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From: Quentin Monnet <quentin@isovalent.com>
To: Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Andrii Nakryiko <andrii@kernel.org>
Cc: netdev@vger.kernel.org, bpf@vger.kernel.org,
	Quentin Monnet <quentin@isovalent.com>
Subject: [PATCH bpf-next 3/3] bpftool: turn check on zlib from a phony target into a conditional error
Date: Sat,  9 Oct 2021 22:03:41 +0100	[thread overview]
Message-ID: <20211009210341.6291-4-quentin@isovalent.com> (raw)
In-Reply-To: <20211009210341.6291-1-quentin@isovalent.com>

One of bpftool's object files depends on zlib. To make sure we do not
attempt to build that object when the library is not available, commit
d66fa3c70e59 ("tools: bpftool: add feature check for zlib") introduced a
feature check to detect whether zlib is present.

This check comes as a rule for which the target ("zdep") is a
nonexistent file (phony target), which means that the Makefile always
attempts to rebuild it. It is mostly harmless. However, one side effect
is that, on running again once bpftool is already built, make considers
that "something" (the recipe for zdep) was executed, and does not print
the usual message "make: Nothing to be done for 'all'", which is a
user-friendly indicator that the build went fine.

Before, with some level of debugging information:

    $ make --debug=m
    [...]
    Reading makefiles...

    Auto-detecting system features:
    ...                        libbfd: [ on  ]
    ...        disassembler-four-args: [ on  ]
    ...                          zlib: [ on  ]
    ...                        libcap: [ on  ]
    ...               clang-bpf-co-re: [ on  ]

    Updating makefiles....
    Updating goal targets....
     File 'all' does not exist.
           File 'zdep' does not exist.
          Must remake target 'zdep'.
     File 'all' does not exist.
    Must remake target 'all'.
    Successfully remade target file 'all'.

After the patch:

    $ make --debug=m
    [...]

    Auto-detecting system features:
    ...                        libbfd: [ on  ]
    ...        disassembler-four-args: [ on  ]
    ...                          zlib: [ on  ]
    ...                        libcap: [ on  ]
    ...               clang-bpf-co-re: [ on  ]

    Updating makefiles....
    Updating goal targets....
     File 'all' does not exist.
    Must remake target 'all'.
    Successfully remade target file 'all'.
    make: Nothing to be done for 'all'.

(Note the last line, which is not part of make's debug information.)

Signed-off-by: Quentin Monnet <quentin@isovalent.com>
---
 tools/bpf/bpftool/Makefile | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/tools/bpf/bpftool/Makefile b/tools/bpf/bpftool/Makefile
index 4acec74f459b..2174e21aa57b 100644
--- a/tools/bpf/bpftool/Makefile
+++ b/tools/bpf/bpftool/Makefile
@@ -199,7 +199,10 @@ $(BOOTSTRAP_OUTPUT)disasm.o: $(srctree)/kernel/bpf/disasm.c
 $(OUTPUT)disasm.o: $(srctree)/kernel/bpf/disasm.c
 	$(QUIET_CC)$(CC) $(CFLAGS) -c -MMD -o $@ $<
 
-$(OUTPUT)feature.o: | zdep
+$(OUTPUT)feature.o:
+ifneq ($(feature-zlib), 1)
+	$(error "No zlib found")
+endif
 
 $(BPFTOOL_BOOTSTRAP): $(BOOTSTRAP_OBJS) $(LIBBPF_BOOTSTRAP)
 	$(QUIET_LINK)$(HOSTCC) $(CFLAGS) $(LDFLAGS) -o $@ $(BOOTSTRAP_OBJS) \
@@ -255,10 +258,7 @@ doc-uninstall:
 
 FORCE:
 
-zdep:
-	@if [ "$(feature-zlib)" != "1" ]; then echo "No zlib found"; exit 1 ; fi
-
 .SECONDARY:
-.PHONY: all FORCE clean install-bin install uninstall zdep
+.PHONY: all FORCE clean install-bin install uninstall
 .PHONY: doc doc-clean doc-install doc-uninstall
 .DEFAULT_GOAL := all
-- 
2.30.2


  parent reply	other threads:[~2021-10-09 21:03 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-10-09 21:03 [PATCH bpf-next 0/3] fixes for bpftool's Makefile Quentin Monnet
2021-10-09 21:03 ` [PATCH bpf-next 1/3] bpftool: fix install for libbpf's internal header(s) Quentin Monnet
2021-10-19 23:44   ` Andrii Nakryiko
2021-10-09 21:03 ` [PATCH bpf-next 2/3] bpftool: do not FORCE-build libbpf Quentin Monnet
2021-10-09 21:03 ` Quentin Monnet [this message]
2021-10-18 14:05 ` [PATCH bpf-next 0/3] fixes for bpftool's Makefile John Fastabend
2021-10-19 23:44   ` Andrii Nakryiko

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