01/01: daemon: Ensure the child stack is aligned on a 16-byte boundary.

[Mark H. Weaver]

mhw pushed a commit to branch master
in repository guix.

commit a1aa5dabaa5d570710da7190a3c3dca5442b9daa
Author: Mark H Weaver <address@hidden>
Date:   Mon Aug 7 16:41:03 2017 -0400

    daemon: Ensure the child stack is aligned on a 16-byte boundary.
    
    * nix/libstore/build.cc (DerivationGoal::startBuilder): When calling 
'clone',
    ensure that the stack is aligned on a 16-byte boundary.
---
 nix/libstore/build.cc | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/nix/libstore/build.cc b/nix/libstore/build.cc
index 693fa70..63540dd 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