Jeff, the problem is not detecting the CPU type at runtime, the problem is
trying to re-compile the code to take advantage of that CPU at runtime.
depending on what CPU you have the kernel (and compiler) can use different
commands/opmizations/etc, if you want to do this on boot you have two
options.
1. re-compile the kernel
2. change all the CPU specific places from inline code to function calls
into a table that get changed at boot to point at the correct calls.
doing #2 will cost you so much performance that you would be better off
just compiling for a 386 and not going through the autodetect hassle in
the first place.
David Lang
On Tue, 7 Nov 2000, Jeff V. Merkey wrote:
> Date: Tue, 07 Nov 2000 16:10:58 -0700
> From: Jeff V. Merkey <jmerkey@timpanogas.org>
> To: kernel@kvack.org
> Cc: Martin Josefsson <gandalf@wlug.westbo.se>,
> Tigran Aivazian <tigran@veritas.com>, Anil kumar <anils_r@yahoo.com>,
> linux-kernel@vger.kernel.org
> Subject: Re: Installing kernel 2.4
>
>
> There are tests for all this in the feature flags for intel and
> non-intel CPUs like AMD -- including MTRR settings. All of this could
> be dynamic. Here's some code that does this, and it's similiar to
> NetWare. It detexts CPU type, feature flags, special instructions,
> etc. All of this on x86 could be dynamically detected.
>
> :-)
>
> ;*************************************************************************
> ;
> ; check current processor type and state
> ;
> ;*************************************************************************
>
> public DetectProcessorInformation
> DetectProcessorInformation proc near
>
> mov ax, cs
> mov ds, ax
> mov es, ax
>
> pushf
> call get_cpuid
> call get_fpuid
> call print
> popf
> ret
>
> DetectProcessorInformation endp
>
> get_cpuid proc near
>
> check_8086:
>
> pushf
> pop ax
> mov cx, ax
> and ax, 0fffh
> push ax
> popf
> pushf
> pop ax
> and ax, 0f000h
> cmp ax, 0f000h ; flag bits 12-15 are always set on an 8086
> mov CPU_TYPE, 0 ; 8086 detected
> je end_get_cpuid
>
> check_80286:
> or cx, 0f000h
> push cx
> popf
> pushf
> pop ax
> and ax, 0f000h ; flag bits 12-15 are always clear on 80286 in
> real mode
> mov CPU_TYPE, 2 ; 80286 processor
> jz end_get_cpuid
>
> check_80386:
> mov bx, sp
> and sp, not 3
> OPND32
> pushf
> OPND32
> pop ax
> OPND32
> mov cx, ax
> OPND32 35h, 40000h
> OPND32
> push ax
> OPND32
> popf
> OPND32
> pushf
> OPND32
> pop ax
> OPND32
> xor ax, cx ; AC bit won't toggle, 80386 detected
> mov sp, bx
> mov CPU_TYPE, 3 ; 80386 detected
> jz end_get_cpuid
>
> and sp, not 3
> OPND32
> push cx
> OPND32
> popf
> mov sp, bx ; restore stack
>
>
> check_80486:
> mov CPU_TYPE, 4 ; default to 80486
>
> OPND32
> mov ax, cx
> OPND32 35h, 200000h ; xor ID bit
> OPND32
> push ax
> OPND32
> popf
> OPND32
> pushf
> OPND32
> pop ax
> OPND32
> xor ax, cx ; cant toggle ID bit
> je end_get_cpuid
>
>
> check_vendor:
> mov ID_FLAG, 1
> OPND32
> xor ax, ax
> CPUID
> OPND32
> mov word ptr VENDOR_ID, bx
> OPND32
> mov word ptr VENDOR_ID[+4], dx
> OPND32
> mov word ptr VENDOR_ID[+8], cx
> mov si, offset VENDOR_ID
> mov di, offset intel_id
> mov cx, length intel_id
>
> compare:
> repe cmpsb
> or cx, cx
> jnz end_get_cpuid
>
> intel_processor:
> mov INTEL_PROC, 1
>
> cpuid_data:
> OPND32
> cmp ax, 1
>
> jl end_get_cpuid
> OPND32
> xor ax, ax
> OPND32
> inc ax
> CPUID
> mov byte ptr ds:STEPPING, al
> and STEPPING, STEPPING_MASK
>
> and al, MODEL_MASK
> shr al, MODEL_SHIFT
> mov byte ptr ds:CPU_MODEL, al
>
> and ax, FAMILY_MASK
> shr ax, FAMILY_SHIFT
> mov byte ptr ds:CPU_TYPE, al
>
> mov dword ptr FEATURE_FLAGS, edx
>
> end_get_cpuid:
> ret
>
> get_cpuid endp
>
>
> get_fpuid proc near
>
> fninit
> mov word ptr ds:FP_STATUS, 5a5ah
>
> fnstsw word ptr ds:FP_STATUS
> mov ax, word ptr ds:FP_STATUS
> cmp al, 0
>
> mov FPU_TYPE, 0
> jne end_get_fpuid
>
> check_control_word:
> fnstcw word ptr ds:FP_STATUS
> mov ax, word ptr ds:FP_STATUS
> and ax, 103fh
> cmp ax, 3fh
>
> mov FPU_TYPE, 0
> jne end_get_fpuid
> mov FPU_TYPE, 1
>
>
> check_infinity:
> cmp CPU_TYPE, 3
> jne end_get_fpuid
> fld1
> fldz
> fdiv
> fld st
> fchs
> fcompp
> fstsw word ptr ds:FP_STATUS
> mov ax, word ptr ds:FP_STATUS
> mov FPU_TYPE, 2
>
> sahf
> jz end_get_fpuid
> mov FPU_TYPE, 3
> end_get_fpuid:
> ret
> get_fpuid endp
>
>
>
> print proc near
> cmp ID_FLAG, 1
> je print_cpuid_data
>
> if (VERBOSE)
> mov dx, offset id_msg
> call OutputMessage
> endif
>
> print_86:
> cmp CPU_TYPE, 0
> jne print_286
>
> if (VERBOSE)
> mov dx, offset c8086
> call OutputMessage
> endif
> cmp FPU_TYPE, 0
> je end_print
>
> if (VERBOSE)
> mov dx, offset fp_8087
> call OutputMessage
> endif
> jmp end_print
>
> print_286:
> cmp CPU_TYPE, 2
> jne print_386
> if (VERBOSE)
> mov dx, offset c286
> call OutputMessage
> endif
> cmp FPU_TYPE, 0
> je end_print
> if (VERBOSE)
> mov dx, offset fp_80287
> call OutputMessage
> endif
> jmp end_print
>
> print_386:
> cmp CPU_TYPE, 3
> jne print_486
> if (VERBOSE)
> mov dx, offset c386
> call OutputMessage
> endif
> cmp FPU_TYPE, 0
> je end_print
> cmp FPU_TYPE, 2
> jne print_387
> if (VERBOSE)
> mov dx, offset fp_80287
> call OutputMessage
> endif
> jmp end_print
>
> print_387:
> if (VERBOSE)
> mov dx, offset fp_80387
> call OutputMessage
> endif
> jmp end_print
>
> print_486:
> cmp FPU_TYPE, 0
> je print_Intel486sx
> if (VERBOSE)
> mov dx, offset c486
> call OutputMessage
> endif
> jmp end_print
>
> print_Intel486sx:
> if (VERBOSE)
> mov dx, offset c486nfp
> call OutputMessage
> endif
> jmp end_print
>
> print_cpuid_data:
>
> cmp_vendor:
> cmp INTEL_PROC, 1
> jne not_GenuineIntel
>
> cmp CPU_TYPE, 4
> jne check_Pentium
> if (VERBOSE)
> mov dx, offset Intel486_msg
> call OutputMessage
> endif
> jmp print_family
>
> check_Pentium:
> cmp CPU_TYPE, 5
> jne check_PentiumPro
> if (VERBOSE)
> mov dx, offset Pentium_msg
> call OutputMessage
> endif
> jmp print_family
>
> check_PentiumPro:
> cmp CPU_TYPE, 6
> jne print_features
> if (VERBOSE)
> mov dx, offset PentiumPro_msg
> call OutputMessage
> endif
>
> print_family:
>
> IF VERBOSE
> mov dx, offset family_msg
> call OutputMessage
> ENDIF
>
> mov al, byte ptr ds:CPU_TYPE
> mov byte ptr dataCR, al
> add byte ptr dataCR, 30h
>
> IF VERBOSE
> mov dx, offset dataCR
> call OutputMessage
> ENDIF
>
> print_model:
>
> IF VERBOSE
> mov dx, offset model_msg
> call OutputMessage
> ENDIF
>
> mov al, byte ptr ds:CPU_MODEL
> mov byte ptr dataCR, al
> add byte ptr dataCR, 30h
>
> IF VERBOSE
> mov dx, offset dataCR
> call OutputMessage
> ENDIF
>
> print_features:
> mov ax, word ptr ds:FEATURE_FLAGS
> and ax, FPU_FLAG
> jz check_mce
>
> if (VERBOSE)
> mov dx, offset fpu_msg
> call OutputMessage
> ENDIF
>
> check_mce:
> mov ax, word ptr ds:FEATURE_FLAGS
> and ax, MCE_FLAG
> jz check_wc
>
> IF VERBOSE
> mov dx, offset mce_msg
> call OutputMessage
> ENDIF
>
> check_CMPXCHG8B:
> mov ax, word ptr ds:FEATURE_FLAGS
> and ax, CMPXCHG8B_FLAG
> jz check_4MB_paging
>
> IF VERBOSE
> mov dx, offset cmp_msg
> call OutputMessage
> ENDIF
>
> chekc_io_break:
> mov ax, word ptr ds:FEATURE_FLAGS
> test ax, 4
> jz check_4MB_paging
>
> IF VERBOSE
> mov dx, offset io_break_msg
> call OutputMessage
> ENDIF
>
> ; Enable Debugging Extensions bit in CR4
> CR4_TO_ECX
> or ecx, 08h
> ECX_TO_CR4
>
> if (VERBOSE)
> mov dx, offset io_break_enable
> call OutputMessage
> endif
>
> check_4MB_paging:
> mov ax, word ptr ds:FEATURE_FLAGS
> test ax, 08h
> jz check_PageExtend
>
> IF VERBOSE
> mov dx, offset page_4MB_msg
> call OutputMessage
> ENDIF
>
> ; Enable page size extension bit in CR4
> CR4_TO_ECX
> or ecx, 10h
> ECX_TO_CR4
>
> if (VERBOSE)
> mov dx, offset p4mb_enable
> call OutputMessage
> endif
>
> check_PageExtend:
> mov ax, word ptr ds:FEATURE_FLAGS
> test ax, 40h
> jz check_wc
>
> ;; DEBUG DEBUG DEBUG !!!
> ; Enable page address extension bit in CR4
>
> ;; CR4_TO_ECX
> ;; or ecx, 20h
> ;; ECX_TO_CR4
>
> check_wc:
> mov dx, word ptr ds:FEATURE_FLAGS
> test dx, 1000h ; MTRR support flag
> jz end_print
>
> if (VERBOSE)
> mov dx, offset wc_enable
> call OutputMessage
> endif
> jmp end_print
>
> not_GenuineIntel:
> if (VERBOSE)
> mov dx, offset not_Intel
> call OutputMessage
> endif
>
> end_print:
> ret
> print endp
>
>
> kernel@kvack.org wrote:
> >
> > On Tue, 7 Nov 2000, Jeff V. Merkey wrote:
> >
> > > So how come NetWare and NT can detect this at run time, and we have to
> > > use a .config option to specifiy it? Come on guys.....
> >
> > Then run a kernel compiled for i386 and suffer the poorer code quality
> > that comes with not using newer instructions and including the
> > workarounds for ancient hardware.
> >
> > -ben
> >
> > -
> > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> > the body of a message to majordomo@vger.kernel.org
> > Please read the FAQ at http://www.tux.org/lkml/
> -
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
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> Please read the FAQ at http://www.tux.org/lkml/
>
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