linux-kernel - RE: [PATCH V3] LoongArch: Add unaligned access support

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Message-ID: <39ea2a6fee654b68974ef38237a61e80@AcuMS.aculab.com>
Date:   Mon, 17 Oct 2022 13:11:24 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Huacai Chen' <chenhuacai@...ngson.cn>,
        Arnd Bergmann <arnd@...db.de>,
        Huacai Chen <chenhuacai@...nel.org>
CC:     "loongarch@...ts.linux.dev" <loongarch@...ts.linux.dev>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
        Xuefeng Li <lixuefeng@...ngson.cn>,
        Guo Ren <guoren@...nel.org>, Xuerui Wang <kernel@...0n.name>,
        Jiaxun Yang <jiaxun.yang@...goat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH V3] LoongArch: Add unaligned access support

From: Huacai Chen
> Sent: 17 October 2022 13:52
> 
> Loongson-2 series (Loongson-2K500, Loongson-2K1000) don't support
> unaligned access in hardware, while Loongson-3 series (Loongson-3A5000,
> Loongson-3C5000) are configurable whether support unaligned access in
> hardware. This patch add unaligned access emulation for those LoongArch
> processors without hardware support.
> 
.....
> +	} else if (insn.reg2i12_format.opcode == fstd_op ||
> +		insn.reg3_format.opcode == fstxd_op) {
> +		value = read_fpr(insn.reg2i12_format.rd);
> +		res = unaligned_write(addr, value, 8);
> +		if (res)
> +			goto fault;
> +	} else if (insn.reg2i12_format.opcode == fsts_op ||
> +		insn.reg3_format.opcode == fstxs_op) {
> +		value = read_fpr(insn.reg2i12_format.rd);
> +		res = unaligned_write(addr, value, 4);
> +		if (res)
> +			goto fault;

Are those right?
Shouldn't something be converting from 'double' to
'float' in there?
And generating SIGFPE (?) if the exponent is out of range.

(And the same for write_fpr().)

	David

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