From 947c87b558f860a3d87fe1aed6cc96f94fc00cb2 Mon Sep 17 00:00:00 2001
From: Andrew Kelley <andrew@ziglang.org>
Date: Thu, 4 Apr 2019 01:34:13 -0400
Subject: threads: fix using unmapped memory in some cases

as pointed out in #musl IRC, the memory for the fs register address
value needs to be taken into account in the mmap call.
---
 std/os.zig | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

(limited to 'std/os.zig')

diff --git a/std/os.zig b/std/os.zig
index 1416f3d49e..b89b2a9ce2 100644
--- a/std/os.zig
+++ b/std/os.zig
@@ -3142,6 +3142,8 @@ pub fn spawnThread(context: var, comptime startFn: var) SpawnThreadError!*Thread
                 l = mem.alignForward(l, tls_phdr.p_align);
                 tls_start_offset = l;
                 l += tls_phdr.p_memsz;
+                // the fs register address
+                l += @sizeOf(usize);
             }
         }
         break :blk l;
@@ -3184,7 +3186,7 @@ pub fn spawnThread(context: var, comptime startFn: var) SpawnThreadError!*Thread
         var newtls: usize = undefined;
         if (linux_tls_phdr) |tls_phdr| {
             @memcpy(@intToPtr([*]u8, mmap_addr + tls_start_offset), linux_tls_img_src, tls_phdr.p_filesz);
-            newtls = mmap_addr + mmap_len;
+            newtls = mmap_addr + mmap_len - @sizeOf(usize);
             @intToPtr(*usize, newtls).* = newtls;
             flags |= posix.CLONE_SETTLS;
         }
-- 
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