Re: Using the kernel thread pointer on aarch64 (tpidr_el1)

[Zach 1 <zach1.gcc@gmail.com>]

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Thanks, I have filed a Bugzilla report here:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108779.

On Mon, Feb 13, 2023 at 4:43 AM Kyrylo Tkachov <Kyrylo.Tkachov@arm.com>
wrote:

> Hello,
>
> > -----Original Message-----
> > From: Gcc-help <gcc-help-bounces+kyrylo.tkachov=arm.com@gcc.gnu.org>
> > On Behalf Of Zach 1 via Gcc-help
> > Sent: Monday, February 13, 2023 2:04 AM
> > To: gcc-help@gcc.gnu.org
> > Subject: Using the kernel thread pointer on aarch64 (tpidr_el1)
> >
> > Hi,
> >
> > On AArch64, GCC seems to use tpidr_el0 (user-mode accessible) to access
> > the
> > thread pointer for loading thread-local variables by default. I can't
> find
> > any option to change this to tpidr_el1 (or tpidr_el2/tpidr_el3). This is
> > necessary for using thread-local variables in kernel code. Clang has the
> > `-mtp` option for AArch64 (
> > https://clang.llvm.org/docs/ClangCommandLineReference.html#cmdoption-
> > clang-mtp)
> > that controls this, but it seems GCC does not? Does any such option
> exist,
> > and if not is there any chance to add support for it? Thanks for any
> help.
>
> Looks like this exists for AArch32 (the arm port of GCC):
> https://gcc.gnu.org/onlinedocs/gcc/ARM-Options.html
>
> AArch64 doesn't support but I suppose it wouldn't be hard to add given arm
> supports it and clang as well.
> Could you file a bug report in Bugzilla to keep track of the request
> please?
>
> Thanks,
> Kyrill
>
> >
> > Zach
>