linux-kernel - Re: [PATCH 00/23] kbuild: support building external modules in a separate build directory

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Message-ID: <CANiq72mWvnnJqFKU_YYUmtbG0oQAB7AyEMRCk7w0mC6T9kEoGg@mail.gmail.com>
Date: Mon, 30 Sep 2024 16:28:58 +0200
From: Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
To: Masahiro Yamada <masahiroy@...nel.org>
Cc: linux-kbuild@...r.kernel.org, Miguel Ojeda <ojeda@...nel.org>, 
	rust-for-linux <rust-for-linux@...r.kernel.org>, linux-kernel@...r.kernel.org, 
	Nathan Chancellor <nathan@...nel.org>, Nicolas Schier <nicolas@...sle.eu>
Subject: Re: [PATCH 00/23] kbuild: support building external modules in a
 separate build directory

On Sat, Sep 28, 2024 at 8:50 AM Masahiro Yamada <masahiroy@...nel.org> wrote:
>
> I CC'ed rust ML because Ack for the following patches are appreciated.
>
> [07/23] kbuild: remove unnecessary prune of rust/alloc for rustfmt
> [08/23] kbuild: simplify find command for rustfmt
> [11/23] kbuild: check the presence of include/generated/rustc_cfg

Sorry, it was in my backlog after the conferences.

I am not sure what the base of the series was, but ran my usual tests
on top of v6.11 and then on top of `rust-fixes` after some manual
adjustment in both cases, and things appear to still work fine (i.e.
what I usually build, without taking advantage of the separate build
directory support).

Moreover, I tested the separate build directory support (`MO=`), for a
trivial Rust out-of-tree module, with a subdir as well as with a
directory outside the out-of-tree source code.

I also tested the new approach suggested for the out-of-tree
`Makefile` (i.e. `export KBUILD_EXTMOD` and `include
$(KDIR)/Makefile`), and it all worked as expected, so:

Tested-by: Miguel Ojeda <ojeda@...nel.org>

...except for arm64, where I found that I needed this bit:

diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile
index b058c4803efb..4cd9a1f2ec3d 100644
--- a/arch/arm64/Makefile
+++ b/arch/arm64/Makefile
@@ -71,7 +71,7 @@ stack_protector_prepare: prepare0
                                -mstack-protector-guard-reg=sp_el0        \
                                -mstack-protector-guard-offset=$(shell    \
                        awk '{if ($$2 == "TSK_STACK_CANARY") print $$3;}' \
-                                       include/generated/asm-offsets.h))
+
$(objtree)/include/generated/asm-offsets.h))
 endif

 ifeq ($(CONFIG_ARM64_BTI_KERNEL),y)

Cheers,
Miguel