Re: [PATCH 3/3] tools build: Correct bpf fixdep dependencies

Andrii Nakryiko
2024-07-02T00:50:48Z

On Mon, Jul 1, 2024 at 5:32 PM Brian Norris <briannorris@chromium.org> wrote:
>
> The dependencies in tools/lib/bpf/Makefile are incorrect. Before we
> recurse to build $(BPF_IN_STATIC), we need to build its 'fixdep'
> executable.
>
> I can't use the usual shortcut from Makefile.include:
>
> <target>: <sources> fixdep
>
> because its 'fixdep' target relies on $(OUTPUT), and $(OUTPUT) differs
> in the parent 'make' versus the child 'make' -- so I imitate it via
> open-coding.
>
> I tweak a few $(MAKE) invocations while I'm at it, because
> 1. I'm adding a new recursive make; and
> 2. these recursive 'make's print spurious lines about files that are "up
> to date" (which isn't normally a feature in Kbuild subtargets) or
> "jobserver not available" (see [1])
>
> After this change, top-level builds result in an empty grep result from:
>
> $ grep 'cannot find fixdep' $(find tools/ -name '*.cmd')
>
> [1] https://www.gnu.org/software/make/manual/html_node/MAKE-Variable.html
> If we're not using $(MAKE) directly, then we need to use more '+'.
>
> Signed-off-by: Brian Norris <briannorris@chromium.org>
> ---
>
> tools/build/Makefile.include | 10 +++++++++-
> tools/lib/bpf/Makefile | 6 +++++-
> 2 files changed, 14 insertions(+), 2 deletions(-)
>
> diff --git a/tools/build/Makefile.include b/tools/build/Makefile.include
> index 8dadaa0fbb43..c95e4773b826 100644
> --- a/tools/build/Makefile.include
> +++ b/tools/build/Makefile.include
> @@ -1,8 +1,16 @@
> # SPDX-License-Identifier: GPL-2.0-only
> build := -f $(srctree)/tools/build/Makefile.build dir=. obj
>
> +# More than just $(Q), we sometimes want to suppress all command output from a
> +# recursive make -- even the 'up to date' printout.
> +ifeq ($(V),1)
> + SILENT_MAKE = +$(Q)$(MAKE)
> +else
> + SILENT_MAKE = +$(Q)$(MAKE) --silent
> +endif
> +
> fixdep:
> - $(Q)$(MAKE) -C $(srctree)/tools/build CFLAGS= LDFLAGS= $(OUTPUT)fixdep
> + $(SILENT_MAKE) -C $(srctree)/tools/build CFLAGS= LDFLAGS= $(OUTPUT)fixdep
>
> fixdep-clean:
> $(Q)$(MAKE) -C $(srctree)/tools/build clean
> diff --git a/tools/lib/bpf/Makefile b/tools/lib/bpf/Makefile
> index 2cf892774346..0743cf653615 100644
> --- a/tools/lib/bpf/Makefile
> +++ b/tools/lib/bpf/Makefile
> @@ -153,7 +153,11 @@ $(BPF_IN_SHARED): force $(BPF_GENERATED)
> echo "Warning: Kernel ABI header at 'tools/include/uapi/linux/if_xdp.h' differs from latest version at 'include/uapi/linux/if_xdp.h'" >&2 )) || true
> $(Q)$(MAKE) $(build)=libbpf OUTPUT=$(SHARED_OBJDIR) CFLAGS="$(CFLAGS) $(SHLIB_FLAGS)"
>
> -$(BPF_IN_STATIC): force $(BPF_GENERATED)
> +$(STATIC_OBJDIR):
> + $(Q)mkdir -p $@
> +
> +$(BPF_IN_STATIC): force $(BPF_GENERATED) | $(STATIC_OBJDIR)

wouldn't $(BPF_IN_SHARED) target need a similar treatment?

> + $(SILENT_MAKE) -C $(srctree)/tools/build CFLAGS= LDFLAGS= OUTPUT=$(STATIC_OBJDIR) $(STATIC_OBJDIR)fixdep
> $(Q)$(MAKE) $(build)=libbpf OUTPUT=$(STATIC_OBJDIR)
>
> $(BPF_HELPER_DEFS): $(srctree)/tools/include/uapi/linux/bpf.h
> --
> 2.45.2.803.g4e1b14247a-goog
>
>