From ab4ccc8fcfaf2215d4b33b1376147e4c2c70426a Mon Sep 17 00:00:00 2001
From: Efraim Flashner <efraim@flashner.co.il>
Date: Tue, 14 Feb 2017 21:48:30 +0200
Subject: daemon: Ensure proper alignment on the stack.

* nix/libstore/build.cc (startBuilder): When calling 'clone', increase
the step to 16 and ensure it aligns properly on the stack.
---
 nix/libstore/build.cc | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/nix/libstore/build.cc b/nix/libstore/build.cc
index cebc404d1c..9b7bb5391c 100644
--- a/nix/libstore/build.cc
+++ b/nix/libstore/build.cc
@@ -26,6 +26,7 @@
 #include <errno.h>
 #include <stdio.h>
 #include <cstring>
+#include <stdint.h>
 
 #include <pwd.h>
 #include <grp.h>
@@ -2008,7 +2009,11 @@ void DerivationGoal::startBuilder()
 	char stack[32 * 1024];
 	int flags = CLONE_NEWPID | CLONE_NEWNS | CLONE_NEWIPC | CLONE_NEWUTS | SIGCHLD;
 	if (!fixedOutput) flags |= CLONE_NEWNET;
-	pid = clone(childEntry, stack + sizeof(stack) - 8, flags, this);
+
+	/* Ensure proper alignment on the stack.  On aarch64, it has to be 16
+	   bytes.  */
+	pid = clone(childEntry, (char *)(((uintptr_t)stack + 16) & ~0xf),
+		    flags, this);
 	if (pid == -1)
 	    throw SysError("cloning builder process");
     } else
-- 
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