Hi, in the linux initialization, inside setup_arch, I see ld_mmu_srmmu() (I'm working on SPARC architecture, SRMMU is Sparc Reference MMU) and it comprises many macro calls starting with BTFIXUP... The first two lines look like this BTFIXUPSET_SIMM13(pgdir_shift, SRMMU_PGDIR_SHIFT); // ___ss_pgdir_shift <-- "first line" BTFIXUPSET_SETHI(pgdir_size, SRMMU_PGDIR_SIZE); // ___hs_pgdir_size ... The macro in the first line BTFIXUPSET_SIMM13 is expanded to #define BTFIXUPSET_SIMM13(__name, __val do { ___ss_##__name[0] |= 1; ___ss_##__name[1] = (unsigned)__val; } while (0) So the first line just becomes ___ss_pgdir_shift[0] |= 1; ___ss_pgdir_shift[1] = (unsigned)SRMMU_PGDIR_SHIFT; I looked up __ss_pgdir_shift, and found it's in arch/sparc/boot/btfix.S, ___ss_pgdir_shift: .word 0x73000000,0,68 .word _stext+0x000148c8,0,_stext+0x00014c94,0,_stext+0x00015348,0,_stext+0x00016310,0,_stext+0x000163c8,0,_stext+0x00016fb4,0,_stext+0x00017508,0,_stext+0x0007c31c,0,_stext+0x0007c9b0,0,_stext+0x0007da94,0,_stext+0x0007e310,0,_stext+0x0007edbc,0,_stext+0x0007f058,0,_stext+0x0007f234,0,_stext+0x0007f950,0,_stext+0x0007fbb4,0,_stext+0x00080408,0,_stext+0x00084540,0,_stext+0x00084c30,0,_stext+0x00085a60,0,_stext+0x00086598,0,_stext+0x00087b40,0,_stext+0x00087ce4,0,_stext+0x00088c54,0,_stext+0x00089f58,0,_stext+0x0008d748,0,_stext+0x003d08f4,0,__init_begin+0x0000659c,0,__init_begin+0x00007ac8,0,__init_begin+0x00008088,0,__init_begin+0x00008360,0,__init_begin+0x00008720,0,__init_begin+0x00008908,0,__init_begin+0x00008bf8,0 I think this assembly code was built before the compilation of ld_mmu_srmmu. (this BTFIXUP thing sounds like related to what is called pre-link, I saw it on the web) and This ld_mmu_srmmu function seems to setup general sparc functions and values into those for specific sparc sub-architectures. (replacing genearal things with more specific things) So the first line is setting bit 0 of 0x73000000 and overwriting SRMMU_PGIDR_SHIFT (=2^24) at the next word. and there is a number 68 and it is followed by 68 words. I can see it looks like setting up a page directory table with certain length. But how has this assembly been built during pre-link? Is there any good reference I can read? And Where and how are this values and functions used? Could somebody give me any answer? Sorry for many hasty questions. Best regards, Chan