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From: Andrew Cooper <andrew.cooper3@citrix.com>
To: "Roger Pau Monné" <roger.pau@citrix.com>
Cc: Wei Liu <wei.liu2@citrix.com>, Jan Beulich <JBeulich@suse.com>,
	Xen-devel <xen-devel@lists.xen.org>
Subject: Re: [PATCH 5/7] x86/alt: Support for automatic padding calculations
Date: Tue, 13 Feb 2018 10:09:15 +0000	[thread overview]
Message-ID: <f6ef0d0e-5045-3ae1-308e-379cd6568075@citrix.com> (raw)
In-Reply-To: <20180213094501.wskahkozzrkfoayo@MacBook-Pro-de-Roger.local>

On 13/02/2018 09:45, Roger Pau Monné wrote:
> On Mon, Feb 12, 2018 at 11:23:05AM +0000, Andrew Cooper wrote:
>>  .macro ALTERNATIVE oldinstr, newinstr, feature
>>  .L\@_orig_s:
>>      \oldinstr
>>  .L\@_orig_e:
>> +     .skip (-((repl_len(1) - orig_len) > 0) * (repl_len(1) - orig_len)), 0x90
> clang chokes on this expression, because of the negation at the
> beginning and I'm also failing to see why are you adding such
> negation. AFAICT using:
>
> .skip (((repl_len(1) - orig_len) > 0) * (repl_len(1) - orig_len)), 0x90
>
> Is correct: it adds the right padding if the alternative code is
> bigger than the original one, while not adding anything is the
> original code is greater than the alternative one.
>
> The negation just turns the 1 to -1, thus converting the result of the
> whole expression into a negative value.

/sigh so Clang and GAS have different ideas of true.

The reason for this negation is stated in the commit message.  "x > 0"
in GAS yields 0 or -1, rather than the expected 1.

~Andrew

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  reply	other threads:[~2018-02-13 10:09 UTC|newest]

Thread overview: 52+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-02-12 11:23 [PATCH 0/7] x86/alternatives: Support for automatic padding calculations Andrew Cooper
2018-02-12 11:23 ` [PATCH 1/7] x86/alt: Drop unused alternative infrastructure Andrew Cooper
2018-02-12 12:30   ` Wei Liu
2018-02-12 15:56   ` Roger Pau Monné
2018-02-12 15:58     ` Andrew Cooper
2018-02-13 14:22   ` Jan Beulich
2018-02-13 14:41     ` Andrew Cooper
2018-02-13 15:33       ` Jan Beulich
2018-02-14 10:02       ` Jan Beulich
2018-02-12 11:23 ` [PATCH 2/7] x86/alt: Clean up struct alt_instr and its users Andrew Cooper
2018-02-12 12:30   ` Wei Liu
2018-02-12 16:52   ` Roger Pau Monné
2018-02-12 17:18     ` Wei Liu
2018-02-12 17:53       ` Andrew Cooper
2018-02-13 14:26   ` Jan Beulich
2018-02-21 21:22   ` Konrad Rzeszutek Wilk
2018-02-12 11:23 ` [PATCH 3/7] x86/alt: Clean up the assembly used to generate alternatives Andrew Cooper
2018-02-12 12:30   ` Wei Liu
2018-02-12 17:26   ` Roger Pau Monné
2018-02-12 17:54     ` Andrew Cooper
2018-02-13 14:37   ` Jan Beulich
2018-02-23 14:03     ` Andrew Cooper
2018-02-23 15:12       ` Jan Beulich
2018-02-23 16:24         ` Andrew Cooper
2018-02-23 17:28           ` Jan Beulich
2018-02-12 11:23 ` [PATCH 4/7] x86/asm: Remove opencoded uses of altinstruction_entry Andrew Cooper
2018-02-12 12:30   ` Wei Liu
2018-02-12 12:34     ` Andrew Cooper
2018-02-13  9:56     ` Jan Beulich
2018-02-13 10:07       ` Andrew Cooper
2018-02-13 11:10         ` Jan Beulich
2018-02-12 12:52   ` Wei Liu
2018-02-12 17:46   ` Roger Pau Monné
2018-02-12 17:59     ` Andrew Cooper
2018-02-14  9:53   ` Jan Beulich
2018-02-12 11:23 ` [PATCH 5/7] x86/alt: Support for automatic padding calculations Andrew Cooper
2018-02-12 14:39   ` Wei Liu
2018-02-12 15:04     ` Andrew Cooper
2018-02-12 18:41       ` Roger Pau Monné
2018-02-12 18:45         ` Andrew Cooper
2018-02-12 18:09   ` Roger Pau Monné
2018-02-13  9:45   ` Roger Pau Monné
2018-02-13 10:09     ` Andrew Cooper [this message]
2018-02-13 10:26       ` Roger Pau Monné
2018-02-14  9:46   ` Jan Beulich
2018-02-12 11:23 ` [PATCH 6/7] x86/alt: Drop explicit padding of origin sites Andrew Cooper
2018-02-12 14:39   ` Wei Liu
2018-02-12 18:12   ` Roger Pau Monné
2018-02-14  9:53   ` Jan Beulich
2018-02-12 11:23 ` [PATCH 7/7] x86/build: Use new .nop directive when available Andrew Cooper
2018-02-12 14:40   ` Wei Liu
2018-02-13 11:08   ` Roger Pau Monné

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