Re: [PATCH 3/6] daemon: On aarch64, use increments of 16 on the stack.

[Ludovic Courtès]

Efraim Flashner <address@hidden> skribis:

> man2 clone: EINVAL: ... on aarch64, child_stack must be a multiple of 16.
>
> * nix/libstore/build.cc (DerivationGoal::startBuilder): When on aarch64,
> when calling clone(), increment the stack by 16.
> ---
>  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 cebc404d1..362b2d91d 100644
> --- a/nix/libstore/build.cc
> +++ b/nix/libstore/build.cc
> @@ -2008,7 +2008,12 @@ 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);
> +// if statements are hard, fix this
> +//#if __AARCH64__
> +     pid = clone(childEntry, stack + sizeof(stack) - 16, flags, this);
> +//#else
> +//   pid = clone(childEntry, stack + sizeof(stack) - 8, flags, this);
> +//#endif

I think we can make it unconditional.  Could you test whether the
attached patch works for aarch64?

Thanks!

Ludo’.

diff --git a/nix/libstore/build.cc b/nix/libstore/build.cc
index cebc404d1..9b7bb5391 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