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SubjectRe: Regression: boot failure on AMD Elan TS-5500
H. Peter Anvin wrote:
> H. Peter Anvin wrote:
>>>>
>>>> startup_32:
>>>> cld
>>>> /* test KEEP_SEGMENTS flag to see if the bootloader is asking
>>>> * us to not reload segments */
>>>> testb $(1<<6), BP_loadflags(%esi)
>>>> jnz 1f
>>>>
>>>> cli
>>>> movl $(__BOOT_DS),%eax
>>>> movl %eax,%ds
>>>> movl %eax,%es
>>>> movl %eax,%fs
>>>> movl %eax,%gs
>>>> movl %eax,%ss
>>>> 1:
>
> On this general subject... I keep thinking that it would be better to
> have this as:
>
> movl %cs, %eax
> addl $8, %eax
> movl %eax, %cs

What's your intent? You can't directly load %cs; do you mean the other
segment registers?

>
> ... instead of a hard-coded constant. That actually removes all
> hard-coded uses of BOOT_CS/BOOT_DS until we eventually load the
> kernel's own boot GDT at head_32.S:94.
>
> Does anyone see any problem with that? As far as I can tell, we're
> requiring %cs == BOOT_CS for the current code anyway (unless
> KEEP_SEGMENTS), but %ds == %cs + 8 seems like a more sensible
> requirement.
>

Oh, you mean

mov %cs, %eax
add $8, %eax
mov %eax, %ds (etc)
?

Seems reasonable.

J



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