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Re: How to save and restore a symbol value in Aarch64?

On Thu, Apr 20, 2017 at 8:35 AM, Jiong Wang <> wrote:
> On 20/04/17 11:54, Jeffrey Walton wrote:
>> On Thu, Apr 20, 2017 at 6:02 AM, Andreas Schwab <>
>> wrote:
>>> On Apr 20 2017, Jeffrey Walton <> 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".

OK, thanks. My test case was bad. It needed to use a feature other
than NEON after the CRC. Trying to use AES caused the error I was
looking for.

> 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 Jiong. Wow, I'm fairly certain I would not have gotten that on my own.

If you get to the Baltimore MD or Washington DC area, then dinner and
cold beers are on me.


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