Re: [PATCH v2 3/3] tools build: Correct bpf fixdep dependencies

[Jiri Olsa <olsajiri@gmail.com>]

On Tue, Jul 02, 2024 at 02:58:39PM -0700, Brian Norris 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@chromium.org>

lgtm

Acked-by: Jiri Olsa <jolsa@kernel.org>

thanks,
jirka

> ---
> 
> 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/Makefile       | 14 ++++++++++++--
>  2 files changed, 23 insertions(+), 3 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/Makefile b/tools/lib/bpf/Makefile
> index 2cf892774346..630369c0091e 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 +143,13 @@ all: fixdep
>  
>  all_cmd: $(CMD_TARGETS) check
>  
> -$(BPF_IN_SHARED): force $(BPF_GENERATED)
> +$(SHARED_OBJDIR):
> +	$(Q)mkdir -p $@
> +
> +$(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 +159,11 @@ $(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
> -- 
> 2.45.2.803.g4e1b14247a-goog
> 
>