2410的linux內(nèi)核啟動地址30008000 由來探討

內(nèi)核編譯鏈接過程是依靠vmlinux.lds文件，以arm為例vmlinux.lds文件位于kernel/arch/arm/vmlinux.lds，

vmlinux-armv.lds的生成過程在kernel/arch/arm/Makefile中

ifeq ($(CONFIG_CPU_32),y)
PROCESSOR = armv
TEXTADDR = 0xC0008000
LDSCRIPT = arch/arm/vmlinux-armv.lds.in
endif

arch/arm/vmlinux.lds: $(LDSCRIPT) dummy
@sed 's/TEXTADDR/$(TEXTADDR)/;s/DATAADDR/$(DATAADDR)/' $(LDSCRIPT) >$@

查看arch/arm/vmlinux.lds 中

OUTPUT_ARCH(arm)
ENTRY(stext)
SECTIONS
{
. = 0xC0008000;
.init : { /* Init code and data */
_stext = .;
__init_begin = .;
*(.text.init)
__proc_info_begin = .;
*(.proc.info)
__proc_info_end = .;
__arch_info_begin = .;
*(.arch.info)
__arch_info_end = .;
__tagtable_begin = .;
*(.taglist)
__tagtable_end = .;
*(.data.init)
. = ALIGN(16);
__setup_start = .;
*(.setup.init)
__setup_end = .;
__initcall_start = .;
*(.initcall.init)
__initcall_end = .;
. = ALIGN(4096);
__init_end = .;
}

/DISCARD/ : { /* Exit code and data */
*(.text.exit)
*(.data.exit)
*(.exitcall.exit)
}

.text : { /* Real text segment */
_text = .; /* Text and read-only data */
*(.text)
*(.fixup)
*(.gnu.warning)
*(.rodata)
*(.rodata.*)
*(.glue_7)
*(.glue_7t)
*(.got) /* Global offset table */

_etext = .; /* End of text section */
}

.kstrtab : { *(.kstrtab) }

. = ALIGN(16);
__ex_table : { /* Exception table */
__start___ex_table = .;
*(__ex_table)
__stop___ex_table = .;
}

__ksymtab : { /* Kernel symbol table */
__start___ksymtab = .;
*(__ksymtab)
__stop___ksymtab = .;
}

. = ALIGN(8192);

.data : {
/*
* first, the init task union, aligned
* to an 8192 byte boundary.
*/
*(.init.task)

/*
* then the cacheline aligned data
*/
. = ALIGN(32);
*(.data.cacheline_aligned)

/*
* and the usual data section
*/
*(.data)
CONSTRUCTORS

_edata = .;
}

.bss : {
__bss_start = .; /* BSS */
*(.bss)
*(COMMON)
_end = . ;
}
/* Stabs debugging sections. */
.stab 0 : { *(.stab) }
.stabstr 0 : { *(.stabstr) }
.stab.excl 0 : { *(.stab.excl) }
.stab.exclstr 0 : { *(.stab.exclstr) }
.stab.index 0 : { *(.stab.index) }
.stab.indexstr 0 : { *(.stab.indexstr) }
.comment 0 : { *(.comment) }
}

arch/arm/Makefile中：

vmlinux: arch/arm/vmlinux.lds

arch/arm/vmlinux.lds: $(LDSCRIPT) dummy
@sed 's/TEXTADDR/$(TEXTADDR)/;s/DATAADDR/$(DATAADDR)/' $(LDSCRIPT) >$@

MAKEBOOT = $(MAKE) -C arch/$(ARCH)/boot

bzImage zImage zinstall Image bootpImage install: vmlinux
@$(MAKEBOOT) $@

但在kernel/arch/arm/boot/Makefile

ifeq ($(CONFIG_ARCH_S3C2410),y)
ZTEXTADDR = 0x30008000
ZRELADDR = 0x30008000
endif

zImage: $(CONFIGURE) compressed/vmlinux
$(OBJCOPY) -O binary -R .note -R .comment -S compressed/vmlinux $@

compressed/vmlinux: $(TOPDIR)/vmlinux dep
@$(MAKE) -C compressed vmlinux

在compressed目錄下的Makefile中

ZLDFLAGS = -p -X -T vmlinux.lds

SEDFLAGS = s/TEXT_START/$(ZTEXTADDR)/;s/LOAD_ADDR/$(ZRELADDR)/;s/BSS_START/$(ZBSSADDR)/

all: vmlinux

vmlinux: $(HEAD) $(OBJS) piggy.o vmlinux.lds
$(LD) $(ZLDFLAGS) $(HEAD) $(OBJS) piggy.o $(LIBGCC) -o vmlinux

vmlinux.lds: vmlinux.lds.in Makefile $(TOPDIR)/arch/$(ARCH)/boot/Makefile $(TOPDIR)/.config
@sed "$(SEDFLAGS)" vmlinux.lds.in > $@

vmlinux-armv.lds.in文件的內(nèi)容：

OUTPUT_ARCH(arm)
ENTRY(_start)
SECTIONS
{
. = LOAD_ADDR;
_load_addr = .;

. = TEXT_START;
_text = .;

.text : {
_start = .;
*(.start)
*(.text)
*(.fixup)
*(.gnu.warning)
*(.rodata)
*(.rodata.*)
*(.glue_7)
*(.glue_7t)
input_data = .;
piggy.o
input_data_end = .;
. = ALIGN(4);
}

_etext = .;

_got_start = .;
.got : { *(.got) }
_got_end = .;
.got.plt : { *(.got.plt) }
.data : { *(.data) }
_edata = .;

. = BSS_START;
__bss_start = .;
.bss : { *(.bss) }
_end = .;

.stack (NOLOAD) : { *(.stack) }

.stab 0 : { *(.stab) }
.stabstr 0 : { *(.stabstr) }
.stab.excl 0 : { *(.stab.excl) }
.stab.exclstr 0 : { *(.stab.exclstr) }
.stab.index 0 : { *(.stab.index) }
.stab.indexstr 0 : { *(.stab.indexstr) }
.comment 0 : { *(.comment) }
}

vmlinux.lds內(nèi)容為

OUTPUT_ARCH(arm)
ENTRY(_start)
SECTIONS
{
. = 0x30008000;
_load_addr = .;

. = 0;
_text = .;

.text : {
_start = .;
*(.start)
*(.text)
*(.fixup)
*(.gnu.warning)
*(.rodata)
*(.rodata.*)
*(.glue_7)
*(.glue_7t)
input_data = .;
piggy.o
input_data_end = .;
. = ALIGN(4);
}

_etext = .;

_got_start = .;
.got : { *(.got) }
_got_end = .;
.got.plt : { *(.got.plt) }
.data : { *(.data) }
_edata = .;

. = ALIGN(4);
__bss_start = .;
.bss : { *(.bss) }
_end = .;

.stack (NOLOAD) : { *(.stack) }

.stab 0 : { *(.stab) }
.stabstr 0 : { *(.stabstr) }
.stab.excl 0 : { *(.stab.excl) }
.stab.exclstr 0 : { *(.stab.exclstr) }
.stab.index 0 : { *(.stab.index) }
.stab.indexstr 0 : { *(.stab.indexstr) }
.comment 0 : { *(.comment) }
}

一般情況下都在生成vmlinux后，再對內(nèi)核進(jìn)行壓縮成為zImage，壓縮的目錄是kernel/arch/arm/boot。
下載到flash中的是壓縮后的zImage文件，zImage是由壓縮后的vmlinux和解壓縮程序組成，如下圖所示：
|-----------------| |-----------------|
| | | |
| | | decompress code |
| vmlinux | |-----------------| zImage
| | | |
| | | |
| | | |
| | | |
| | /|-----------------|
| | /
| | /
| | /
|-----------------|/

zImage鏈接腳本也叫做vmlinux.lds，位于kernel/arch/arm/boot/compressed。
是由同一目錄下的vmlinux.lds.in文件生成的

在kernel/arch/arm/boot/Makefile文件中定義了：

ifeq ($(CONFIG_ARCH_S3C2410),y)
ZTEXTADDR = 0x30008000
ZRELADDR = 0x30008000
endif

ZTEXTADDR就是解壓縮代碼的ram偏移地址，ZRELADDR是內(nèi)核ram啟動的偏移地址，這里看到指定ZTEXTADDR的地址為30008000，

以上就是我對內(nèi)核啟動地址的分析，總結(jié)一下內(nèi)核啟動地址的設(shè)置：

設(shè)置kernel/arch/arm/boot/Makefile文件中的

ifeq ($(CONFIG_ARCH_S3C2410),y)
ZTEXTADDR = 0x30008000
ZRELADDR = 0x30008000
endif
# We now have a PIC decompressor implementation. Decompressors running
# from RAM should not define ZTEXTADDR. Decompressors running directly
# from ROM or Flash must define ZTEXTADDR (preferably via the config)
#

查看2410的datasheet ,發(fā)現(xiàn)內(nèi)存映射的基址是0x3000 0000 ,那么 0x30008000又是如何來的呢？

在內(nèi)核文檔kernel/Document/arm/Booting 文件中有：

Calling the kernel image

Existing boot loaders: MANDATORY
New boot loaders: MANDATORY

There are two options for calling the kernel zImage. If the zImage is stored in flash, and is linked correctly to be run from flash, then it is legal for the boot loader to call the zImage in flash directly.

The zImage may also be placed in system RAM (at any location) and called there. Note that the kernel uses 16K of RAM below the image to store page tables. The recommended placement is 32KiB into RAM.

看來在image下面用了32K(0x8000)的空間存放內(nèi)核頁表，
0x30008000就是2410的內(nèi)核在RAM中的啟動地址,這個地址就是這么來的。