How to build the same Linux Kernel twice sources and get the same checksum

I’m searching if it’s possible to build the same Linux Kerneltwice (same sources, same environment, same options, same compiler) and get the same checksum. Anybody knows how to do so?

Answer

The date of build is included in the version, see init version.c :

const char linux_banner[] =
    "Linux version " UTS_RELEASE " (" LINUX_COMPILE_BY "@"
    LINUX_COMPILE_HOST ") (" LINUX_COMPILER ") " UTS_VERSION "n";

and UTS_VERSION is defined in include/linux/compile.h :

/* This file is auto generated, version 1 */
/*  PREEMPT */
#define UTS_MACHINE "arm"
#define UTS_VERSION "#1 PREEMPT Mon Jun 29 10:49:17 CEST 2009"
#define LINUX_COMPILE_TIME "10:49:17"
#define LINUX_COMPILE_BY "cynove"
#define LINUX_COMPILE_HOST "jp"
#define LINUX_COMPILE_DOMAIN "evonyc"
#define LINUX_COMPILER "gcc version 4.3.2 (crosstool-NG-1.4.0) "

compile.h is generated by scripts/mkcompile_h, where you find the following line :

UTS_VERSION="$UTS_VERSION $CONFIG_FLAGS `LC_ALL=C LANG=C date`"

By removing the date from the pervious line, you should be able to get rid of the build time dependency.