[librm] Transition to protected mode within init_librm()
Long-mode operation will require page tables, which are too large to sensibly fit in our .data16 segment in base memory. Add a portion of init_librm() running in 32-bit protected mode to provide access to high memory. Use this portion of init_librm() to initialise the .textdata variables "virt_offset", "text16", and "data16", eliminating the redundant (re)initialisation currently performed on every mode transition as part of real_to_prot(). Signed-off-by: Michael Brown <mcb30@ipxe.org>
This commit is contained in:
Michael Brown
parent
31b5c2e753
commit
6eb1c927a3
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@ -14,10 +14,7 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
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#define PHYSICAL_DS 0x20
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#define REAL_CS 0x28
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#define REAL_DS 0x30
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#if 0
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#define LONG_CS 0x38
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#define LONG_DS 0x40
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#endif
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#define P2R_DS 0x38
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#ifdef ASSEMBLY
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@ -70,14 +70,96 @@ real_cs: /* 16 bit real mode code segment */
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.word 0xffff, 0
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.byte 0, 0x9b, 0x00, 0
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.org gdt + REAL_DS
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.org gdt + REAL_DS, 0
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real_ds: /* 16 bit real mode data segment */
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.word 0xffff, ( REAL_DS << 4 )
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.word 0xffff, 0
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.byte 0, 0x93, 0x00, 0
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.org gdt + P2R_DS, 0
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p2r_ds: /* 16 bit real mode data segment for prot_to_real transition */
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.word 0xffff, ( P2R_DS << 4 )
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.byte 0, 0x93, 0x00, 0
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gdt_end:
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.equ gdt_length, gdt_end - gdt
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/****************************************************************************
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* Stored real-mode and protected-mode stack pointers
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*
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* The real-mode stack pointer is stored here whenever real_to_prot
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* is called and restored whenever prot_to_real is called. The
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* converse happens for the protected-mode stack pointer.
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*
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* Despite initial appearances this scheme is, in fact re-entrant,
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* because program flow dictates that we always return via the point
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* we left by. For example:
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* PXE API call entry
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* 1 real => prot
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* ...
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* Print a text string
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* ...
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* 2 prot => real
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* INT 10
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* 3 real => prot
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* ...
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* ...
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* 4 prot => real
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* PXE API call exit
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*
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* At point 1, the RM mode stack value, say RPXE, is stored in
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* rm_ss,sp. We want this value to still be present in rm_ss,sp when
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* we reach point 4.
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*
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* At point 2, the RM stack value is restored from RPXE. At point 3,
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* the RM stack value is again stored in rm_ss,sp. This *does*
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* overwrite the RPXE that we have stored there, but it's the same
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* value, since the code between points 2 and 3 has managed to return
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* to us.
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****************************************************************************
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*/
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.section ".bss.rm_sp", "aw", @nobits
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.globl rm_sp
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rm_sp: .word 0
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.section ".bss.rm_ss", "aw", @nobits
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.globl rm_ss
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rm_ss: .word 0
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.section ".data.pm_esp", "aw", @progbits
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pm_esp: .long _estack
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/****************************************************************************
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* Virtual address offsets
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*
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* These are used by the protected-mode code to map between virtual
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* and physical addresses, and to access variables in the .text16 or
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* .data16 segments.
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****************************************************************************
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*/
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.struct 0
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VA_VIRT_OFFSET: .space 4
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VA_TEXT16: .space 4
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VA_DATA16: .space 4
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VA_SIZE:
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.previous
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/* Internal copies, used only by librm itself */
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.section ".bss16.rm_virt_addrs", "aw", @nobits
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rm_virt_addrs: .space VA_SIZE
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.equ rm_virt_offset, ( rm_virt_addrs + VA_VIRT_OFFSET )
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.equ rm_text16, ( rm_virt_addrs + VA_TEXT16 )
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.equ rm_data16, ( rm_virt_addrs + VA_DATA16 )
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/* Externally visible variables, used by C code */
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.section ".bss.virt_addrs", "aw", @nobits
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virt_addrs: .space VA_SIZE
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.globl virt_offset
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.equ virt_offset, ( virt_addrs + VA_VIRT_OFFSET )
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.globl text16
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.equ text16, ( virt_addrs + VA_TEXT16 )
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.globl data16
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.equ data16, ( virt_addrs + VA_DATA16 )
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/****************************************************************************
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* init_librm (real-mode far call, 16-bit real-mode far return address)
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*
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@ -96,45 +178,65 @@ init_librm:
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/* Preserve registers */
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pushl %eax
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pushl %ebx
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pushl %edi
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/* Store virt_offset and set up virtual_cs and virtual_ds segments */
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/* Store rm_virt_offset and set up virtual_cs and virtual_ds segments */
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movl %edi, rm_virt_offset
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movl %edi, %eax
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movw $virtual_cs, %bx
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call set_seg_base
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movw $virtual_ds, %bx
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call set_seg_base
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movl %edi, rm_virt_offset
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call set_seg_base
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/* Negate virt_offset */
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negl %edi
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/* Store rm_cs and text16, set up real_cs segment */
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/* Store rm_cs and rm_text16, set up real_cs segment */
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xorl %eax, %eax
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movw %cs, %ax
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movw %ax, %cs:rm_cs
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shll $4, %eax
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movw $real_cs, %bx
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call set_seg_base
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addr32 leal (%eax, %edi), %ebx
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movl %ebx, rm_text16
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subl %edi, %eax
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movl %eax, rm_text16
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/* Store rm_ds and data16 */
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/* Store rm_ds and rm_data16, set up real_ds segment and GDT base */
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xorl %eax, %eax
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movw %ds, %ax
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movw %ax, %cs:rm_ds
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shll $4, %eax
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addr32 leal (%eax, %edi), %ebx
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movl %ebx, rm_data16
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/* Set GDT base */
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movw $real_ds, %bx
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call set_seg_base
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movl %eax, gdt_base
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addl $gdt, gdt_base
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subl %edi, %eax
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movl %eax, rm_data16
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/* Switch to protected mode */
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virtcall init_librm_pmode
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.section ".text.init_librm", "ax", @progbits
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.code32
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init_librm_pmode:
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/* Store virt_offset, text16, and data16 */
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pushw %ds
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movw $REAL_DS, %ax
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movw %ax, %ds
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movl $rm_virt_addrs, %esi
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movl $virt_addrs, %edi
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movl $( VA_SIZE / 4 ), %ecx
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rep movsl
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popw %ds
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/* Return to real mode */
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ret
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.section ".text16.init_librm", "ax", @progbits
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.code16
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init_librm_rmode:
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/* Initialise IDT */
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virtcall init_idt
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/* Restore registers */
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negl %edi
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popl %edi
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popl %ebx
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popl %eax
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lret
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@ -177,16 +279,10 @@ real_to_prot:
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1: jc 1b
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/* Make sure we have our data segment available */
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movw %cs:rm_ds, %ax
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movw %ax, %ds
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movw %cs:rm_ds, %ds
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/* Add virt_offset, text16 and data16 to stack to be
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* copied, and also copy the return address.
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*/
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pushl rm_virt_offset
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pushl rm_text16
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pushl rm_data16
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addw $16, %cx /* %ecx must be less than 64kB anyway */
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/* Add protected-mode return address to length of data to be copied */
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addw $4, %cx /* %ecx must be less than 64kB anyway */
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/* Real-mode %ss:%sp => %ebp:%edx and virtual address => %esi */
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xorl %ebp, %ebp
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@ -242,11 +338,6 @@ r2p_pmode:
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movl %esp, %edi
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rep movsb
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/* Publish virt_offset, text16 and data16 for PM code to use */
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popl data16
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popl text16
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popl virt_offset
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/* Return to virtual address */
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ret
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@ -284,7 +375,7 @@ prot_to_real:
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/* Add return address to data to be moved to RM stack */
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addl $4, %ecx
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/* Real-mode %ss:sp => %ebp:edx and virtual address => %edi */
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movzwl rm_ss, %ebp
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movzwl rm_sp, %edx
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@ -293,16 +384,16 @@ prot_to_real:
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shll $4, %eax
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leal (%eax,%edx), %edi
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subl virt_offset, %edi
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/* Move data from PM stack to RM stack */
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movl %esp, %esi
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rep movsb
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/* Record protected-mode %esp (after removal of data) */
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movl %esi, pm_esp
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/* Load real-mode segment limits */
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movw $REAL_DS, %ax
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movw $P2R_DS, %ax
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movw %ax, %ds
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movw %ax, %es
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movw %ax, %fs
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@ -604,71 +695,3 @@ interrupt_wrapper:
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/* Restore registers and return */
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popal
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iret
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/****************************************************************************
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* Stored real-mode and protected-mode stack pointers
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*
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* The real-mode stack pointer is stored here whenever real_to_prot
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* is called and restored whenever prot_to_real is called. The
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* converse happens for the protected-mode stack pointer.
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*
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* Despite initial appearances this scheme is, in fact re-entrant,
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* because program flow dictates that we always return via the point
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* we left by. For example:
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* PXE API call entry
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* 1 real => prot
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* ...
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* Print a text string
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* ...
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* 2 prot => real
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* INT 10
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* 3 real => prot
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* ...
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* ...
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* 4 prot => real
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* PXE API call exit
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*
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* At point 1, the RM mode stack value, say RPXE, is stored in
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* rm_ss,sp. We want this value to still be present in rm_ss,sp when
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* we reach point 4.
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*
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* At point 2, the RM stack value is restored from RPXE. At point 3,
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* the RM stack value is again stored in rm_ss,sp. This *does*
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* overwrite the RPXE that we have stored there, but it's the same
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* value, since the code between points 2 and 3 has managed to return
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* to us.
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****************************************************************************
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*/
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.section ".bss.rm_sp", "aw", @nobits
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.globl rm_sp
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rm_sp: .word 0
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.section ".bss.rm_ss", "aw", @nobits
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.globl rm_ss
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rm_ss: .word 0
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.section ".data.pm_esp", "aw", @progbits
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pm_esp: .long _estack
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/****************************************************************************
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* Virtual address offsets
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*
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* These are used by the protected-mode code to map between virtual
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* and physical addresses, and to access variables in the .text16 or
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* .data16 segments.
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****************************************************************************
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*/
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/* Internal copies, created by init_librm (which runs in real mode) */
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.section ".bss16.rm_virt_offset", "aw", @nobits
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rm_virt_offset: .long 0
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rm_text16: .long 0
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rm_data16: .long 0
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/* Externally-visible copies, created by real_to_prot */
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.section ".bss.virt_offset", "aw", @nobits
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.globl virt_offset
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virt_offset: .long 0
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.globl text16
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text16: .long 0
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.globl data16
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data16: .long 0
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