Messages in this thread | | | From | Huacai Chen <> | Date | Tue, 18 Oct 2022 10:24:36 +0800 | Subject | Re: [PATCH V2] LoongArch: Add unaligned access support |
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Hi, David,
On Mon, Oct 17, 2022 at 8:58 PM David Laight <David.Laight@aculab.com> wrote: > > From: Huacai Chen > > Sent: 17 October 2022 03:24 > > > > 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. > > > ... > > + /* > > + * This load never faults. > > + */ > > + __get_inst(&insn.word, pc, user); > > On what basis does it never fault? > Any user access can fault. > If nothing else another thread of the process can unmap > the page. Yes, this can happen, since __get_inst() handles fault, we can just remove the comment.
> > > + if (user && !access_ok(addr, 8)) > > + goto sigbus; > > Surely that is technically wrong - a two or four byte > access is valid right at the end of valid user addreeses. Yes, this check should be moved to each case.
> > > + > > + if (insn.reg2i12_format.opcode == ldd_op || > > + insn.reg2i14_format.opcode == ldptrd_op || > > + insn.reg3_format.opcode == ldxd_op) { > > + res = unaligned_read(addr, &value, 8, 1); > > That is the most horrid indentation of long lines I've > ever seen. > I'd also guess you can common up some of this code > by looking at the instruction field that include the > transfer width. > > The long elsif list will generate horrid code. > But maybe since you've just taken a fault it really > doesn't matter. > Indeed just emulating in C using byte accesses > it probably fine. I want to keep the assembly, because we can use more efficient methods with the upcoming alternative mechanism.
Huacai > > David > > - > Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK > Registration No: 1397386 (Wales) >
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