diff options
Diffstat (limited to 'contrib/syslinux-4.02/gpxe/src/arch/i386/transitions/librm.S')
| -rw-r--r-- | contrib/syslinux-4.02/gpxe/src/arch/i386/transitions/librm.S | 581 |
1 files changed, 581 insertions, 0 deletions
diff --git a/contrib/syslinux-4.02/gpxe/src/arch/i386/transitions/librm.S b/contrib/syslinux-4.02/gpxe/src/arch/i386/transitions/librm.S new file mode 100644 index 0000000..cb27ef3 --- /dev/null +++ b/contrib/syslinux-4.02/gpxe/src/arch/i386/transitions/librm.S @@ -0,0 +1,581 @@ +/* + * librm: a library for interfacing to real-mode code + * + * Michael Brown <mbrown@fensystems.co.uk> + * + */ + +FILE_LICENCE ( GPL2_OR_LATER ) + +/* 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 ) + + .arch i386 + +/**************************************************************************** + * Global descriptor table + * + * Call init_librm to set up the GDT before attempting to use any + * protected-mode code. + * + * Define FLATTEN_REAL_MODE if you want to use so-called "flat real + * mode" with 4GB limits instead. + * + * 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. + **************************************************************************** + */ + +#ifdef FLATTEN_REAL_MODE +#define RM_LIMIT_16_19__AVL__SIZE__GRANULARITY 0x8f +#else +#define RM_LIMIT_16_19__AVL__SIZE__GRANULARITY 0x00 +#endif + .section ".data16", "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, RM_LIMIT_16_19__AVL__SIZE__GRANULARITY, 0 + + .org gdt + REAL_DS +real_ds: /* 16 bit real mode data segment */ + .word 0xffff, 0 + .byte 0, 0x93, RM_LIMIT_16_19__AVL__SIZE__GRANULARITY, 0 + +gdt_end: + .equ gdt_length, gdt_end - gdt + +/**************************************************************************** + * 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 (virt_offset) + **************************************************************************** + */ + .section ".text16", "ax", @progbits + .code16 + .globl init_librm +init_librm: + /* Preserve registers */ + pushl %eax + pushl %ebx + + /* Store _virt_offset and set up virtual_cs and virtual_ds segments */ + movl %edi, %eax + movw $virtual_cs, %bx + call set_seg_base + movw $virtual_ds, %bx + call set_seg_base + movl %edi, _virt_offset + + /* Negate virt_offset */ + negl %edi + + /* Store rm_cs and _text16, set up real_cs segment */ + xorl %eax, %eax + movw %cs, %ax + movw %ax, rm_cs + shll $4, %eax + movw $real_cs, %bx + call set_seg_base + addr32 leal (%eax, %edi), %ebx + movl %ebx, _text16 + + /* Store rm_ds and _data16, set up real_ds segment */ + xorl %eax, %eax + movw %ds, %ax + movw %ax, %cs:rm_ds + shll $4, %eax + movw $real_ds, %bx + call set_seg_base + addr32 leal (%eax, %edi), %ebx + movl %ebx, _data16 + + /* Set GDT and IDT base */ + movl %eax, gdt_base + addl $gdt, gdt_base + call idt_init + + /* Restore registers */ + negl %edi + popl %ebx + popl %eax + lret + + .section ".text16", "ax", @progbits + .code16 + .weak idt_init +set_seg_base: +1: movw %ax, 2(%bx) + rorl $16, %eax + movb %al, 4(%bx) + movb %ah, 7(%bx) + roll $16, %eax +idt_init: /* Reuse the return opcode here */ + 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", "ax", @progbits + .code16 +real_to_prot: + /* Make sure we have our data segment available */ + movw %cs:rm_ds, %ax + movw %ax, %ds + + /* Add _virt_offset, _text16 and _data16 to stack to be + * copied, and also copy the return address. + */ + pushl _virt_offset + pushl _text16 + pushl _data16 + addw $16, %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 _virt_offset, %esi + + /* Switch to protected mode */ + cli + data32 lgdt gdtr + data32 lidt idtr + movl %cr0, %eax + orb $CR0_PE, %al + movl %eax, %cr0 + data32 ljmp $VIRTUAL_CS, $1f + .section ".text", "ax", @progbits + .code32 +1: + /* 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 pm_esp, %esp + + /* Record real-mode %ss:sp (after removal of data) */ + movw %bp, rm_ss + addl %ecx, %edx + movw %dx, rm_sp + + /* Move data from RM stack to PM stack */ + subl %ecx, %esp + movl %esp, %edi + rep movsb + + /* Publish virt_offset, text16 and data16 for PM code to use */ + popl data16 + popl text16 + popl virt_offset + + /* Return to virtual address */ + ret + + /* Default IDTR with no interrupts */ + .section ".data16", "aw", @progbits + .weak idtr +idtr: +rm_idtr: + .word 0xffff /* limit */ + .long 0 /* base */ + +/**************************************************************************** + * 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 + * + **************************************************************************** + */ + .section ".text", "ax", @progbits + .code32 +prot_to_real: + /* 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 rm_ss, %ebp + movzwl rm_sp, %edx + subl %ecx, %edx + movl %ebp, %eax + shll $4, %eax + leal (%eax,%edx), %edi + subl 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, pm_esp + + /* Load real-mode segment limits */ + movw $REAL_DS, %ax + movw %ax, %ds + movw %ax, %es + movw %ax, %fs + movw %ax, %gs + movw %ax, %ss + ljmp $REAL_CS, $1f + .section ".text16", "ax", @progbits + .code16 +1: + /* Switch to real mode */ + movl %cr0, %eax + andb $0!CR0_PE, %al + movl %eax, %cr0 + ljmp *p2r_jump_vector +p2r_jump_target: + + /* 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 + + /* Reset IDTR to the real-mode defaults */ + data32 lidt rm_idtr + + /* 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 + * vector used by prot_to_real. rm_ds is located in .text16 + * rather than .data16 because code needs to be able to locate + * the data segment. + */ + .section ".data16", "aw", @progbits +p2r_jump_vector: + .word p2r_jump_target + .globl rm_cs +rm_cs: .word 0 + .globl rm_ds + .section ".text16.data", "aw", @progbits +rm_ds: .word 0 + +/**************************************************************************** + * prot_call (real-mode far call, 16-bit real-mode far 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 + * addw $4, %sp + * to call in to the C function + * void pxe_api_call ( struct i386_all_regs *ix86 ); + **************************************************************************** + */ + +#define PC_OFFSET_GDT ( 0 ) +#define PC_OFFSET_IDT ( PC_OFFSET_GDT + 8 /* pad to 8 to keep alignment */ ) +#define PC_OFFSET_IX86 ( PC_OFFSET_IDT + 8 /* pad to 8 to keep alignment */ ) +#define PC_OFFSET_RETADDR ( PC_OFFSET_IX86 + SIZEOF_I386_ALL_REGS ) +#define PC_OFFSET_FUNCTION ( PC_OFFSET_RETADDR + 4 ) +#define PC_OFFSET_END ( PC_OFFSET_FUNCTION + 4 ) + + .section ".text16", "ax", @progbits + .code16 + .globl prot_call +prot_call: + /* Preserve registers, flags and GDT on external RM stack */ + pushfl + pushal + pushw %gs + pushw %fs + pushw %es + pushw %ds + pushw %ss + pushw %cs + subw $16, %sp + movw %sp, %bp + sidt 8(%bp) + sgdt (%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 $1f + jmp real_to_prot + .section ".text", "ax", @progbits + .code32 +1: + /* Set up environment expected by C code */ + call gateA20_set + + /* 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 + pushl $1f + jmp prot_to_real + .section ".text16", "ax", @progbits + .code16 +1: + /* Reload GDT and IDT, restore registers and flags and return */ + movw %sp, %bp + data32 lgdt (%bp) + data32 lidt 8(%bp) + addw $20, %sp /* also skip %cs and %ss */ + 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 + lret + +/**************************************************************************** + * 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. Gate A20 will *not* be automatically + * re-enabled. Since we always run from an even megabyte of memory, + * we are guaranteed to return successfully to the protected-mode + * code, which should then call gateA20_set() if it suspects that gate + * A20 may have been disabled. Note that enabling gate A20 is a + * potentially slow operation that may also cause keyboard input to be + * lost; this is why it is not done automatically. + * + * 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 + **************************************************************************** + */ + +#define RC_OFFSET_PRESERVE_REGS ( 0 ) +#define RC_OFFSET_RETADDR ( RC_OFFSET_PRESERVE_REGS + SIZEOF_I386_REGS ) +#define RC_OFFSET_FUNCTION ( RC_OFFSET_RETADDR + 4 ) +#define RC_OFFSET_END ( RC_OFFSET_FUNCTION + 4 ) + + .section ".text", "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_RETADDR + 4 /* function pointer copy */ ), %ecx + pushl $1f + jmp prot_to_real + .section ".text16", "ax", @progbits + .code16 +1: + /* 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_RETADDR, %ecx + pushl $1f + jmp real_to_prot + .section ".text", "ax", @progbits + .code32 +1: + /* Restore registers and return */ + popal + ret + + + /* Function vector, used because "call xx(%sp)" is not a valid + * 16-bit expression. + */ + .section ".data16", "aw", @progbits +rc_function: .word 0, 0 + +/**************************************************************************** + * 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 ".data", "aw", @progbits + .globl rm_sp +rm_sp: .word 0 + .globl rm_ss +rm_ss: .word 0 +pm_esp: .long _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. + **************************************************************************** + */ + /* Internal copies, created by init_librm (which runs in real mode) */ + .section ".data16", "aw", @progbits +_virt_offset: .long 0 +_text16: .long 0 +_data16: .long 0 + + /* Externally-visible copies, created by real_to_prot */ + .section ".data", "aw", @progbits + .globl virt_offset +virt_offset: .long 0 + .globl text16 +text16: .long 0 + .globl data16 +data16: .long 0 |