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From: David Gibson <david@gibson.dropbear.id.au>
To: Richard Henderson <richard.henderson@linaro.org>
Cc: Ivan Warren <ivan@vmfacility.fr>,
	qemu-ppc@nongnu.org, qemu-devel@nongnu.org
Subject: Re: [PATCH] target/ppc: Fix truncation of env->hflags
Date: Fri, 29 Jan 2021 11:15:37 +1100	[thread overview]
Message-ID: <20210129001537.GG6951@yekko.fritz.box> (raw)
In-Reply-To: <fed7279c-528c-c4d3-f305-c88ffcdf7bff@linaro.org>

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On Sun, Jan 24, 2021 at 09:38:04AM -1000, Richard Henderson wrote:
> On 1/23/21 6:46 PM, David Gibson wrote:
> > On Sat, Jan 23, 2021 at 05:24:22PM -1000, Richard Henderson wrote:
> >> Use the cs_base field, because it happens to be the same
> >> size as hflags (and MSR, from which hflags is derived).
> >>
> >> In translate, extract most bits from a local hflags variable.
> >> Mark several cases where code generation is *not* derived from
> >> data stored within the hashed elements of the TranslationBlock.
> > 
> > My knowledge of TCG isn't great, so I'm pretty much prepared to accept
> > this is correct on your say so.
> > 
> > But that commit message feels like it's following on from a
> > conversation that's not here, nor linked.  It'd be great if it
> > explained how said hflags truncation is happening, because it's
> > certainly not obvious to someone with only a fair to middling
> > understanding of TCG.
> 
> Mm, fair.
> 
> How about:
> 
> The assignment from env->hflags to tb->flags truncates
> target_ulong to uint32_t.  This loses important bits from
> the top of hflags, which results in incorrect tb selection.
> 
> Use the cs_base field instead, because it happens to be the
> same size as hflags (and MSR fom which hflags is derived).
> 
> In translate, extract most bits from a local hflags variable.
> All of the checks vs env->flags are redundant with env->msr_mask
> in that msr bits cannot be set when the feature is not available.
> Mark several cases where code generation is *not* derived from
> data stored within hashed elements of the tb.

Thanks, I've applied the patch with the updated description.

> 
> 
> r~
> 

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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  parent reply	other threads:[~2021-01-29  0:37 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-24  3:24 [PATCH] target/ppc: Fix truncation of env->hflags Richard Henderson
2021-01-24  4:46 ` David Gibson
2021-01-24 19:38   ` Richard Henderson
2021-01-25 10:03     ` Alex Bennée
2021-01-29  0:15     ` David Gibson [this message]
2021-01-24 12:18 ` Ivan Warren
2021-02-10  4:34 ` David Gibson

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