linux-kernel - Re: [linux-next-20250324]/tool/bpf/bpftool fails to complie on linux-next-20250324

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Message-ID: <Z+KXN0KjyHlQPLUj@linux.ibm.com>
Date: Tue, 25 Mar 2025 17:14:55 +0530
From: Saket Kumar Bhaskar <skb99@...ux.ibm.com>
To: Quentin Monnet <qmo@...n.net>
Cc: Venkat Rao Bagalkote <venkat88@...ux.ibm.com>,
        Hari Bathini <hbathini@...ux.ibm.com>, bpf <bpf@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>, linuxppc-dev@...ts.ozlabs.org,
        jkacur@...hat.com, lgoncalv@...hat.com, gmonaco@...hat.com,
        williams@...hat.com, tglozar@...hat.com, rostedt@...dmis.org
Subject: Re: [linux-next-20250324]/tool/bpf/bpftool fails to complie on
 linux-next-20250324

On Tue, Mar 25, 2025 at 11:09:24AM +0000, Quentin Monnet wrote:
> 2025-03-25 16:02 UTC+0530 ~ Venkat Rao Bagalkote <venkat88@...ux.ibm.com>
> > Greetings!!!
> > 
> > 
> > bpftool fails to complie on linux-next-20250324 repo.
> > 
> > 
> > Error:
> > 
> > make: *** No rule to make target 'bpftool', needed by '/home/linux/
> > tools/testing/selftests/bpf/tools/include/vmlinux.h'. Stop.
> > make: *** Waiting for unfinished jobs.....
> 
> 
> Thanks! Would be great to have a bit more context on the error (and on
> how to reproduce) for next time. Bpftool itself seems to compile fine,
> the error shows that it's building it from the context of the selftests
> that seems broken.
> 
> 
Yes, selftest build for BPF fails.
## pwd
/linux/tools/testing/selftests/bpf

# make -j 33

make: *** No rule to make target 'bpftool', needed by '/home/upstreamci/linux/tools/testing/selftests/bpf/tools/include/vmlinux.h'.  Stop.
make: *** Waiting for unfinished jobs....

> > Git bisect points to commit: 8a635c3856ddb74ed3fe7c856b271cdfeb65f293 as
> > first bad commit.
> 
> Thank you Venkat for the bisect!
> 
> On a quick look, that commit introduced a definition for BPFTOOL in
> tools/scripts/Makefile.include:
> 
> 	diff --git a/tools/scripts/Makefile.include .../Makefile.include
> 	index 0aa4005017c7..71bbe52721b3 100644
> 	--- a/tools/scripts/Makefile.include
> 	+++ b/tools/scripts/Makefile.include
> 	@@ -91,6 +91,9 @@ LLVM_CONFIG	?= llvm-config
> 	 LLVM_OBJCOPY	?= llvm-objcopy
> 	 LLVM_STRIP	?= llvm-strip
> 	
> 	+# Some tools require bpftool
> 	+BPFTOOL		?= bpftool
> 	+
> 	 ifeq ($(CC_NO_CLANG), 1)
> 	 EXTRA_WARNINGS += -Wstrict-aliasing=3
> 
> But several utilities or selftests under tools/ include
> tools/scripts/Makefile.include _and_ use their own version of the
> $(BPFTOOL) variable, often assigning only if unset, for example in
> tools/testing/selftests/bpf/Makefile:
> 
> 	BPFTOOL ?= $(DEFAULT_BPFTOOL)
> 
> My guess is that the new definition from Makefile.include overrides this
> with simply "bpftool" as a value, and the Makefile fails to build it as
> a result.
> 
> If I guessed correctly, one workaround would be to rename the variable
> in Makefile.include (and in whatever Makefile now relies on it) into
> something that is not used in the other Makefiles, for example
> BPFTOOL_BINARY.
> 
> Please copy the BPF mailing list on changes impacting BPF tooling (or
> for BPF-related patchsets in general).
> 
> Thanks,
> Quentin
Yes you are right that the new definition from Makefile.include overrides this
with simply "bpftool" as a value, and the Makefile in bpf selftest fails to 
build it as a result.

But the main cause is that it is not able to locate the bpftool binary.
So, is it good idea to both rename this variable in Makefile.include and 
use:

BPFTOOL ?= /usr/sbin/bpftool

This is the link to patch that is impacting: 
https://lore.kernel.org/all/20250218145859.27762-3-tglozar@redhat.com/

Thanks,
Saket