Re: [PATCH v8 00/12] Add LoongArch support.

[程璐璐 <chenglulu@loongson.cn>]

在 2022/3/15 下午10:35, Xi Ruoyao 写道:
> On Fri, 2022-03-04 at 15:17 +0800, xuchenghua@loongson.cn wrote:
>
>> v7 -> v8
>> 1. Add new addressing type ADDRESS_REG_REG support.
>> 2. Modify documentation.
>> 3. Eliminate compile-time warnings.
> Hi,
>
> The v8 series does not build LoongArch Linux kernel tree
> (https://github.com/loongson/linux, loongarch-next branch) successfully.
> This is a regression: the v7 series built the kernel fine.
>
> A testcase reduced from the __get_data_asm macro in uaccess.h:
>
> $ cat t1.c
> char *ptr;
> int offset;
> struct m
> {
>    char a[2];
> };
>
> char
> x (void)
> {
>    char t;
>    asm volatile("ld.b %0, %1" : "=r"(t) : "o"(*(struct m *)(ptr + offset)));
>    return t;
> }
>
> $ ./gcc/cc1 t1.c -nostdinc -O
> t1.c: In function ‘x’:
> t1.c:12:3: error: impossible constraint in ‘asm’
>     12 |   asm volatile("ld.b %0, %1" : "=r"(t) : "o"(*(struct m *)(ptr + offset)));
>        |   ^~~
>
> It seems changing the constraint "o" to "m" can work around this issue.
> I'm not sure if this is a compiler bug or a kernel bug.

Hi,

LoongArch supports memory modes as follows:

          mode                    memory constraint

1. base  + index "k"

2. base + imm12 "m"

3. base + imm16 (immediate 4-byte alignment) "ZC"

4. base + 0 "ZB"

so, this constraint should be "m".