01/01: daemon: Ensure proper alignment on the stack.

[Efraim Flashner]

efraim pushed a commit to branch master
in repository guix.

commit ab4ccc8fcfaf2215d4b33b1376147e4c2c70426a
Author: Efraim Flashner <address@hidden>
Date:   Tue Feb 14 21:48:30 2017 +0200

    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 cebc404..9b7bb53 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