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

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Message-ID: <20240702003119.3641219-4-briannorris@chromium.org>
Date: Mon,  1 Jul 2024 17:29:17 -0700
From: Brian Norris <briannorris@...omium.org>
To: 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>
Cc: linux-kernel@...r.kernel.org,
	bpf@...r.kernel.org,
	linux-kbuild@...r.kernel.org,
	Masahiro Yamada <masahiroy@...nel.org>,
	Brian Norris <briannorris@...omium.org>
Subject: [PATCH 3/3] tools build: Correct bpf fixdep dependencies

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@...omium.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)
+	$(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