linux-kernel - Re: [PATCH v2 03/13] KVM: selftests: Fudge around an apparent gcc bug in arm64's PMU test

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Message-ID: <ZvseoZLzmaS4MEbc@google.com>
Date: Mon, 30 Sep 2024 14:56:49 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Marc Zyngier <maz@...nel.org>, Oliver Upton <oliver.upton@...ux.dev>, 
	Anup Patel <anup@...infault.org>, Paolo Bonzini <pbonzini@...hat.com>, 
	Christian Borntraeger <borntraeger@...ux.ibm.com>, Janosch Frank <frankja@...ux.ibm.com>, 
	Claudio Imbrenda <imbrenda@...ux.ibm.com>, linux-arm-kernel@...ts.infradead.org, 
	kvmarm@...ts.linux.dev, kvm@...r.kernel.org, kvm-riscv@...ts.infradead.org, 
	linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org, 
	James Houghton <jthoughton@...gle.com>
Subject: Re: [PATCH v2 03/13] KVM: selftests: Fudge around an apparent gcc bug
 in arm64's PMU test

On Wed, Sep 11, 2024, Sean Christopherson wrote:
> Use u64_replace_bits() instead of u64p_replace_bits() to set PMCR.N in
> arm64's vPMU counter access test to fudge around what appears to be a gcc
> bug.  With the recent change to have vcpu_get_reg() return a value in lieu
> of an out-param, some versions of gcc completely ignore the operation
> performed by set_pmcr_n(), i.e. ignore the output param.

Filed a gcc bug: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116912

I'll report back if anything interesting comes out of that bug.