How to save and restore a symbol value in Aarch64?

[Jiong Wang]

On 20/04/17 11:54, Jeffrey Walton wrote:
> On Thu, Apr 20, 2017 at 6:02 AM, Andreas Schwab <schwab@linux-m68k.org> wrote:
>> On Apr 20 2017, Jeffrey Walton <noloader@gmail.com> wrote:
>>
>>> I need the method to get the previous .cpu value
>> .cpu is not a symbol, it is a directive, so you cannot get its "value".
>> The effect of the directive is to modify the internal state of the
>> assembler, which is not directly accessible to the assembler input.
> Thanks Andreas.
>
> Does '.set push, .cpu' and '.set pop, .cpu' work as {expected|desired}
> for Aarch32 and Aarch64?

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;
}

Regards,
Jiong