How to save and restore a symbol value in Aarch64?

[Jeffrey Walton]

On Thu, Apr 20, 2017 at 8:35 AM, Jiong Wang <jiong.wang@foss.arm.com> wrote:
> On 20/04/17 11:54, Jeffrey Walton wrote:
>>
>> ...
>
> It will not work as you expected.
> They are simply treating "push/pop" as symbols, and their value will be the
> string ".cpu".
>
>
> Below is a purely work around for your reference that you can escape
> assembler's architecture requirement check.
>
> __inline unsigned int GCC_INLINE_ATTRIB
> CRC32B(unsigned int crc, unsigned char v)
> {
>         unsigned int r;
>         asm (
>                         "\t.set raw_x0, 0\n"
>                         "\t.set raw_x1, 1\n"
>                         "\t.set raw_x2, 2\n"
>                         "\t.set raw_x3, 3\n"
>                         "\t.set raw_x4, 4\n"
>                         "\t.set raw_x5, 5\n"
>                         "\t.set raw_x6, 6\n"
>                         "\t.set raw_x7, 7\n"
>                         "\t#crc32w %w2, %w1, %w0\n"
>                         "\t.inst\t0x1ac04800 | (raw_%2) | (raw_%1 << 5) |
> (raw_%0 << 16)\n"
>                         : "=r"(r) : "r"(crc), "r"((unsigned int)v)
>             );
>         return r;
> }

Thanks again Jiong. I needed one small change to make things work. I'm
posting it back to the list in case someone copies/pastes. The
operands needed to be reversed:

__inline unsigned int GCC_INLINE_ATTRIB
CRC32B(unsigned int crc, unsigned char v)
{
    volatile unsigned int res;
    asm (
         "\t" ".set reg_x0, 0\n"
         "\t" ".set reg_x1, 1\n"
         "\t" ".set reg_x2, 2\n"
         "\t" ".set reg_x3, 3\n"
         "\t" ".set reg_x4, 4\n"
         "\t" ".set reg_x5, 5\n"
         "\t" ".set reg_x6, 6\n"
         "\t" ".set reg_x7, 7\n"
         "\t" "#crc32w %w0, %w1, %w2\n"
         "\t" ".inst 0x1ac04800 | (reg_%2 << 16) | (reg_%1 << 5) | (reg_%0)\n"
         : "=r"(res) : "r"(crc), "r"(val)
    );
    return res;
}

Thanks again.

Jeff