linux-kernel - Re: [RFC PATCH v3 08/31] KVM: selftests: Require GCC to realign stacks on function entry

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Message-ID: <Y+1ajq5PiGgq1q9Q@google.com>
Date:   Wed, 15 Feb 2023 14:19:58 -0800
From:   Sean Christopherson <seanjc@...gle.com>
To:     "Maciej S. Szmigiero" <mail@...iej.szmigiero.name>
Cc:     Ackerley Tng <ackerleytng@...gle.com>, erdemaktas@...gle.com,
        linux-kselftest@...r.kernel.org, pbonzini@...hat.com,
        isaku.yamahata@...el.com, sagis@...gle.com, afranji@...gle.com,
        runanwang@...gle.com, shuah@...nel.org, drjones@...hat.com,
        maz@...nel.org, bgardon@...gle.com, jmattson@...gle.com,
        dmatlack@...gle.com, peterx@...hat.com, oupton@...gle.com,
        ricarkol@...gle.com, yang.zhong@...el.com, wei.w.wang@...el.com,
        xiaoyao.li@...el.com, pgonda@...gle.com, marcorr@...gle.com,
        eesposit@...hat.com, borntraeger@...ibm.com, eric.auger@...hat.com,
        wangyanan55@...wei.com, aaronlewis@...gle.com, vkuznets@...hat.com,
        pshier@...gle.com, axelrasmussen@...gle.com,
        zhenzhong.duan@...el.com, like.xu@...ux.intel.com,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [RFC PATCH v3 08/31] KVM: selftests: Require GCC to realign
 stacks on function entry

On Wed, Feb 15, 2023, Maciej S. Szmigiero wrote:
> On 15.02.2023 01:50, Ackerley Tng wrote:
> > To fix this, I propose that in vm_arch_vcpu_add(), we align the
> > allocated stack address and then subtract 8 from that:
> 
> Note that if this code is ever used to launch a vCPU with 32-bit entry
> point it will need to subtract 4 bytes instead of 8 bytes.
> 
> I think it would be worthwhile to at least place a comment mentioning
> this near the stack aligning expression so nobody misses this fact.

Heh, I've no objection to a comment, though this really is the tip of the iceberg
if we want to add 32-bit guest support in selftests.