Re: [PATCH] target/ppc: Fix truncation of env->hflags

[David Gibson <david@gibson.dropbear.id.au>]

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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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