Linux memory management Initialization

Article Title: linux memory management initialization. Linux is a technology channel of the IT lab in China. Includes basic categories such as desktop applications, Linux system management, kernel research, embedded systems, and open source.

ENTRY (startup_32)

/*

* Set segments to known values.

*/

Cld

Lgdt boot_gdt_descr-_ PAGE_OFFSET/* set the segment register */

Movl $ (_ BOOT_DS), % eax

Movl % eax, % ds

Movl % eax, % es

Movl % eax, % fs

Movl % eax, % gs

/*

* Clear BSS first so that there are no surprises...

* No need to cld as DF is already clear from cld abve...

*/

Xorl % eax, % eax

Movl $ __bss_start-_ PAGE_OFFSET, % edi

Movl $ __bss_stop-_ PAGE_OFFSET, % ecx

Subl % edi, % ecx

Shrl $2, % ecx

Rep; stosl

/*

* Copy bootup parameters out of the way.

* Note: % esi still has the pointer to the real-mode data.

* With the kexec as boot loader, parameter segment might be loaded beyond

* Kernel image and might not even be addressable by early boot page tables.

* (Kexec on panic case). Hence copy out the parameters before initializing

* Page tables.

*/

Movl $ (boot_params-_ PAGE_OFFSET), % edi

Movl $ (PARAM_SIZE/4), % ecx

Cld

Rep

Movsl

Movl boot_params-_ PAGE_OFFSET + NEW_CL_POINTER, % esi

Andl % esi, % esi

Jnz 2f # New command line protocol

Cmpw $ (OLD_CL_MAGIC), OLD_CL_MAGIC_ADDR

Jne 1f

Movzwl OLD_CL_OFFSET, % esi

Addl $ (OLD_CL_BASE_ADDR), % esi

2:

Movl $ (saved_command_line-_ PAGE_OFFSET), % edi

Movl $ (COMMAND_LINE_SIZE/4), % ecx

Rep

Movsl

1:

/*

* Initialize page tables. This creates a PVDF and a set of page

* Tables, which are located immediately beyond _ end. The variable

* Init_pg_tables_end is set up to point to the first "safe" location.

* Mappings are created both at virtual address 0 (identity mapping)

* And PAGE_OFFSET for up to _ end + sizeof (page tables) + INIT_MAP_BEYOND_END.

*

* Warning: don't use % esi or the stack in this code. However, % esp

* Can be used as a GPR if you really need it...

*/

Page_pde_offset = (_ PAGE_OFFSET> 20 );

Movl $ (pg0-_ PAGE_OFFSET), % edi

Movl $ (swapper_pg_dir-_ PAGE_OFFSET), % edx

Movl $0x007, % eax/* 0x007 = PRESENT + RW + USER */

10:

Leal 0x007 (% edi), % ecx/* Create PVDF entry */

Movl % ecx, (% edx)/* Store identity PVDF entry */

Movl % ecx, page_pde_offset (% edx)/* Store kernel PVDF entry */

Addl $4, % edx

Movl $1024, % ecx

11:

Stosl

Addl $0x1000, % eax

Loop 11b

/* End condition: we must map up to and including INIT_MAP_BEYOND_END */

/* Bytes beyond the end of our own page tables; the + 0x007 is the attribute bits */

Leal (INIT_MAP_BEYOND_END + 0x007) (% edi), % ebp

Cmpl % ebp, % eax

Jb 10b

Movl % edi, (init_pg_tables_end-_ PAGE_OFFSET)

# Ifdef CONFIG_SMP

Xorl % ebx, % ebx/* This is the boot CPU (BSP )*/

Jmp 3f

/*

* Non-boot CPU entry point; entered from trampoline. S

* We can't lgdt here, because lgdt itself uses a data segment,

* We know the trampoline has already loaded the boot_gdt_table GDT

* For us.

*/

ENTRY (startup_32_smp)

Cld

Movl $ (_ BOOT_DS), % eax

Movl % eax, % ds

Movl % eax, % es

Movl % eax, % fs

Movl % eax, % gs

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