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

[ludo@gnu.org (Ludovic Courtès)]

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Efraim Flashner <efraim@flashner.co.il> 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’.


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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