machine_is_XXX( )

kernel code 裡面一堆 machine_is_xxx()，讓程式知道現在是 run 在什麼 機器上。
這麼奇怪的 function 也是用很奇怪的 方式 做出來的。

先是..arch/arm/tools/mach-types

# Database of machine macros and numbers
#
# This file is linux/arch/arm/tools/mach-types
#
# Up to date versions of this file can be obtained from:
#
#   http://www.arm.linux.org.uk/developer/machines/download.php
#
# Please do not send patches to this file; it is automatically generated!
# To add an entry into this database, please see Documentation/arm/README,
# or visit:
#
#   http://www.arm.linux.org.uk/developer/machines/?action=new
#
# Last update: Sun Feb 19 14:16:29 2012
#
# machine_is_xxx        CONFIG_xxxx             MACH_TYPE_xxx           number
#
ebsa110                 ARCH_EBSA110            EBSA110                 0
riscpc                  ARCH_RPC                RISCPC                  1
nexuspci                ARCH_NEXUSPCI           NEXUSPCI                3
ebsa285                 ARCH_EBSA285            EBSA285                 4
netwinder               ARCH_NETWINDER          NETWINDER               5
cats                    ARCH_CATS               CATS                    6
tbox                    ARCH_TBOX               TBOX                    7
co285                   ARCH_CO285              CO285                   8
clps7110                ARCH_CLPS7110           CLPS7110                9
archimedes              ARCH_ARC                ARCHIMEDES              10
a5k                     ARCH_A5K                A5K                     11
etoile                  ARCH_ETOILE             ETOILE                  12
lacie_nas               ARCH_LACIE_NAS          LACIE_NAS               13
clps7500                ARCH_CLPS7500           CLPS7500                14
shark                   ARCH_SHARK              SHARK                   15
brutus                  SA1100_BRUTUS           BRUTUS                  16
personal_server         ARCH_PERSONAL_SERVER    PERSONAL_SERVER         17
itsy                    SA1100_ITSY             ITSY                    18
l7200                   ARCH_L7200              L7200                   19
pleb                    SA1100_PLEB             PLEB                    20
integrator              ARCH_INTEGRATOR         INTEGRATOR              21
h3600                   SA1100_H3600            H3600                   22
..

有一堆 support 的列表..

然後..arch/arm/tools/Makefile

#
# linux/arch/arm/tools/Makefile
#
# Copyright (C) 2001 Russell King
#

include/generated/mach-types.h: $(src)/gen-mach-types $(src)/mach-types
        @echo '  Generating $@'
        @mkdir -p $(dir $@)
        $(Q)$(AWK) -f $^ > $@ || { rm -f $@; /bin/false; }

叫 AWK script : gen-mach-types來處理 mach-types 這個檔案。
產生 : include/generated/mach-types.h

/*
 * This was automagically generated from arch/arm/tools/mach-types!
 * Do NOT edit
 */

#ifndef __ASM_ARM_MACH_TYPE_H
#define __ASM_ARM_MACH_TYPE_H

#ifndef __ASSEMBLY__
/* The type of machine we're running on */
extern unsigned int __machine_arch_type;
#endif

/* see arch/arm/kernel/arch.c for a description of these */
#define MACH_TYPE_EBSA110              0
#define MACH_TYPE_RISCPC               1
#define MACH_TYPE_NEXUSPCI             3
#define MACH_TYPE_EBSA285              4
#define MACH_TYPE_NETWINDER            5
#define MACH_TYPE_CATS                 6
#define MACH_TYPE_TBOX                 7
#define MACH_TYPE_CO285                8
#define MACH_TYPE_CLPS7110             9
#define MACH_TYPE_ARCHIMEDES           10
#define MACH_TYPE_A5K                  11
#define MACH_TYPE_ETOILE               12
#define MACH_TYPE_LACIE_NAS            13
#define MACH_TYPE_CLPS7500             14
#define MACH_TYPE_SHARK                15
#define MACH_TYPE_BRUTUS               16
#define MACH_TYPE_PERSONAL_SERVER      17
#define MACH_TYPE_ITSY                 18
#define MACH_TYPE_L7200                19
#define MACH_TYPE_PLEB                 20
#define MACH_TYPE_INTEGRATOR           21
#define MACH_TYPE_H3600                22
#define MACH_TYPE_IXP1200              23
.....
#ifdef CONFIG_ARCH_EBSA110
# ifdef machine_arch_type
#  undef machine_arch_type
#  define machine_arch_type     __machine_arch_type
# else
#  define machine_arch_type     MACH_TYPE_EBSA110
# endif
# define machine_is_ebsa110()   (machine_arch_type == MACH_TYPE_EBSA110)
#else
# define machine_is_ebsa110()   (0)
#endif

#ifdef CONFIG_ARCH_RPC
# ifdef machine_arch_type
#  undef machine_arch_type
#  define machine_arch_type     __machine_arch_type
# else
#  define machine_arch_type     MACH_TYPE_RISCPC
# endif
# define machine_is_riscpc()    (machine_arch_type == MACH_TYPE_RISCPC)
#else
# define machine_is_riscpc()    (0)
#endif

#ifdef CONFIG_ARCH_NEXUSPCI
# ifdef machine_arch_type
#  undef machine_arch_type
#  define machine_arch_type     __machine_arch_type
# else
#  define machine_arch_type     MACH_TYPE_NEXUSPCI
# endif
# define machine_is_nexuspci()  (machine_arch_type == MACH_TYPE_NEXUSPCI)
#else
# define machine_is_nexuspci()  (0)
#endif

這樣就產生了所有的 machine_is_xxx()

---

然後就是 bootloader 傳來 machine_arch_type 這個變數： http://r40eubuntu.blogspot.tw/2013/06/machinearchtype-kernel.html