Re: RFC: Should x86-64 support arbitrary calling conventions?

[Florian Weimer <fw at deneb dot enyo dot de>]

* Alexander Monakov:

> On Fri, 24 Mar 2017, Florian Weimer wrote:
>> > There are also "foreign calls" in ld.so, where functions in libc.so are
>> > used and vector registers may be cloberred.
>> 
>> Right.  But the _dl_fixup path relevant to the trampoline should not
>> do that much work.  (Not sure if audit modules come into play here.)
>> 
>> The largest problem probably is this: IFUNC resolvers would have to be
>> compiled in that special way, too, and those can reside in
>> applications.
>
> The libc can save vector register as-needed, just before calling
> external code (such as ifunc resolvers and audit callbacks).

Right, that might be a reasonable alternative.

But as I said, the XSAVE-based approach has the advantage that future
CPUs will no longer require glibc changes.  In the past, that has been
a constant source of headaches (both bugs and performance problems).