Date: Fri, 16 Jul 2021 13:08:55 +0200 From: tuexen@freebsd.org To: Mark Millard <marklmi@yahoo.com> Cc: freebsd-arm@freebsd.org Subject: Re: register x18 Message-ID: <32C24DDC-C8A1-43CD-9220-8009B229E452@freebsd.org> In-Reply-To: <BFF3BCE7-3387-4A7C-A71C-890223CDDF18@yahoo.com> References: <86EC9C12-F90C-4D0C-BFA3-41986C9F07B5@freebsd.org> <BFF3BCE7-3387-4A7C-A71C-890223CDDF18@yahoo.com>
index | next in thread | previous in thread | raw e-mail
> On 16. Jul 2021, at 04:06, Mark Millard <marklmi@yahoo.com> wrote: > > > > On 2021-Jul-15, at 17:40, Michael Tuexen <tuexen at freebsd.org> wrote: > >> Dear all, >> >> register x18 seems to be special. What is it used for in FreeBSD? >> >> Best regards >> Michael > > https://developer.arm.com/documentation/den0024/a/The-ABI-for-ARM-64-bit-Architecture/Register-use-in-the-AArch64-Procedure-Call-Standard/Parameters-in-general-purpose-registers > > reports: > > QUOTE > • X18 is the platform register and is reserved for the use of platform ABIs. This is an adional temporary register on platforms that don't assign a special meaning to it. > END QUOTE > > So, special, yes. But I do not know what the "platform ABI" usage > for it might be on FreeBSD. So, for the most part, this does not > well-answer your question. Sorry. Yepp, I found the above text. However, x18 seems to be used when accessing global variables. I am looking at a panic, where the system panics on accessing global variable, which can be controlled by sysctl. It seems that x18 does not have the expected value, but it is also not set in the function... Best regards Michael > > === > Mark Millard > marklmi at yahoo.com > ( dsl-only.net went > away in early 2018-Mar) >home | help
Want to link to this message? Use this
URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?32C24DDC-C8A1-43CD-9220-8009B229E452>