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Re: [VERY RFC PATCH] x86_64: Rework storing segment registers

From: Luca
Subject: Re: [VERY RFC PATCH] x86_64: Rework storing segment registers
Date: Thu, 15 Jun 2023 20:57:45 +0200

Il 15/06/23 19:41, Sergey Bugaev ha scritto:
On Thu, Jun 15, 2023 at 8:02 PM Luca <luca@orpolo.org> wrote:
That's a bit strange, with my kernel I can now successfully end the
second stage, and without these warnings. Strangely, I don't see the
"Setting up translators: " line...

Check /debootstrap/debootatrap.log :)

The output I posted was from both debootstrap std{out,err} and the
log, interleaved. I'm launching tail -f /debootstrap/debootatrap.log
in parallel with deboostrap itself, following Samuel's instructions.

ah yes, now it makes sense :D I saw that, but then I forgot...

+#if !defined(__x86_64__) || defined(USER32)

I'm wondering if we could simplify this case by defining USER32 also on

Perhaps, but then you'd need to go over the other usages of USER32 and
verify they don't imply x86_64.

from a quick look It seems indeed that most cases assume x86_64. Maybe it would make sense to define USER64 as defined(__x86_64__) && !defined(USER32) since that seems the most common case.

+#if defined(__x86_64__) && !defined(USER32)
+struct i386_saved_fsgs_base_state {
+     unsigned long   fsbase;
+     unsigned long   gsbase;

These can maybe be placed in the i386_machine_state below

Yeah, that'd probably be better.

Why did you remove these? The idea was that they could now be empty on
full 64-bit, and encapsulating the segment handling code for 32-bit,
which is repeated in various places... One addition could also be to set
the kernel segments after saving the user ones, or are there some more
variations of them?

Because there's no longer a need to do anything special for fs/gs,
they are now handled the same way as es/ds, namely ifdef'ed out on

Maybe it would make sense to define new macros like PUSH_SEGS and
POP_SEGS that would push/pop all of (ds, es, fs, gs), but that'd be a
separate change from this patch.

ok, in any case I would keep PUSH_SEGS and SET_KERNEL_SEGMENTS separated, as I think they need to be split in all_intrs.


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