linux-kernel - Re: [PATCH 1/3] tools: testing: Allow importing arch headers in shared.mk

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Message-ID: <DCDAY7MCS3CS.2QJ54F8Z86WN6@google.com>
Date: Wed, 27 Aug 2025 15:07:02 +0000
From: Brendan Jackman <jackmanb@...gle.com>
To: Pedro Falcato <pfalcato@...e.de>
Cc: "Liam R. Howlett" <Liam.Howlett@...cle.com>, Andrew Morton <akpm@...ux-foundation.org>, 
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, Vlastimil Babka <vbabka@...e.cz>, 
	Jann Horn <jannh@...gle.com>, <linux-kernel@...r.kernel.org>, 
	<maple-tree@...ts.infradead.org>, <linux-mm@...ck.org>
Subject: Re: [PATCH 1/3] tools: testing: Allow importing arch headers in shared.mk

On Wed Aug 27, 2025 at 12:50 PM UTC, Pedro Falcato wrote:
> On Wed, Aug 27, 2025 at 11:04:41AM +0000, Brendan Jackman wrote:
>> There is an arch/ tree under tools. This contains some useful stuff, to
>> make that available, import the necessary Make helper file and then add
>> it to the -I flags.
>> 
>> There still aren't that many headers so also just smush all of them into
>> SHARED_DEPS instead of starting to do any header dependency hocus pocus.
>>
>
> I was a little confused as to why this patchset was safe, and - yeah - i missed
> the arch/ under tools/.
>
> There are asm-generic headers so hopefully those fully take care of !x86? 

[Confidently but wihout evidence] yep, without a doubt!

> Did you check?

Um, OK that's fair question. This doesn't support cross-compilation so
you actually need a non-x86 environment.

<begin verbose notes, tl;dr: yeah seems to work for arm64>

I have Nix set up to build aarch64 binaries via binfmt_misc though so I
tried using that...

❯❯  cat /etc/nix/nix.conf
# see https://nixos.org/manual/nix/stable/command-ref/conf-file

sandbox = true

max-jobs = 96

extra-platforms = aarch64-linux

So I dropped this into the root of the kernel repo (and `git add`ed it
otherwise Nix pretends it's not there):

❯❯  cat flake.nix 
{
  inputs = {
    nixpkgs.url = "github:nixos/nixpkgs?ref=nixos-25.05";
  };

  outputs =
    {
      self,
      nixpkgs,
    }:
    let
      system = "aarch64-linux";
      pkgs = import nixpkgs { inherit system; };
    in
    {
      formatter."${system}" = pkgs.nixfmt-tree;

      packages."${system}".vma-tests = pkgs.stdenv.mkDerivation {
        name = "vma-tests";
        src = ./.;
        # (Pretty sure this is not the correct way to do this, there must be
        # some mkDerivation arg that's equivalent to make's -C flag)
        buildPhase = "make -C tools/testing/vma";
        nativeBuildInputs = [ pkgs.liburcu ];

        installPhase = ''
          mkdir $out
          cp tools/testing/vma/vma $out
        '';

	checkPhase = ''./tools/testing/vma'';
      };
    };
}

And, yeah at least it compiles, and that checkPhase should have run the
VMA tests:

❯❯  nix build .#packages.aarch64-linux.vma-tests
warning: Git tree '/usr/local/google/home/jackmanb/src/linux/linux' is dirty

❯❯  file ./result/vma 
./result/vma: ELF 64-bit LSB executable, ARM aarch64, version 1 (SYSV), dynamically linked, interpreter /nix/store/r0pjdp81mmd7dvk5pv1ch75hrbbw60xb-glibc-2.40-66/lib/ld-linux-aarch64.so.1, for GNU/Linux 3.10.0, with debug_info, not stripped

So... that was easier than expected :)