And another confusing:
In uncompressed code,
================
arch/x86/boot/compressed/head_32.S:
ENTRY(startup_32)
...
testb $(1<<6), BP_loadflags(%esi)
jnz 1f
cli
movl $__BOOT_DS, %eax
movl %eax, %ds
movl %eax, %es
...
===============
Kernel already set these segment resisters.
At 2013-05-02 16:14:23,Jacky <jackyclivia@xxxxxxx> wrote:
Hi, All,
Why kernel reloads these segment registers in startup_32 again ? Just liking the following:
=======================
ENTRY(startup_32)
movl pa(stack_start),%ecx
/* test KEEP_SEGMENTS flag to see if the bootloader is asking
us to not reload segments */
testb $(1<<6), BP_loadflags(%esi)
jnz 2f
/*
* Set segments to known values.
*/
lgdt pa(boot_gdt_descr)
movl $(__BOOT_DS),%eax
movl %eax,%ds
...
======================
Considering bootloader, such as GRUB has already load these segments, so why kernel reloads them again while wasting CPU ?
Thanks,
Jacky
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