linux-kernel - Re: [PATCH] x86/alternatives: Fix alt_max

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Date:   Thu, 5 Oct 2017 14:35:33 +0200
From:   Mathias Krause <minipli@...glemail.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, Borislav Petkov <bp@...e.de>,
        x86-ml <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Michael Matz <matz@...e.de>
Subject: Re: [PATCH] x86/alternatives: Fix alt_max_short macro to really be a max()

On 5 October 2017 at 09:58, Mathias Krause <minipli@...glemail.com> wrote:
> On 5 October 2017 at 09:38, Borislav Petkov <bp@...en8.de> wrote:
>> On Wed, Oct 04, 2017 at 08:08:12PM +0200, Mathias Krause wrote:
>>> diff --git a/arch/x86/include/asm/alternative.h b/arch/x86/include/asm/alternative.h
>>> index c096624137ae..7c553f48f163 100644
>>> --- a/arch/x86/include/asm/alternative.h
>>> +++ b/arch/x86/include/asm/alternative.h
>>> @@ -106,9 +106,9 @@ static inline int alternatives_text_reserved(void *start, void *end)
>>>   * max without conditionals. Idea adapted from:
>>       ^^^^^^^^^^^^^^^^^^^^^^^^^
>>
>> You did read this part, right?

Oh, btw., quoting its counter part from arch/x86/include/asm/alternative-asm.h:

/*
 * max without conditionals. Idea adapted from:
 * http://graphics.stanford.edu/~seander/bithacks.html#IntegerMinOrMax
 */
#define alt_max_short(a, b) ((a) ^ (((a) ^ (b)) & -(-((a) < (b)))))

Note the "<"! ...comment is wrong, though the implementation works!

Cheers,
Mathias