is there a way to find the maximum alignment supported by the linker?

[Toby Douglass]

On Sun, Jun 11, 2017 at 10:18 PM, tim prince via gcc-help
<gcc-help@gcc.gnu.org> wrote:
>> Is there a way to find out the maximum alignment supported by the iinker?
>
> You may need to look at the binutils source (if  your gcc uses gnu ld),
> where the maximum supported alignment is defined.

Not documented as such - source code time.  That's okay.

> 32-byte alignment needs
> to be supported for x86-64 platforms beginning with Intel Nehalem; 64-byte
> alignment for those which support AVX512.  So it is a poor quality build of
> binutils which doesn't meet those requirements.   Not many years ago, the
> binutils default on windows was less than 16-byte alignment and so it was
> useful to build your own copy with this corrected, but there may be a limit
> to what the platform can support.  Surely, you can run objdump on your
> executables and see what alignments you get in those spots where you set a
> request.  Agreed that 128-byte alignment on x86 might avoid some situations
> where the prefetcher brings in a useless adjacent cache line, but the cache
> line size is 64 bytes.

I read just a few days ago that Intel x86 (not x86_64) cache line
lengths varied by processor from 32 to 128 bytes.  AFAIK, x86_64 is
always 64 bytes, but I have no strong confirmation of that.  I have
read Intel these days in hardware (sometimes something you can switch
off in the BIOS) always brings over two cache lines at a time, so if
you're trying to isolate a variable from other activity you have to
treat the cache linn size as if it's 128 bytes.

Thanks for your help, Tim!