From mboxrd@z Thu Jan  1 00:00:00 1970
From: Mark H Weaver <mhw@netris.org>
Subject: Re: [PATCH 3/6] daemon: On aarch64, use increments of 16 on the stack.
Date: Sat, 05 Aug 2017 17:41:50 -0400
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In-Reply-To: <87r2wp4s6k.fsf@netris.org> (Mark H. Weaver's message of "Sat, 05
	Aug 2017 17:32:03 -0400")
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To: Efraim Flashner <efraim@flashner.co.il>
Cc: guix-devel@gnu.org

I wrote:
> Can you try the following patch on aarch64 and report back?

Actually, the last patch was not quite right.  C/C++ makes it rather
difficult to avoid edge cases in arithmetic.  Can you try this one
instead?

    Thanks,
      Mark

--8<---------------cut here---------------start------------->8---
diff --git a/nix/libstore/build.cc b/nix/libstore/build.cc
index 693fa70c8..63540ddfc 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>
@@ -2008,11 +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;
-#ifdef __aarch64__
-	    pid = clone(childEntry, stack + sizeof(stack) - 16, flags, this);
-#else
-	    pid = clone(childEntry, stack + sizeof(stack) - 8, flags, this);
-#endif
+	/* Ensure proper alignment on the stack.  On aarch64, it has to be 16
+	   bytes.  */
+	pid = clone(childEntry,
+		    (char *)(((uintptr_t)stack + sizeof(stack) - 8) & ~(uintptr_t)0xf),
+		    flags, this);
 	if (pid == -1)
 	    throw SysError("cloning builder process");
     } else
--8<---------------cut here---------------end--------------->8---