linux-kernel - Re: [PATCH] arm: Add condition code check to SWP emulator

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Message-ID: <CAHkRjk4QZxoVmCsB1A3DVb5_WCUvN5NfbYz8PNL_7np7+wHGzQ@mail.gmail.com>
Date:	Sun, 20 Nov 2011 10:55:28 +0000
From:	Catalin Marinas <catalin.marinas@....com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	Stepan Moskovchenko <stepanm@...eaurora.org>,
	linux-kernel@...r.kernel.org, bryanh@...eaurora.org,
	David Brown <davidb@...eaurora.org>,
	Leif Lindholm <leif.lindholm@....com>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] arm: Add condition code check to SWP emulator

On 20 November 2011 08:41, Russell King - ARM Linux
<linux@....linux.org.uk> wrote:
> On Sat, Nov 19, 2011 at 05:04:30PM -0800, Stepan Moskovchenko wrote:
>> +static int check_condition(struct pt_regs *regs, unsigned int insn)
>> +{
>> +     unsigned int base_cond, neg, cond = 0;
>> +     unsigned int cpsr_z, cpsr_c, cpsr_n, cpsr_v;
>> +
>> +     cpsr_n = (regs->ARM_cpsr & PSR_N_BIT) ? 1 : 0;
>> +     cpsr_z = (regs->ARM_cpsr & PSR_Z_BIT) ? 1 : 0;
>> +     cpsr_c = (regs->ARM_cpsr & PSR_C_BIT) ? 1 : 0;
>> +     cpsr_v = (regs->ARM_cpsr & PSR_V_BIT) ? 1 : 0;
>> +
>> +     /* Upper 3 bits indicate condition, lower bit incicates negation */
>> +     base_cond = insn >> 29;
>> +     neg = insn & BIT(28) ? 1 : 0;
>> +
>> +     switch (base_cond) {
>> +     case 0x0:       /* equal */
>> +             cond = cpsr_z;
>> +             break;
>> +
>> +     case 0x1:       /* carry set */
>> +             cond = cpsr_c;
>> +             break;
>> +
>> +     case 0x2:       /* minus / negative */
>> +             cond = cpsr_n;
>> +             break;
>> +
>> +     case 0x3:       /* overflow */
>> +             cond = cpsr_v;
>> +             break;
>> +
>> +     case 0x4:       /* unsigned higher */
>> +             cond = (cpsr_c == 1) && (cpsr_z == 0);
>> +             break;
>> +
>> +     case 0x5:       /* signed greater / equal */
>> +             cond = (cpsr_n == cpsr_v);
>> +             break;
>> +
>> +     case 0x6:       /* signed greater */
>> +             cond = (cpsr_z == 0) && (cpsr_n == cpsr_v);
>> +             break;
>> +
>> +     case 0x7:       /* always */
>> +             cond = 1;
>> +             break;
>> +     };
>> +
>> +     return cond && !neg;
>
> There's a much better algorithm to check this.  See the bottom of
> arch/arm/nwfpe/fpopcode.c.
>
> It would probably be best for there to be a common function for doing
> this kind of check, rather than having several implementations of it
> scattered around the kernel.

That's what Leif started doing.

-- 
Catalin
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