在frameworks/base/core/java/android/os/Build.java中定义了class Build类，这个类定义了所有关于产品的参数，例如固件版本号，product 名字，板子名字等等，有些参数会在设置->关于手机中显示。
public class Build {
/** Value used for when a build property is unknown. */
public static final String UNKNOWN = "unknown";
/** Either a changelist number, or a label like "M4-rc20". */
public static final String ID = getString("ro.build.id");
/** A build ID string meant for displaying to the user */
public static final String DISPLAY = getString("ro.build.display.id");
/**a firmware realse */
public static final String FIRMWARE = getString("ro.product.firmware");
/** The name of the overall product. */
public static final String PRODUCT = getString("ro.product.name");
/** The name of the industrial design. */
public static final String DEVICE = getString("ro.product.device");
/** The name of the underlying board, like "goldfish". */
public static final String BOARD = getString("ro.product.board");
/** The name of the instruction set (CPU type + ABI convention) of native code. */
public static final String CPU_ABI = getString("ro.product.cpu.abi");
/** The name of the second instruction set (CPU type + ABI convention) of native code. */
public static final String CPU_ABI2 = getString("ro.product.cpu.abi2");
/** The manufacturer of the product/hardware. */
public static final String MANUFACTURER = getString("ro.product.manufacturer");
/** The brand (e.g., carrier) the software is customized for, if any. */
public static final String BRAND = getString("ro.product.brand");
因此，如果想修改这些参数，只要在修改相关的参数就可以了。例如，如果想修改固件版本号，那么找到定义ro.product.firmware的文件（在我做的项目里，是./device/softwinner/crane-gm-g9/crane_gm_g9.mk），修改成想要的版本号，就可以了。
要注意的是，在重新编译的时候，首先要先删掉./out/target/product/crane-gm-g9/recovery/root/default.prop和./out/target/product/crane-gm-g9/system/build.prop再编译才能生效。否则，这个build不一定能重新编译，因为改的是mk文件本身，而不是.java。