Hi Masahiro,
On Sun, Aug 28, 2022 at 11:39:53AM +0900, Masahiro Yamada wrote:
> Kbuild builds init/built-in.a twice; first during the ordinary
> directory descending, second from scripts/link-vmlinux.sh.
>
> We do this because UTS_VERSION contains the build version and the
> timestamp. We cannot update it during the normal directory traversal
> since we do not yet know if we need to update vmlinux. UTS_VERSION is
> temporarily calculated, but omitted from the update check. Otherwise,
> vmlinux would be rebuilt every time.
>
> When Kbuild results in running link-vmlinux.sh, it increments the
> version number in the .version file and takes the timestamp at that
> time to really fix UTS_VERSION.
>
> However, updating the same file twice is a footgun. To avoid nasty
> timestamp issues, all build artifacts that depend on init/built-in.a
> must be atomically generated in link-vmlinux.sh, where some of them
> do not need rebuilding.
>
> To fix this issue, this commit changes as follows:
>
> [1] Split UTS_VERSION out to include/generated/utsversion.h from
> include/generated/compile.h
>
> include/generated/utsversion.h is generated just before the
> vmlinux link. It is generated under include/generated/ because
> some decompressors (s390, x86) use UTS_VERSION.
>
> [2] Split init_uts_ns and linux_banner out to init/version-timestamp.c
> from init/version.c
>
> init_uts_ns and linux_banner contain UTS_VERSION. During the ordinary
> directory descending, they are compiled with __weak and used to
> determine if vmlinux needs relinking. Just before the vmlinux link,
> they are compiled without __weak to embed the real version and
> timestamp.
>
> Signed-off-by: Masahiro Yamada <masahiroy@xxxxxxxxxx>
<snip>
> diff --git a/init/build-version b/init/build-version
> new file mode 100755
> index 000000000000..39225104f14d
> --- /dev/null
> +++ b/init/build-version
> @@ -0,0 +1,10 @@
> +#!/bin/sh
> +# SPDX-License-Identifier: GPL-2.0-only
> +
> +VERSION=$(cat .version) 2>/dev/null &&
> +VERSION=$(expr $VERSION + 1) 2>/dev/null ||
> +VERSION=1
> +
> +echo ${VERSION} > .version
> +
> +echo ${VERSION}
I am seeing
cat: .version: No such file or directory
at some point in nearly all of my builds in -next. Does the 2>/dev/null
want to be moved into the subshell?
Cheers,
Nathan
