From: Wei Liu <wei.liu2@citrix.com>
To: Andrew Cooper <andrew.cooper3@citrix.com>
Cc: "Roger Pau Monné" <roger.pau@citrix.com>,
"Wei Liu" <wei.liu2@citrix.com>,
"Jan Beulich" <JBeulich@suse.com>,
Xen-devel <xen-devel@lists.xen.org>
Subject: Re: [PATCH v2 1/5] x86/entry: Correct comparisons against boolean variables
Date: Fri, 2 Mar 2018 17:32:03 +0000 [thread overview]
Message-ID: <20180302173203.jdkxsaho2xbi5lsd@citrix.com> (raw)
In-Reply-To: <1519743036-11600-2-git-send-email-andrew.cooper3@citrix.com>
On Tue, Feb 27, 2018 at 02:50:32PM +0000, Andrew Cooper wrote:
> The correct way to check a boolean is `cmpb $0` or `testb $0xff`, whereas a
> lot of our entry code uses `testb $1`. This will work in principle for values
> which are really C _Bool types, but won't work for other integer types which
> are intended to have boolean properties.
>
> cmp is the more logical way of thinking about the operation, so adjust all
> outstanding uses of `testb $1` against boolean values. Changing test to cmp
> changes the logical mnemonic of the following condition from 'zero' to
> 'equal', but the actual encoding remains the same.
>
> No functional change, as all uses are real C _Bool types, and confirmed by
> diffing the disassembly.
>
> Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Wei Liu <wei.liu2@citrix.com>
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next prev parent reply other threads:[~2018-03-02 17:32 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-02-27 14:50 [PATCH v2 0/5] x86: Lift create_exception_frame() up out of C Andrew Cooper
2018-02-27 14:50 ` [PATCH v2 1/5] x86/entry: Correct comparisons against boolean variables Andrew Cooper
2018-03-02 16:27 ` Jan Beulich
2018-03-02 17:32 ` Wei Liu [this message]
2018-02-27 14:50 ` [PATCH v2 2/5] x86/pv: Drop int80_bounce from struct pv_vcpu Andrew Cooper
2018-02-27 14:50 ` [PATCH v2 3/5] x86/pv: Introduce pv_create_exception_frame() Andrew Cooper
2018-03-02 16:44 ` Jan Beulich
2018-02-27 14:50 ` [PATCH v2 4/5] x86/pv: Drop {compat_, }create_bounce_frame() and use the C version instead Andrew Cooper
2018-03-05 9:27 ` Jan Beulich
2018-09-07 14:17 ` Andrew Cooper
2018-09-07 15:49 ` Jan Beulich
2018-02-27 14:50 ` [PATCH v2 5/5] x86/pv: Implement the failsafe callback using the general path Andrew Cooper
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