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

[Chris Wright <chrisw@xxxxxxxxxxxx>]

* Andi Kleen (ak@xxxxxxx) 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

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