On Wed, Apr 19, 2017 at 12:38 PM, Jeffrey Walton <noloa...@gmail.com> wrote:
> According to [1], I can use ".arch_extension" to enable it. According
> to [2], ".arch_extension" is available in GCC 4.6 and GAS 2.21. My
> version of Linaro provides GCC 4.9.2 and GAS 2.25.90. I can also
> duplicate the issue on GCC113 (compiel farm), which provides GCC 4.8
> and GAS 2.24.
ARM is a little ambiguous. It turns out that arch_extension was added
to the arm (32-bit) port in 2010, but wasn't added to the aarch64
(64-bit) port until 2014.
So you need binutils-2.26 in order to use arch_extension pseudo-op
with the aarch64 toolchain.
Meanwhile, you might try looking at the arm_neon.h header file for
your gcc version. Though it apperas in gcc-4.9.2 there is only a
predefined macro __ARM_FEATURE_CRYPTO that you can use, and nothing
for CRC. GCC 5.x adds a __ARM_FEATURE_CRC32 predefined macro that you
could use.
With gcc 6, the arm_neon.h file uses
#pragma GCC push_options
#pragma GCC target ("+nothing+crypto")
...
#pragma GCC pop_options
to enable crypto support. You can do something similar with crc, you
probably want to use "+onthing+crc" if you only want crc support
enalbed, or "+simd+crc" if you want both simd and crc support enabled
for instance.
The GCC aarch64 port does not use the arch64_extension support in binutils.
I think the linux kernel just puts functions that need crc support in
different files, so that those files can be compiled with crc support
enabled via -mcpu=generic+crc.
Jim
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