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opengnsys_ipxe/src/arch/x86/transitions/librm.S

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/*
* librm: a library for interfacing to real-mode code
*
* Michael Brown <mbrown@fensystems.co.uk>
*
*/
FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL )
/* Drag in local definitions */
#include "librm.h"
/* For switches to/from protected mode */
#define CR0_PE 1
/* Size of various C data structures */
#define SIZEOF_I386_SEG_REGS 12
#define SIZEOF_I386_REGS 32
#define SIZEOF_REAL_MODE_REGS ( SIZEOF_I386_SEG_REGS + SIZEOF_I386_REGS )
#define SIZEOF_I386_FLAGS 4
#define SIZEOF_I386_ALL_REGS ( SIZEOF_REAL_MODE_REGS + SIZEOF_I386_FLAGS )
/* Size of an address */
#ifdef __x86_64__
#define SIZEOF_ADDR 8
#else
#define SIZEOF_ADDR 4
#endif
/* Selectively assemble code for 32-bit/64-bit builds */
#ifdef __x86_64__
#define if32 if 0
#define if64 if 1
#else
#define if32 if 1
#define if64 if 0
#endif
/****************************************************************************
* Global descriptor table
*
* Call init_librm to set up the GDT before attempting to use any
* protected-mode code.
*
* NOTE: This must be located before prot_to_real, otherwise gas
* throws a "can't handle non absolute segment in `ljmp'" error due to
* not knowing the value of REAL_CS when the ljmp is encountered.
*
* Note also that putting ".word gdt_end - gdt - 1" directly into
* gdt_limit, rather than going via gdt_length, will also produce the
* "non absolute segment" error. This is most probably a bug in gas.
****************************************************************************
*/
.section ".data16.gdt", "aw", @progbits
.align 16
gdt:
gdtr: /* The first GDT entry is unused, the GDTR can fit here. */
gdt_limit: .word gdt_length - 1
gdt_base: .long 0
.word 0 /* padding */
.org gdt + VIRTUAL_CS, 0
virtual_cs: /* 32 bit protected mode code segment, virtual addresses */
.word 0xffff, 0
.byte 0, 0x9f, 0xcf, 0
.org gdt + VIRTUAL_DS, 0
virtual_ds: /* 32 bit protected mode data segment, virtual addresses */
.word 0xffff, 0
.byte 0, 0x93, 0xcf, 0
.org gdt + PHYSICAL_CS, 0
physical_cs: /* 32 bit protected mode code segment, physical addresses */
.word 0xffff, 0
.byte 0, 0x9f, 0xcf, 0
.org gdt + PHYSICAL_DS, 0
physical_ds: /* 32 bit protected mode data segment, physical addresses */
.word 0xffff, 0
.byte 0, 0x93, 0xcf, 0
.org gdt + REAL_CS, 0
real_cs: /* 16 bit real mode code segment */
.word 0xffff, 0
.byte 0, 0x9b, 0x00, 0
.org gdt + REAL_DS, 0
real_ds: /* 16 bit real mode data segment */
.word 0xffff, 0
.byte 0, 0x93, 0x00, 0
.org gdt + P2R_DS, 0
p2r_ds: /* 16 bit real mode data segment for prot_to_real transition */
.word 0xffff, ( P2R_DS << 4 )
.byte 0, 0x93, 0x00, 0
gdt_end:
.equ gdt_length, gdt_end - gdt
/****************************************************************************
* Stored real-mode and protected-mode stack pointers
*
* The real-mode stack pointer is stored here whenever real_to_prot
* is called and restored whenever prot_to_real is called. The
* converse happens for the protected-mode stack pointer.
*
* Despite initial appearances this scheme is, in fact re-entrant,
* because program flow dictates that we always return via the point
* we left by. For example:
* PXE API call entry
* 1 real => prot
* ...
* Print a text string
* ...
* 2 prot => real
* INT 10
* 3 real => prot
* ...
* ...
* 4 prot => real
* PXE API call exit
*
* At point 1, the RM mode stack value, say RPXE, is stored in
* rm_ss,sp. We want this value to still be present in rm_ss,sp when
* we reach point 4.
*
* At point 2, the RM stack value is restored from RPXE. At point 3,
* the RM stack value is again stored in rm_ss,sp. This *does*
* overwrite the RPXE that we have stored there, but it's the same
* value, since the code between points 2 and 3 has managed to return
* to us.
****************************************************************************
*/
.section ".bss.rm_sp", "aw", @nobits
.globl rm_sp
rm_sp: .word 0
.section ".bss.rm_ss", "aw", @nobits
.globl rm_ss
rm_ss: .word 0
.section ".data.pm_esp", "aw", @progbits
pm_esp: .long VIRTUAL(_estack)
/****************************************************************************
* Virtual address offsets
*
* These are used by the protected-mode code to map between virtual
* and physical addresses, and to access variables in the .text16 or
* .data16 segments.
****************************************************************************
*/
.struct 0
VA_VIRT_OFFSET: .space SIZEOF_ADDR
VA_TEXT16: .space SIZEOF_ADDR
VA_DATA16: .space SIZEOF_ADDR
VA_SIZE:
.previous
/* Internal copies, used only by librm itself */
.section ".bss16.rm_virt_addrs", "aw", @nobits
rm_virt_addrs: .space VA_SIZE
.equ rm_virt_offset, ( rm_virt_addrs + VA_VIRT_OFFSET )
.equ rm_text16, ( rm_virt_addrs + VA_TEXT16 )
.equ rm_data16, ( rm_virt_addrs + VA_DATA16 )
/* Externally visible variables, used by C code */
.section ".bss.virt_addrs", "aw", @nobits
virt_addrs: .space VA_SIZE
.globl virt_offset
.equ virt_offset, ( virt_addrs + VA_VIRT_OFFSET )
.globl text16
.equ text16, ( virt_addrs + VA_TEXT16 )
.globl data16
.equ data16, ( virt_addrs + VA_DATA16 )
/****************************************************************************
* init_librm (real-mode far call, 16-bit real-mode far return address)
*
* Initialise the GDT ready for transitions to protected mode.
*
* Parameters:
* %cs : .text16 segment
* %ds : .data16 segment
* %edi : Physical base of protected-mode code
****************************************************************************
*/
.section ".text16.init_librm", "ax", @progbits
.code16
.globl init_librm
init_librm:
/* Preserve registers */
pushl %eax
pushl %ebx
pushl %edi
/* Store rm_virt_offset and set up virtual_cs and virtual_ds segments */
subl $VIRTUAL(_textdata), %edi
movl %edi, rm_virt_offset
.if64 ; setae (rm_virt_offset+4) ; .endif
movl %edi, %eax
movw $virtual_cs, %bx
call set_seg_base
movw $virtual_ds, %bx
call set_seg_base
/* Store rm_cs and rm_text16, set up real_cs segment */
xorl %eax, %eax
movw %cs, %ax
movw %ax, %cs:rm_cs
shll $4, %eax
movw $real_cs, %bx
call set_seg_base
.if32 ; subl %edi, %eax ; .endif
movl %eax, rm_text16
/* Store rm_ds and rm_data16, set up real_ds segment and GDT base */
xorl %eax, %eax
movw %ds, %ax
movw %ax, %cs:rm_ds
shll $4, %eax
movw $real_ds, %bx
call set_seg_base
movl %eax, gdt_base
addl $gdt, gdt_base
.if32 ; subl %edi, %eax ; .endif
movl %eax, rm_data16
/* Switch to protected mode */
virtcall init_librm_pmode
.section ".text.init_librm", "ax", @progbits
.code32
init_librm_pmode:
/* Store virt_offset, text16, and data16 */
pushw %ds
movw $REAL_DS, %ax
movw %ax, %ds
movl $rm_virt_addrs, %esi
movl $VIRTUAL(virt_addrs), %edi
movl $( VA_SIZE / 4 ), %ecx
rep movsl
popw %ds
/* Return to real mode */
ret
.section ".text16.init_librm", "ax", @progbits
.code16
init_librm_rmode:
/* Initialise IDT */
virtcall init_idt
/* Restore registers */
popl %edi
popl %ebx
popl %eax
lret
.section ".text16.set_seg_base", "ax", @progbits
.code16
set_seg_base:
1: movw %ax, 2(%bx)
rorl $16, %eax
movb %al, 4(%bx)
movb %ah, 7(%bx)
roll $16, %eax
ret
/****************************************************************************
* real_to_prot (real-mode near call, 32-bit virtual return address)
*
* Switch from 16-bit real-mode to 32-bit protected mode with virtual
* addresses. The real-mode %ss:sp is stored in rm_ss and rm_sp, and
* the protected-mode %esp is restored from the saved pm_esp.
* Interrupts are disabled. All other registers may be destroyed.
*
* The return address for this function should be a 32-bit virtual
* address.
*
* Parameters:
* %ecx : number of bytes to move from RM stack to PM stack
*
****************************************************************************
*/
.section ".text16.real_to_prot", "ax", @progbits
.code16
real_to_prot:
/* Enable A20 line */
call enable_a20
/* A failure at this point is fatal, and there's nothing we
* can do about it other than lock the machine to make the
* problem immediately visible.
*/
1: jc 1b
/* Make sure we have our data segment available */
movw %cs:rm_ds, %ds
/* Add protected-mode return address to length of data to be copied */
addw $4, %cx /* %ecx must be less than 64kB anyway */
/* Real-mode %ss:%sp => %ebp:%edx and virtual address => %esi */
xorl %ebp, %ebp
movw %ss, %bp
movzwl %sp, %edx
movl %ebp, %eax
shll $4, %eax
addr32 leal (%eax,%edx), %esi
subl rm_virt_offset, %esi
/* Load protected-mode global descriptor table */
data32 lgdt gdtr
/* Zero segment registers. This wastes around 12 cycles on
* real hardware, but saves a substantial number of emulated
* instructions under KVM.
*/
xorw %ax, %ax
movw %ax, %ds
movw %ax, %es
movw %ax, %fs
movw %ax, %gs
movw %ax, %ss
/* Switch to protected mode */
cli
movl %cr0, %eax
orb $CR0_PE, %al
movl %eax, %cr0
data32 ljmp $VIRTUAL_CS, $VIRTUAL(r2p_pmode)
.section ".text.real_to_prot", "ax", @progbits
.code32
r2p_pmode:
/* Set up protected-mode data segments and stack pointer */
movw $VIRTUAL_DS, %ax
movw %ax, %ds
movw %ax, %es
movw %ax, %fs
movw %ax, %gs
movw %ax, %ss
movl VIRTUAL(pm_esp), %esp
/* Load protected-mode interrupt descriptor table */
lidt VIRTUAL(idtr)
/* Record real-mode %ss:sp (after removal of data) */
movw %bp, VIRTUAL(rm_ss)
addl %ecx, %edx
movw %dx, VIRTUAL(rm_sp)
/* Move data from RM stack to PM stack */
subl %ecx, %esp
movl %esp, %edi
rep movsb
/* Return to virtual address */
ret
/****************************************************************************
* prot_to_real (protected-mode near call, 32-bit real-mode return address)
*
* Switch from 32-bit protected mode with virtual addresses to 16-bit
* real mode. The protected-mode %esp is stored in pm_esp and the
* real-mode %ss:sp is restored from the saved rm_ss and rm_sp. The
* high word of the real-mode %esp is set to zero. All real-mode data
* segment registers are loaded from the saved rm_ds. Interrupts are
* *not* enabled, since we want to be able to use prot_to_real in an
* ISR. All other registers may be destroyed.
*
* The return address for this function should be a 32-bit (sic)
* real-mode offset within .code16.
*
* Parameters:
* %ecx : number of bytes to move from PM stack to RM stack
* %esi : real-mode global and interrupt descriptor table registers
*
****************************************************************************
*/
.section ".text.prot_to_real", "ax", @progbits
.code32
prot_to_real:
/* Copy real-mode global descriptor table register to RM code segment */
movl VIRTUAL(text16), %edi
.if64 ; subl VIRTUAL(virt_offset), %edi ; .endif
leal rm_gdtr(%edi), %edi
movsw
movsl
/* Load real-mode interrupt descriptor table register */
lidt (%esi)
/* Add return address to data to be moved to RM stack */
addl $4, %ecx
/* Real-mode %ss:sp => %ebp:edx and virtual address => %edi */
movzwl VIRTUAL(rm_ss), %ebp
movzwl VIRTUAL(rm_sp), %edx
subl %ecx, %edx
movl %ebp, %eax
shll $4, %eax
leal (%eax,%edx), %edi
subl VIRTUAL(virt_offset), %edi
/* Move data from PM stack to RM stack */
movl %esp, %esi
rep movsb
/* Record protected-mode %esp (after removal of data) */
movl %esi, VIRTUAL(pm_esp)
/* Load real-mode segment limits */
movw $P2R_DS, %ax
movw %ax, %ds
movw %ax, %es
movw %ax, %fs
movw %ax, %gs
movw %ax, %ss
ljmp $REAL_CS, $p2r_rmode
.section ".text16.prot_to_real", "ax", @progbits
.code16
p2r_rmode:
/* Load real-mode GDT */
data32 lgdt %cs:rm_gdtr
/* Switch to real mode */
movl %cr0, %eax
andb $0!CR0_PE, %al
movl %eax, %cr0
p2r_ljmp_rm_cs:
ljmp $0, $1f
1:
/* Set up real-mode data segments and stack pointer */
movw %cs:rm_ds, %ax
movw %ax, %ds
movw %ax, %es
movw %ax, %fs
movw %ax, %gs
movw %bp, %ss
movl %edx, %esp
/* Return to real-mode address */
data32 ret
/* Real-mode code and data segments. Assigned by the call to
* init_librm. rm_cs doubles as the segment part of the jump
* instruction used by prot_to_real. Both are located in
* .text16 rather than .data16: rm_cs since it forms part of
* the jump instruction within the code segment, and rm_ds
* since real-mode code needs to be able to locate the data
* segment with no other reference available.
*/
.globl rm_cs
.equ rm_cs, ( p2r_ljmp_rm_cs + 3 )
.section ".text16.data.rm_ds", "aw", @progbits
.globl rm_ds
rm_ds: .word 0
/* Real-mode global and interrupt descriptor table registers */
.section ".text16.data.rm_gdtr", "aw", @progbits
rm_gdtr:
.word 0 /* Limit */
.long 0 /* Base */
/****************************************************************************
* prot_call (real-mode near call, 16-bit real-mode near return address)
*
* Call a specific C function in the protected-mode code. The
* prototype of the C function must be
* void function ( struct i386_all_regs *ix86 );
* ix86 will point to a struct containing the real-mode registers
* at entry to prot_call.
*
* All registers will be preserved across prot_call(), unless the C
* function explicitly overwrites values in ix86. Interrupt status
* and GDT will also be preserved. Gate A20 will be enabled.
*
* Note that prot_call() does not rely on the real-mode stack
* remaining intact in order to return, since everything relevant is
* copied to the protected-mode stack for the duration of the call.
* In particular, this means that a real-mode prefix can make a call
* to main() which will return correctly even if the prefix's stack
* gets vapourised during the Etherboot run. (The prefix cannot rely
* on anything else on the stack being preserved, so should move any
* critical data to registers before calling main()).
*
* Parameters:
* function : virtual address of protected-mode function to call
*
* Example usage:
* pushl $pxe_api_call
* call prot_call
* to call in to the C function
* void pxe_api_call ( struct i386_all_regs *ix86 );
****************************************************************************
*/
.struct 0
PC_OFFSET_GDT: .space 6
PC_OFFSET_IDT: .space 6
PC_OFFSET_IX86: .space SIZEOF_I386_ALL_REGS
PC_OFFSET_PADDING: .space 2 /* for alignment */
PC_OFFSET_RETADDR: .space 2
PC_OFFSET_FUNCTION: .space 4
PC_OFFSET_END:
.previous
.section ".text16.prot_call", "ax", @progbits
.code16
.globl prot_call
prot_call:
/* Preserve registers, flags and GDT on external RM stack */
pushfw /* padding */
pushfl
pushal
pushw %gs
pushw %fs
pushw %es
pushw %ds
pushw %ss
pushw %cs
subw $PC_OFFSET_IX86, %sp
movw %sp, %bp
sidt PC_OFFSET_IDT(%bp)
sgdt PC_OFFSET_GDT(%bp)
/* For sanity's sake, clear the direction flag as soon as possible */
cld
/* Switch to protected mode and move register dump to PM stack */
movl $PC_OFFSET_END, %ecx
pushl $VIRTUAL(pc_pmode)
jmp real_to_prot
.section ".text.prot_call", "ax", @progbits
.code32
pc_pmode:
/* Call function */
leal PC_OFFSET_IX86(%esp), %eax
pushl %eax
call *(PC_OFFSET_FUNCTION+4)(%esp)
popl %eax /* discard */
/* Switch to real mode and move register dump back to RM stack */
movl $PC_OFFSET_END, %ecx
movl %esp, %esi
pushl $pc_rmode
jmp prot_to_real
.section ".text16.prot_call", "ax", @progbits
.code16
pc_rmode:
/* Restore registers and flags and return */
addw $( PC_OFFSET_IX86 + 4 /* also skip %cs and %ss */ ), %sp
popw %ds
popw %es
popw %fs
popw %gs
popal
/* popal skips %esp. We therefore want to do "movl -20(%sp),
* %esp", but -20(%sp) is not a valid 80386 expression.
* Fortunately, prot_to_real() zeroes the high word of %esp, so
* we can just use -20(%esp) instead.
*/
addr32 movl -20(%esp), %esp
popfl
popfw /* padding */
ret $4
/****************************************************************************
* real_call (protected-mode near call, 32-bit virtual return address)
*
* Call a real-mode function from protected-mode code.
*
* The non-segment register values will be passed directly to the
* real-mode code. The segment registers will be set as per
* prot_to_real. The non-segment register values set by the real-mode
* function will be passed back to the protected-mode caller. A
* result of this is that this routine cannot be called directly from
* C code, since it clobbers registers that the C ABI expects the
* callee to preserve.
*
* librm.h defines a convenient macro REAL_CODE() for using real_call.
* See librm.h and realmode.h for details and examples.
*
* Parameters:
* (32-bit) near pointer to real-mode function to call
*
* Returns: none
****************************************************************************
*/
.struct 0
RC_OFFSET_REGS: .space SIZEOF_I386_REGS
RC_OFFSET_REGS_END:
RC_OFFSET_RETADDR: .space 4
RC_OFFSET_FUNCTION: .space 4
RC_OFFSET_END:
.previous
.section ".text.real_call", "ax", @progbits
.code32
.globl real_call
real_call:
/* Create register dump and function pointer copy on PM stack */
pushal
pushl RC_OFFSET_FUNCTION(%esp)
/* Switch to real mode and move register dump to RM stack */
movl $( RC_OFFSET_REGS_END + 4 /* function pointer copy */ ), %ecx
pushl $rc_rmode
movl $VIRTUAL(rm_default_gdtr_idtr), %esi
jmp prot_to_real
.section ".text16.real_call", "ax", @progbits
.code16
rc_rmode:
/* Call real-mode function */
popl rc_function
popal
call *rc_function
pushal
/* For sanity's sake, clear the direction flag as soon as possible */
cld
/* Switch to protected mode and move register dump back to PM stack */
movl $RC_OFFSET_REGS_END, %ecx
pushl $VIRTUAL(rc_pmode)
jmp real_to_prot
.section ".text.real_call", "ax", @progbits
.code32
rc_pmode:
/* Restore registers and return */
popal
ret $4
/* Function vector, used because "call xx(%sp)" is not a valid
* 16-bit expression.
*/
.section ".bss16.rc_function", "aw", @nobits
rc_function: .word 0, 0
/* Default real-mode global and interrupt descriptor table registers */
.section ".data.rm_default_gdtr_idtr", "aw", @progbits
rm_default_gdtr_idtr:
.word 0 /* Global descriptor table limit */
.long 0 /* Global descriptor table base */
.word 0x03ff /* Interrupt descriptor table limit */
.long 0 /* Interrupt descriptor table base */
/****************************************************************************
* flatten_real_mode (real-mode near call)
*
* Switch to flat real mode
*
****************************************************************************
*/
.section ".text16.flatten_real_mode", "ax", @progbits
.code16
.globl flatten_real_mode
flatten_real_mode:
/* Modify GDT to use flat real mode */
movb $0x8f, real_cs + 6
movb $0x8f, real_ds + 6
/* Call dummy protected-mode function */
virtcall flatten_dummy
/* Restore GDT */
movb $0x00, real_cs + 6
movb $0x00, real_ds + 6
/* Return */
ret
.section ".text.flatten_dummy", "ax", @progbits
.code32
flatten_dummy:
ret
/****************************************************************************
* Interrupt wrapper
*
* Used by the protected-mode interrupt vectors to call the
* interrupt() function.
*
* May be entered with either physical or virtual stack segment.
****************************************************************************
*/
.section ".text.interrupt_wrapper", "ax", @progbits
.code32
.globl interrupt_wrapper
interrupt_wrapper:
/* Preserve segment registers and original %esp */
pushl %ds
pushl %es
pushl %fs
pushl %gs
pushl %ss
pushl %esp
/* Switch to virtual addressing */
call _intr_to_virt
/* Expand IRQ number to whole %eax register */
movzbl %al, %eax
/* Call interrupt handler */
call interrupt
/* Restore original stack and segment registers */
lss (%esp), %esp
popl %ss
popl %gs
popl %fs
popl %es
popl %ds
/* Restore registers and return */
popal
iret
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