtr(buf).* = root_addr;