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Re: [PATCH] access gdtdesc on segment 0 unconditionally (Re: [PATCH] i38
From: |
Robert Millan |
Subject: |
Re: [PATCH] access gdtdesc on segment 0 unconditionally (Re: [PATCH] i386-qemu port) |
Date: |
Mon, 22 Jun 2009 22:52:13 +0200 |
User-agent: |
Mutt/1.5.18 (2008-05-17) |
On Mon, Jun 22, 2009 at 03:39:03PM -0400, Pavel Roskin wrote:
> On Mon, 2009-06-22 at 11:52 +0200, Robert Millan wrote:
> > > Since %cs is pointing to the code, it should be possible to point it to
> > > gdtdesc. They should be nearby.
> >
> > It is nearby, but the address reference for `gdtdesc' is absolute, NOT
> > relative to %cs. Of course, when %cs is 0 that's no problem. But in my
> > case I can't set %cs to 0 because my code is above 0x10000.
>
> I think we can remove ADDR32 from the command. I tried that on i386-pc
> and it works in qemu and on real hardware. I don't see any need to use
> a 32-bit address in the lgdt command.
This won't build. I don't think it's possible to use relative addresses
with this particular instruction. "DATA32 lgdt %cs:gdtdesc" results in:
boot_img-boot_i386_qemu_boot.o: In function `real_to_prot':
(.text+0x64): relocation truncated to fit: R_386_16 against `.text'
What's the problem with removing %cs? It's presence there is bogus. It
*seems* to indicate gdtdesc is a segment-relative reference, but in fact
it's not, and it just happens to work because %cs was set to 0.
Note: "ADDR32 lgdt %cs:gdtdesc" builds, but generates an absolute address
too.
--
Robert Millan
The DRM opt-in fallacy: "Your data belongs to us. We will decide when (and
how) you may access your data; but nobody's threatening your freedom: we
still allow you to remove your data and not access it at all."
- [PATCH] swap real_to_prot() and prot_to_real() (Re: [PATCH] i386-qemu port), (continued)
- [PATCH] swap real_to_prot() and prot_to_real() (Re: [PATCH] i386-qemu port), Robert Millan, 2009/06/21
- Re: [PATCH] i386-qemu port, Robert Millan, 2009/06/21
- [PATCH] access gdtdesc on segment 0 unconditionally (Re: [PATCH] i386-qemu port), Robert Millan, 2009/06/21
- Re: [PATCH] access gdtdesc on segment 0 unconditionally (Re: [PATCH] i386-qemu port), Pavel Roskin, 2009/06/21
- Re: [PATCH] access gdtdesc on segment 0 unconditionally (Re: [PATCH] i386-qemu port), Robert Millan, 2009/06/22
- Re: [PATCH] access gdtdesc on segment 0 unconditionally (Re: [PATCH] i386-qemu port), Pavel Roskin, 2009/06/22
- Re: [PATCH] access gdtdesc on segment 0 unconditionally (Re: [PATCH] i386-qemu port),
Robert Millan <=
- Re: [PATCH] access gdtdesc on segment 0 unconditionally (Re: [PATCH] i386-qemu port), Robert Millan, 2009/06/22
- Re: [PATCH] access gdtdesc on segment 0 unconditionally (Re: [PATCH] i386-qemu port), Pavel Roskin, 2009/06/22
- Re: [PATCH] access gdtdesc on segment 0 unconditionally (Re: [PATCH] i386-qemu port), Robert Millan, 2009/06/22
- Re: [PATCH] access gdtdesc on segment 0 unconditionally (Re: [PATCH] i386-qemu port), Pavel Roskin, 2009/06/22
- Re: [PATCH] access gdtdesc on segment 0 unconditionally (Re: [PATCH] i386-qemu port), Robert Millan, 2009/06/23
- Re: [PATCH] access gdtdesc on segment 0 unconditionally (Re: [PATCH] i386-qemu port), Pavel Roskin, 2009/06/22
- Re: [PATCH] access gdtdesc on segment 0 unconditionally (Re: [PATCH] i386-qemu port), Robert Millan, 2009/06/22
- about Apple compiler (Re: [PATCH] access gdtdesc on segment 0 unconditionally (Re: [PATCH] i386-qemu port)), Robert Millan, 2009/06/22
- Re: about Apple compiler (Re: [PATCH] access gdtdesc on segment 0 unconditionally (Re: [PATCH] i386-qemu port)), Pavel Roskin, 2009/06/22
[PATCH] s/GRUB_MEMORY_MACHINE_LINK_ADDR/GRUB_KERNEL_MACHINE_LINK_ADDR/g (Re: [PATCH] i386-qemu port), Robert Millan, 2009/06/22