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Re: [PATCH 2/3] x86/shadow: Don't use signed bitfield in sh_emulate_ctxt


  • To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
  • From: Bertrand Marquis <Bertrand.Marquis@xxxxxxx>
  • Date: Mon, 9 May 2022 12:40:36 +0000
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  • Cc: Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Jan Beulich <JBeulich@xxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>
  • Delivery-date: Mon, 09 May 2022 12:41:06 +0000
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  • Thread-topic: [PATCH 2/3] x86/shadow: Don't use signed bitfield in sh_emulate_ctxt

Hi Andrew,

> On 9 May 2022, at 13:24, Andrew Cooper <andrew.cooper3@xxxxxxxxxx> wrote:
> 
> 'int' bitfields in particular have implementation defined behaviour under gcc
> and can change signed-ness with -funsigned-bitfields.
> 
> There is no need for low_bit_was_clear to be a bitfield in the first place; it
> is only used as a boolean.  Doing so even improves the code generation in
> sh_emulate_map_dest() to avoid emitting a merge with structure padding.
> 
> Spotted by Eclair MISRA scanner.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Reviewed-by: Bertrand Marquis <bertrand.marquis@xxxxxxx>

Is in fact only used as boolean in hvm.c so does make sense.

Cheers
Bertrand




 


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