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

[Andi Kleen <ak@xxxxxxx>]

> +     /* 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 ?


> +/*
> + * 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.

> + * __xen_guest information
> + */
> +.macro utoa value
> + .if (\value) < 0 || (\value) >= 0x10
> +     utoa (((\value)>>4)&0x0fffffff)
> + .endif
> + .if ((\value) & 0xf) < 10
> +  .byte '0' + ((\value) & 0xf)
> + .else
> +  .byte 'A' + ((\value) & 0xf) - 10
> + .endif
> +.endm

Interesting macro abuse.

-Andi

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