Re: [RFC PATCH 10/35] Add a new head.S start-of-day file for booting on Xen.

[Chris Wright <chrisw@sous-sol.org>]

* Andi Kleen (ak@suse.de) wrote:
> > +	/* get vendor info */
> > +	xorl %eax,%eax			# call CPUID with 0 -> return vendor ID
> > +	cpuid
> > +	movl %eax,X86_CPUID		# save CPUID level
> > +	movl %ebx,X86_VENDOR_ID		# lo 4 chars
> > +	movl %edx,X86_VENDOR_ID+4	# next 4 chars
> > +	movl %ecx,X86_VENDOR_ID+8	# last 4 chars
> > +
> > +	movl $1,%eax		# Use the CPUID instruction to get CPU type
> > +	cpuid
> > +	movb %al,%cl		# save reg for future use
> > +	andb $0x0f,%ah		# mask processor family
> > +	movb %ah,X86
> > +	andb $0xf0,%al		# mask model
> > +	shrb $4,%al
> > +	movb %al,X86_MODEL
> > +	andb $0x0f,%cl		# mask mask revision
> > +	movb %cl,X86_MASK
> > +	movl %edx,X86_CAPABILITY
> 
> Can you make the CPU detection a common subfunction with the normal head.S ?

I don't see why not, prefer to share as much as possible.

> > +/*
> > + * BSS section
> > + */
> > +.section ".bss.page_aligned","w"
> > +ENTRY(swapper_pg_dir)
> > +	.fill 1024,4,0
> > +ENTRY(empty_zero_page)
> > +	.fill 4096,1,0
> > +
> > +/*
> > + * This starts the data section.
> > + */
> > +.data
> > +
> > +	ALIGN
> > +	.word 0				# 32 bit align gdt_desc.address
> > +	.globl cpu_gdt_descr
> > +cpu_gdt_descr:
> > +	.word GDT_SIZE
> > +	.long cpu_gdt_table
> > +
> > +	.fill NR_CPUS-1,8,0		# space for the other GDT descriptors
> > +
> > +/*
> > + * The Global Descriptor Table contains 28 quadwords, per-CPU.
> > + */
> > +	.align PAGE_SIZE_asm
> > +ENTRY(cpu_gdt_table)
> 
> GDT and empty_zero_page should be shared (they're identical right?) Put them into a 
> new separate common file.

There's still kernel/user cs/ds in gdt, so it's not all zero.

thanks,
-chris