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Re: RFC: Should x86-64 support arbitrary calling conventions?
- From: Zack Weinberg <zackw at panix dot com>
- To: "H.J. Lu" <hjl dot tools at gmail dot com>
- Cc: GNU C Library <libc-alpha at sourceware dot org>
- Date: Thu, 23 Mar 2017 17:17:20 -0400
- Subject: Re: RFC: Should x86-64 support arbitrary calling conventions?
- Authentication-results: sourceware.org; auth=none
- References: <CAMe9rOoLSU=zfhdS1DqKQVr-5Hr9jqBjoR_CMUyFHQ8JKJfwZw@mail.gmail.com>
On Thu, Mar 16, 2017 at 6:07 PM, H.J. Lu <hjl.tools@gmail.com> wrote:
> According to x86-64 psABI, xmm0-xmm7 can be used to pass function
> parameters. But ICC also uses xmm8-xmm15 to pass function parameters.
> This doesn't work with newer glibc since _dl_runtime_resolve only preserves
> the first 8 vector registers:
I don't understand why it's necessary for _dl_runtime_resolve to touch
the vector registers _at all_. It's called from a PLT stub, so it has
to be careful to preserve all the integer registers including the
usually-call-clobbered ones, but shouldn't it be able to do all of its
work without disturbing the floating point and vector registers?
zw