linux-kernel - Re: [PATCH v4 3/3] tools build: Correct bpf fixdep dependencies

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Message-ID: <CAEf4BzaY=6dVShaXmnjKPLB6xRdMbM0Gtz08A=rwgq2SR66L9Q@mail.gmail.com>
Date: Fri, 19 Jul 2024 11:31:25 -0700
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Brian Norris <briannorris@...omium.org>
Cc: Arnaldo Carvalho de Melo <acme@...hat.com>, Namhyung Kim <namhyung@...nel.org>, 
	Ian Rogers <irogers@...gle.com>, Thomas Richter <tmricht@...ux.ibm.com>, 
	Josh Poimboeuf <jpoimboe@...nel.org>, Peter Zijlstra <peterz@...radead.org>, linux-kernel@...r.kernel.org, 
	Masahiro Yamada <masahiroy@...nel.org>, bpf@...r.kernel.org, linux-kbuild@...r.kernel.org, 
	Jiri Olsa <jolsa@...nel.org>
Subject: Re: [PATCH v4 3/3] tools build: Correct bpf fixdep dependencies

On Mon, Jul 15, 2024 at 1:37 PM Brian Norris <briannorris@...omium.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])
>
> I also need to tweak the assignment of the OUTPUT variable, so that
> relative path builds work. For example, for 'make tools/lib/bpf', OUTPUT
> is unset, and is usually treated as "cwd" -- but recursive make will
> change cwd and so OUTPUT has a new meaning. For consistency, I ensure
> OUTPUT is always an absolute path.
>
> And $(Q) gets a backup definition in tools/build/Makefile.include,
> because Makefile.include is sometimes included without
> tools/build/Makefile, so the "quiet command" stuff doesn't actually work
> consistently without it.
>
> 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@...omium.org>
> Acked-by: Jiri Olsa <jolsa@...nel.org>
> ---
>

LGTM

Acked-by: Andrii Nakryiko <andrii@...nel.org>

> Changes in v4:
>  - update tools/lib/bpf/.gitignore to exclude 'fixdep'
>  - update tools/lib/bpf `make clean` target for fixdep
>  - combine $(SHARED_OBJDIR) and $(STATIC_OBJDIR) rules
>
> Changes in v3:
>  - add Jiri's Acked-by
>
> Changes in v2:
>  - also fix libbpf shared library rules
>  - ensure OUTPUT is always set, and always an absolute path
>  - add backup $(Q) definition in tools/build/Makefile.include
>
>  tools/build/Makefile.include | 12 +++++++++++-
>  tools/lib/bpf/.gitignore     |  1 +
>  tools/lib/bpf/Makefile       | 13 ++++++++++---
>  3 files changed, 22 insertions(+), 4 deletions(-)
>
> diff --git a/tools/build/Makefile.include b/tools/build/Makefile.include
> index 8dadaa0fbb43..0e4de83400ac 100644
> --- a/tools/build/Makefile.include
> +++ b/tools/build/Makefile.include
> @@ -1,8 +1,18 @@
>  # 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)
> +  Q ?=
> +  SILENT_MAKE = +$(Q)$(MAKE)
> +else
> +  Q ?= @
> +  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/.gitignore b/tools/lib/bpf/.gitignore
> index 0da84cb9e66d..f02725b123b3 100644
> --- a/tools/lib/bpf/.gitignore
> +++ b/tools/lib/bpf/.gitignore
> @@ -5,3 +5,4 @@ TAGS
>  tags
>  cscope.*
>  /bpf_helper_defs.h
> +fixdep
> diff --git a/tools/lib/bpf/Makefile b/tools/lib/bpf/Makefile
> index 2cf892774346..1b22f0f37288 100644
> --- a/tools/lib/bpf/Makefile
> +++ b/tools/lib/bpf/Makefile
> @@ -108,6 +108,8 @@ MAKEOVERRIDES=
>
>  all:
>
> +OUTPUT ?= ./
> +OUTPUT := $(abspath $(OUTPUT))/
>  export srctree OUTPUT CC LD CFLAGS V
>  include $(srctree)/tools/build/Makefile.include
>
> @@ -141,7 +143,10 @@ all: fixdep
>
>  all_cmd: $(CMD_TARGETS) check
>
> -$(BPF_IN_SHARED): force $(BPF_GENERATED)
> +$(SHARED_OBJDIR) $(STATIC_OBJDIR):
> +       $(Q)mkdir -p $@
> +
> +$(BPF_IN_SHARED): force $(BPF_GENERATED) | $(SHARED_OBJDIR)
>         @(test -f ../../include/uapi/linux/bpf.h -a -f ../../../include/uapi/linux/bpf.h && ( \
>         (diff -B ../../include/uapi/linux/bpf.h ../../../include/uapi/linux/bpf.h >/dev/null) || \
>         echo "Warning: Kernel ABI header at 'tools/include/uapi/linux/bpf.h' differs from latest version at 'include/uapi/linux/bpf.h'" >&2 )) || true
> @@ -151,9 +156,11 @@ $(BPF_IN_SHARED): force $(BPF_GENERATED)
>         @(test -f ../../include/uapi/linux/if_xdp.h -a -f ../../../include/uapi/linux/if_xdp.h && ( \
>         (diff -B ../../include/uapi/linux/if_xdp.h ../../../include/uapi/linux/if_xdp.h >/dev/null) || \
>         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
> +       $(SILENT_MAKE) -C $(srctree)/tools/build CFLAGS= LDFLAGS= OUTPUT=$(SHARED_OBJDIR) $(SHARED_OBJDIR)fixdep
>         $(Q)$(MAKE) $(build)=libbpf OUTPUT=$(SHARED_OBJDIR) CFLAGS="$(CFLAGS) $(SHLIB_FLAGS)"
>
> -$(BPF_IN_STATIC): force $(BPF_GENERATED)
> +$(BPF_IN_STATIC): force $(BPF_GENERATED) | $(STATIC_OBJDIR)
> +       $(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
> @@ -263,7 +270,7 @@ install_pkgconfig: $(PC_FILE)
>
>  install: install_lib install_pkgconfig install_headers
>
> -clean:
> +clean: fixdep-clean
>         $(call QUIET_CLEAN, libbpf) $(RM) -rf $(CMD_TARGETS)                 \
>                 *~ .*.d .*.cmd LIBBPF-CFLAGS $(BPF_GENERATED)                \
>                 $(SHARED_OBJDIR) $(STATIC_OBJDIR)                            \
> --
> 2.45.2.993.g49e7a77208-goog
>
>