linux_precombile.sh

gcc -Wp,-MD,arch/x86/mm/.mmap.o.d  -nostdinc -isystem /usr/lib/gcc/i686-redhat-linux/4.4.6/include -I/home/gan/project/xenomai_prj/linux-2.6.38.8/arch/x86/include -Iinclude  -I/home/gan/project/xenomai_prj/linux-2.6.38.8/include -include include/generated/autoconf.h  -I/home/gan/project/xenomai_prj/linux-2.6.38.8/arch/x86/mm -Iarch/x86/mm -D__KERNEL__ -Wall -Wundef -Wstrict-prototypes -Wno-trigraphs -fno-strict-aliasing -fno-common -Werror-implicit-function-declaration -Wno-format-security -fno-delete-null-pointer-checks -Os -m32 -msoft-float -mregparm=3 -freg-struct-return -mpreferred-stack-boundary=2 -march=i686 -mtune=generic -Wa,-mtune=generic32 -ffreestanding -DCONFIG_AS_CFI=1 -DCONFIG_AS_CFI_SIGNAL_FRAME=1 -DCONFIG_AS_CFI_SECTIONS=1 -pipe -Wno-sign-compare -fno-asynchronous-unwind-tables -mno-sse -mno-mmx -mno-sse2 -mno-3dnow -Wframe-larger-than=2048 -fno-stack-protector -fno-omit-frame-pointer -fno-optimize-sibling-calls -pg -Wdeclaration-after-statement -Wno-pointer-sign -fno-strict-overflow -fconserve-stack -DCC_HAVE_ASM_GOTO    -D"KBUILD_STR(s)=\#s" -D"KBUILD_BASENAME=KBUILD_STR(mmap)"  -D"KBUILD_MODNAME=KBUILD_STR(mmap)" -E /home/gan/project/xenomai_prj/linux-2.6.38.8/arch/x86/mm/mmap.c>mmap.zzz

result.S

page_pde_offset = (__PAGE_OFFSET >> 20);//__PAGE_OFFSET=0xC0000000

/*__brk_base is the begin of page table(页表)
  map from 0~MAPPING_BEYOND_END
  and 0xC0000000 ~ 0xC0000000+MAPPING_BEYOND_END */
	movl $pa(__brk_base), %edi
	movl $pa(initial_page_table), %edx	//initial_page_table is page directory(页目录)
	movl $PTE_IDENT_ATTR, %eax
10:
	leal PDE_IDENT_ATTR(%edi),%ecx		/* Create PDE entry leal指令是获取%edi的地址加PDE_xxx */
	movl %ecx,(%edx)			/* Store identity PDE entry */
	movl %ecx,page_pde_offset(%edx)		/* Store kernel PDE entry */
	addl $4,%edx
	movl $1024, %ecx	//每个页表有1024项页
11:
	/*eax --> es:edi es为前面设置的数据段, edi会自动增加
	它是设置页表项，映射从0开始，每次增长0x1000(1024)*/
	stosl 
	addl $0x1000,%eax
	loop 11b
	/*
	 * End condition: we must map up to the end + MAPPING_BEYOND_END.
	 从下面语句看出MAPPING_BEYOND_END+(_end)是初始化时可以访问的最大地址了
	 $表示获取数值信息
	 */
	movl $pa(_end) + MAPPING_BEYOND_END + PTE_IDENT_ATTR, %ebp
	cmpl %ebp,%eax
	jb 10b
	addl $__PAGE_OFFSET, %edi
	movl %edi, pa(_brk_end)
	shrl $12, %eax
	movl %eax, pa(max_pfn_mapped)	//max_pfn_mapped记录页表的最大值

	/* Do early initialization of the fixmap area */
	movl $pa(initial_pg_fixmap)+PDE_IDENT_ATTR,%eax
	movl %eax,pa(initial_page_table+0xffc)