uclinux-2008R1-RC8(bf561)到VDSP5的移植（7）：_sdata

在head.s中，要保存數據段的起始位置，如下所示：

p1.l = __rambase;
p1.h = __rambase;
r0.l = __sdata;
r0.h = __sdata;
[p1] = r0;

在這裡，_sdata是在vmlinux.lds.s中定義的一個值，它指向數據段的首地址，如下所示：

.data :
{
/* make sure the init_task is aligned to the
* kernel thread size so we can locate the kernel
* stack properly and quickly.
*/
__sdata = .;
. = ALIGN(THREAD_SIZE);
*(.data.init_task)

. = ALIGN(32);
*(.data.cacheline_aligned)

DATA_DATA
*(.data.*)
CONSTRUCTORS

. = ALIGN(THREAD_SIZE);
__edata = .;
}

在VDSP向導生成的LDF文件中，也需要使用數據段，不過它是把代碼和數據混合放在一起的：

sdram
{
INPUT_SECTION_ALIGN(4)
INPUT_SECTIONS($OBJECTS_CORE_A(sdram_bank0) $LIBRARIES_CORE_A(sdram_bank0))

/*$VDSG<insert-input-sections-at-the-start-of-sdram-A> */
/* Text inserted between these $VDSG comments will be preserved */
/*$VDSG<insert-input-sections-at-the-start-of-sdram-A> */

INPUT_SECTIONS($OBJECTS_CORE_A(VDK_ISR_code) $LIBRARIES_CORE_A(VDK_ISR_code))
INPUT_SECTIONS($OBJECTS_CORE_A(program) $LIBRARIES_CORE_A(program))
INPUT_SECTIONS($OBJECTS_CORE_A(noncache_code) $LIBRARIES_CORE_A(noncache_code))
INPUT_SECTIONS($OBJECTS_CORE_A(sdram_data) $LIBRARIES_CORE_A(sdram_data))
INPUT_SECTIONS($OBJECTS_CORE_A(data1) $LIBRARIES_CORE_A(data1))
INPUT_SECTIONS($OBJECTS_CORE_A(voldata) $LIBRARIES_CORE_A(voldata))
INPUT_SECTIONS($OBJECTS_CORE_A(constdata) $LIBRARIES_CORE_A(constdata))

/*$VDSG<insert-input-sections-at-the-end-of-sdram-A>　　 */
/* Text inserted between these $VDSG comments will be preserved */
/*$VDSG<insert-input-sections-at-the-end-of-sdram-A>　　 */

} > MEM_SDRAM

因此我們需要將之拆開分成兩個段：

sdram
{
INPUT_SECTION_ALIGN(4)
INPUT_SECTIONS($OBJECTS_CORE_A(sdram_bank0) $LIBRARIES_CORE_A(sdram_bank0))

/*$VDSG<insert-input-sections-at-the-start-of-sdram-A> */
/* Text inserted between these $VDSG comments will be preserved */
/*$VDSG<insert-input-sections-at-the-start-of-sdram-A> */

INPUT_SECTIONS($OBJECTS_CORE_A(VDK_ISR_code) $LIBRARIES_CORE_A(VDK_ISR_code))
INPUT_SECTIONS($OBJECTS_CORE_A(program) $LIBRARIES_CORE_A(program))
INPUT_SECTIONS($OBJECTS_CORE_A(noncache_code) $LIBRARIES_CORE_A(noncache_code))

/*$VDSG<insert-input-sections-at-the-end-of-sdram-A>　　 */
/* Text inserted between these $VDSG comments will be preserved */
/*$VDSG<insert-input-sections-at-the-end-of-sdram-A>　　 */

} > MEM_SDRAM

.data
{
/* make sure the init_task is aligned to the
* kernel thread size so we can locate the kernel
* stack properly and quickly.
*/
__sdata = .;
INPUT_SECTION_ALIGN(8192)
INPUT_SECTIONS($LIBRARIES_CORE_A(.data.init_task))

INPUT_SECTION_ALIGN(32)
INPUT_SECTIONS($LIBRARIES_CORE_A(.data.cacheline_aligned))

INPUT_SECTIONS($OBJECTS_CORE_A(sdram_data) $LIBRARIES_CORE_A(sdram_data))
INPUT_SECTIONS($OBJECTS_CORE_A(data1) $LIBRARIES_CORE_A(data1))
INPUT_SECTIONS($OBJECTS_CORE_A(voldata) $LIBRARIES_CORE_A(voldata))
INPUT_SECTIONS($OBJECTS_CORE_A(constdata) $LIBRARIES_CORE_A(constdata))
INPUT_SECTIONS($OBJECTS_CORE_A(.data.*))

. = (. + 8191) / 8192 * 8192;
__edata = .;
} > MEM_SDRAM

在這裡直接將THREAD_SIZE替換為8192，避免在LDF中包含頭文件時可能造成的問題。