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From: Segher Boessenkool <segher@kernel.crashing.org>
To: Sandipan Das <sandipan@linux.ibm.com>
Cc: mpe@ellerman.id.au, paulus@samba.org,
	naveen.n.rao@linux.vnet.ibm.com, linuxppc-dev@lists.ozlabs.org,
	anton@samba.org, ravi.bangoria@linux.ibm.com
Subject: Re: [PATCH 6/6] powerpc sstep: Add modsd, modud instruction emulation
Date: Tue, 4 Sep 2018 16:21:09 -0500	[thread overview]
Message-ID: <20180904212109.GP24439@gate.crashing.org> (raw)
In-Reply-To: <15e572f61bb5c74b01210b9245ce2750a31d6002.1535609090.git.sandipan@linux.ibm.com>

On Mon, Sep 03, 2018 at 08:49:38PM +0530, Sandipan Das wrote:
> +#ifdef __powerpc64__
> +		case 265:	/* modud */
> +			if (!cpu_has_feature(CPU_FTR_ARCH_300))
> +				return -1;
> +			op->val = regs->gpr[ra] % regs->gpr[rb];
> +			goto compute_done;
> +#endif

The mod instruction has special cases that aren't handled by this C code,
too (divide by 0, or signed division of the most negative number by -1).
For the mod intruction the behaviour is undefined in those cases, but you
probably should force some specific behaviour.  You don't want the kernel
to execute a trap instruction, etc. :-)


Segher

  reply	other threads:[~2018-09-04 21:22 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-09-03 15:19 [PATCH 0/6] powerpc sstep: Extend instruction emulation support Sandipan Das
2018-09-03 15:19 ` [PATCH 1/6] powerpc sstep: Add maddhd, maddhdu, maddld instruction emulation Sandipan Das
2018-09-04 22:12   ` Segher Boessenkool
2018-09-05 11:30     ` Sandipan Das
2019-02-20  0:51   ` Michael Ellerman
2018-09-03 15:19 ` [PATCH 2/6] powerpc sstep: Add darn " Sandipan Das
2019-02-20  0:50   ` Michael Ellerman
2019-02-20  9:49     ` Sandipan Das
2018-09-03 15:19 ` [PATCH 3/6] powerpc sstep: Add cnttzw, cnttzd " Sandipan Das
2018-09-04 21:12   ` Segher Boessenkool
2018-09-05  6:36     ` Paul Mackerras
2018-09-03 15:19 ` [PATCH 4/6] powerpc sstep: Add extswsli " Sandipan Das
2018-09-03 15:19 ` [PATCH 5/6] powerpc sstep: Add modsw, moduw " Sandipan Das
2018-09-03 15:19 ` [PATCH 6/6] powerpc sstep: Add modsd, modud " Sandipan Das
2018-09-04 21:21   ` Segher Boessenkool [this message]
2018-09-05 11:53     ` Sandipan Das

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