linux-kernel - Re: [PATCH v3] bpf: Remove custom build rule

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Message-ID: <235234d8-a223-4170-876a-6ccbf552c09c@oracle.com>
Date: Thu, 29 Aug 2024 11:12:46 +0100
From: Alan Maguire <alan.maguire@...cle.com>
To: Alexey Gladkov <legion@...nel.org>, linux-kernel@...r.kernel.org,
        bpf@...r.kernel.org, linux-kbuild@...r.kernel.org
Cc: Masahiro Yamada <masahiroy@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Andrii Nakryiko <andrii@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Oleg Nesterov <oleg@...hat.com>
Subject: Re: [PATCH v3] bpf: Remove custom build rule

On 28/08/2024 19:10, Alexey Gladkov wrote:
> According to the documentation, when building a kernel with the C=2
> parameter, all source files should be checked. But this does not happen
> for the kernel/bpf/ directory.
> 
> $ touch kernel/bpf/core.c
> $ make C=2 CHECK=true kernel/bpf/core.o
> 
> Outputs:
> 
>   CHECK   scripts/mod/empty.c
>   CALL    scripts/checksyscalls.sh
>   DESCEND objtool
>   INSTALL libsubcmd_headers
>   CC      kernel/bpf/core.o
> 
> As can be seen the compilation is done, but CHECK is not executed. This
> happens because kernel/bpf/Makefile has defined its own rule for
> compilation and forgotten the macro that does the check.
> 
> There is no need to duplicate the build code, and this rule can be
> removed to use generic rules.
> 
> Signed-off-by: Alexey Gladkov <legion@...nel.org>

Tested-by: Alan Maguire <alan.maguire@...cle.com>

The aim from the BPF side is just to share the btf_iter.c,
btf_relocate.c and relo_core.c files for both libbpf and kernel build.
Those files need to live in tools/lib/bpf because the libbpf standalone
repo on github is built from tools/lib/bpf.

Since the approach in this patch continues to support that while it
doesn't break other things like check targets it's definitely preferred.

Thanks for the fix!

Alan

> ---
>  kernel/bpf/Makefile       | 6 ------
>  kernel/bpf/btf_iter.c     | 2 ++
>  kernel/bpf/btf_relocate.c | 2 ++
>  kernel/bpf/relo_core.c    | 2 ++
>  4 files changed, 6 insertions(+), 6 deletions(-)
>  create mode 100644 kernel/bpf/btf_iter.c
>  create mode 100644 kernel/bpf/btf_relocate.c
>  create mode 100644 kernel/bpf/relo_core.c
> 
> diff --git a/kernel/bpf/Makefile b/kernel/bpf/Makefile
> index 0291eef9ce92..9b9c151b5c82 100644
> --- a/kernel/bpf/Makefile
> +++ b/kernel/bpf/Makefile
> @@ -52,9 +52,3 @@ obj-$(CONFIG_BPF_PRELOAD) += preload/
>  obj-$(CONFIG_BPF_SYSCALL) += relo_core.o
>  obj-$(CONFIG_BPF_SYSCALL) += btf_iter.o
>  obj-$(CONFIG_BPF_SYSCALL) += btf_relocate.o
> -
> -# Some source files are common to libbpf.
> -vpath %.c $(srctree)/kernel/bpf:$(srctree)/tools/lib/bpf
> -
> -$(obj)/%.o: %.c FORCE
> -	$(call if_changed_rule,cc_o_c)
> diff --git a/kernel/bpf/btf_iter.c b/kernel/bpf/btf_iter.c
> new file mode 100644
> index 000000000000..eab8493a1669
> --- /dev/null
> +++ b/kernel/bpf/btf_iter.c
> @@ -0,0 +1,2 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +#include "../../tools/lib/bpf/btf_iter.c"
> diff --git a/kernel/bpf/btf_relocate.c b/kernel/bpf/btf_relocate.c
> new file mode 100644
> index 000000000000..8c89c7b59ef8
> --- /dev/null
> +++ b/kernel/bpf/btf_relocate.c
> @@ -0,0 +1,2 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +#include "../../tools/lib/bpf/btf_relocate.c"
> diff --git a/kernel/bpf/relo_core.c b/kernel/bpf/relo_core.c
> new file mode 100644
> index 000000000000..6a36fbc0e5ab
> --- /dev/null
> +++ b/kernel/bpf/relo_core.c
> @@ -0,0 +1,2 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +#include "../../tools/lib/bpf/relo_core.c"