linux-kernel - RE: [PATCH] KVM: selftests: add -MP to CFLAGS

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Message-ID: <3fa5bdded7504d6582cf01f4db4cd6b4@AcuMS.aculab.com>
Date:   Sun, 29 Oct 2023 21:13:41 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'David Woodhouse' <dwmw2@...radead.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>
CC:     Paolo Bonzini <pbonzini@...hat.com>, Shuah Khan <shuah@...nel.org>,
        "linux-kselftest@...r.kernel.org" <linux-kselftest@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] KVM: selftests: add -MP to CFLAGS

From: David Woodhouse
> Sent: 28 October 2023 20:35
> 
> Using -MD without -MP causes build failures when a header file is deleted
> or moved. With -MP, the compiler will emit phony targets for the header
> files it lists as dependencies, and the Makefiles won't refuse to attempt
> to rebuild a C unit which no longer includes the deleted header.

Won't a phony target stop a header being built if there is
an actual rule to build it?

I usually add:

%.h:
	echo "Ignoring stale dependency for $@"

Which only applies if there isn't an explicit rule.

	David

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