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>
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> On 16. Jul 2021, at 04:06, Mark Millard <marklmi@yahoo.com> wrote: >=20 >=20 >=20 > On 2021-Jul-15, at 17:40, Michael Tuexen <tuexen at freebsd.org> = wrote: >=20 >> Dear all, >>=20 >> register x18 seems to be special. What is it used for in FreeBSD? >>=20 >> Best regards >> Michael >=20 > = https://developer.arm.com/documentation/den0024/a/The-ABI-for-ARM-64-bit-A= rchitecture/Register-use-in-the-AArch64-Procedure-Call-Standard/Parameters= -in-general-purpose-registers >=20 > reports: >=20 > QUOTE > =E2=80=A2 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 >=20 > 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 >=20 > =3D=3D=3D > Mark Millard > marklmi at yahoo.com > ( dsl-only.net went > away in early 2018-Mar) >=20
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