/usr/lib/rpm/macros                rpm-4.8.0 

/usr/lib/rpm/%{_target}/macros      rpm-4.8.0    

/usr/lib/rpm/redhat/macros  redhat-rpm-config-9.0.3 

/etc/rpm/macros.*   centos-release

[/usr/lib/rpm/macros]

# ---- per-platform macros.

#   Macros that are specific to an individual platform. The values here

#   will be used if the per-platform macro file does not exist..

%_arch          x86_64

%_build_arch    x86_64

%_vendor        redhat

%_os            linux

%_gnu           -gnu

%_target_platform   %{_target_cpu}-%{_vendor}-%{_target_os}%{?_gnu}

# ---- config.guess platform macros.

#   Macro(s) similar to the tokens used by configure.

%_host          x86_64-redhat-linux-gnu

%_host_alias    x86_64-redhat-linux-gnu%{nil}

%_host_cpu      x86_64

%_host_vendor   redhat

%_host_os       linux

%_build         %{_host}

%_build_alias   %{_host_alias}

%_build_cpu     %{_host_cpu}

%_build_vendor  %{_host_vendor}

%_build_os      %{_host_os}

%_target        %{_host}

%_target_alias  %{_host_alias}

%_target_cpu    %{_host_cpu}

%_target_vendor %{_host_vendor}

%_target_os     %{_host_os}

[/usr/lib/rpm/platform/x86_64-linux/macros]

%_arch           x86_64

%_vendor         redhat

%_os             linux

%_gnu               -gnu

%_target_platform   %{_target_cpu}-%{_vendor}-%{_target_os}

%optflags           -O2 -g

%__isa_name         x86

%__isa_bits         64

%__isa              %{__isa_name}-%{__isa_bits}

[/usr/lib/rpm/platform/noarch-linux/macros]

%_arch           noarch

%_vendor         redhat

%_os             linux

%_gnu               -gnu

%_target_platform   %{_target_cpu}-%{_vendor}-%{_target_os}

[/usr/lib/rpm/redhat/macros]

%_vendor        redhat

%_os            linux

%_target_platform   %{_target_cpu}-%{_vendor}-%{_target_os}%{?_gnu}

【Specifying target triplets】

Autoconf-generated configure scripts can make decisions based on a canonical name for the system type, or target triplet, which has the form: ‘cpu-vendor-os’, where os can be ‘system’ or ‘kernel-system’

configure can  guess the canonical name for the type of system it‘s running on. To do so it runs a script called config.guess, which infers the name using the uname command or symbols predefined by the C preprocessor.

Alternately, the user can specify the system type with command line arguments to configure (see System Type. Doing so is necessary when cross-compiling. In the most complex case of cross-compiling, three system types are involved. The options to specify them are:

--build=build-type

the type of system on which the package is being configured and compiled. It defaults to the result of running config.guess. 

--host=host-type

the type of system on which the package runs. By default it is the same as the build machine. Specifying it enables the cross-compilation mode.    

--target=target-type

the type of system for which any compiler tools in the package produce code (rarely needed). By default, it is the same as host.

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