Messages in this thread | | | From | David Laight <> | Subject | RE: [PATCH V2] LoongArch: Add unaligned access support | Date | Mon, 17 Oct 2022 12:58:25 +0000 |
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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.
> + 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.
> + > + 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.
David
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