From 6c35a525da16c6147600cd8613a9b60bb793b934 Mon Sep 17 00:00:00 2001 From: Michael Brown Date: Mon, 19 Apr 2010 22:22:11 +0100 Subject: [PATCH] [prefix] Use flat real mode for access to high memory Use flat real mode rather than 16-bit protected mode for access to high memory during installation. This simplifies the code by reducing the number of CPU modes we need to think about, and also increases the amount of code in common between the normal and (somewhat hypothetical) KEEP_IT_REAL methods of operation. Signed-off-by: Michael Brown --- src/arch/i386/prefix/libprefix.S | 206 ++++++++++++------------------- 1 file changed, 79 insertions(+), 127 deletions(-) diff --git a/src/arch/i386/prefix/libprefix.S b/src/arch/i386/prefix/libprefix.S index ecef56d8..4decb013 100644 --- a/src/arch/i386/prefix/libprefix.S +++ b/src/arch/i386/prefix/libprefix.S @@ -233,156 +233,128 @@ print_kill_line: .size print_kill_line, . - print_kill_line /**************************************************************************** - * pm_call (real-mode near call) + * flatten_real_mode * - * Call routine in 16-bit protected mode for access to extended memory + * Set up 4GB segment limits * * Parameters: - * %ax : address of routine to call in 16-bit protected mode + * none * Returns: * none * Corrupts: - * %ax - * - * The specified routine is called in 16-bit protected mode, with: - * - * %cs : 16-bit code segment with base matching real-mode %cs - * %ss : 16-bit data segment with base matching real-mode %ss - * %ds,%es,%fs,%gs : 32-bit data segment with zero base and 4GB limit - * + * none **************************************************************************** */ - #ifndef KEEP_IT_REAL /* GDT for protected-mode calls */ .section ".prefix.lib", "awx", @progbits .align 16 -pm_call_vars: -gdt: -gdt_limit: .word gdt_length - 1 -gdt_base: .long 0 +flatten_vars: +flatten_gdt: +flatten_gdt_limit: .word flatten_gdt_length - 1 +flatten_gdt_base: .long 0 .word 0 /* padding */ -pm_cs: /* 16-bit protected-mode flat code segment */ - .equ PM_CS, pm_cs - gdt +flatten_cs: /* 16-bit protected-mode flat code segment */ + .equ FLAT_CS, flatten_cs - flatten_gdt .word 0xffff, 0 .byte 0, 0x9b, 0x8f, 0 -pm_ss: /* 16-bit protected-mode flat stack segment */ - .equ PM_SS, pm_ss - gdt +flatten_ss: /* 16-bit protected-mode flat stack segment */ + .equ FLAT_SS, flatten_ss - flatten_gdt .word 0xffff, 0 .byte 0, 0x93, 0x8f, 0 -pm_ds: /* 32-bit protected-mode flat data segment */ - .equ PM_DS, pm_ds - gdt - .word 0xffff, 0 - .byte 0, 0x93, 0xcf, 0 -gdt_end: - .equ gdt_length, . - gdt - .size gdt, . - gdt +flatten_gdt_end: + .equ flatten_gdt_length, . - flatten_gdt + .size flatten_gdt, . - flatten_gdt .section ".prefix.lib", "awx", @progbits .align 16 -pm_saved_gdt: +flatten_saved_gdt: .long 0, 0 - .size pm_saved_gdt, . - pm_saved_gdt + .size flatten_saved_gdt, . - flatten_saved_gdt - .equ pm_call_vars_size, . - pm_call_vars -#define PM_CALL_VAR(x) ( -pm_call_vars_size + ( (x) - pm_call_vars ) ) + .equ flatten_vars_size, . - flatten_vars +#define FLATTEN_VAR(x) ( -flatten_vars_size + ( (x) - flatten_vars ) ) .section ".prefix.lib", "awx", @progbits .code16 -pm_call: - /* Preserve registers, flags, and RM return point */ +flatten_real_mode: + /* Preserve registers and flags, allocate local variable block */ pushw %bp movw %sp, %bp - subw $pm_call_vars_size, %sp + subw $flatten_vars_size, %sp andw $0xfff0, %sp pushfl + pushl %eax + pushl %edi + pushw %si + pushw %cx pushw %gs pushw %fs pushw %es pushw %ds pushw %ss - pushw %cs - pushw $99f - /* Set up local variable block, and preserve GDT */ - pushw %cx - pushw %si - pushw %di + /* Fill local variable block and preserve GDT */ pushw %ss popw %es - movw $pm_call_vars, %si - leaw PM_CALL_VAR(pm_call_vars)(%bp), %di - movw $pm_call_vars_size, %cx + movw $flatten_vars, %si + leaw FLATTEN_VAR(flatten_vars)(%bp), %di + movw $flatten_vars_size, %cx cs rep movsb - popw %di - popw %si - popw %cx - sgdt PM_CALL_VAR(pm_saved_gdt)(%bp) + sgdt FLATTEN_VAR(flatten_saved_gdt)(%bp) /* Set up GDT bases */ - pushl %eax - pushl %edi xorl %eax, %eax movw %ss, %ax shll $4, %eax movzwl %bp, %edi - addr32 leal PM_CALL_VAR(gdt)(%eax, %edi), %eax - movl %eax, PM_CALL_VAR(gdt_base)(%bp) + addr32 leal FLATTEN_VAR(flatten_gdt)(%eax, %edi), %eax + movl %eax, FLATTEN_VAR(flatten_gdt_base)(%bp) movw %cs, %ax - movw $PM_CALL_VAR(pm_cs), %di + movw $FLATTEN_VAR(flatten_cs), %di call set_seg_base movw %ss, %ax - movw $PM_CALL_VAR(pm_ss), %di + movw $FLATTEN_VAR(flatten_ss), %di call set_seg_base - popl %edi - popl %eax - /* Switch CPU to protected mode and load up segment registers */ - pushl %eax + /* Switch temporarily to protected mode and set segment registers */ + pushw %cs + pushw $2f cli - data32 lgdt PM_CALL_VAR(gdt)(%bp) + data32 lgdt FLATTEN_VAR(flatten_gdt)(%bp) movl %cr0, %eax orb $CR0_PE, %al movl %eax, %cr0 - ljmp $PM_CS, $1f -1: movw $PM_SS, %ax + ljmp $FLAT_CS, $1f +1: movw $FLAT_SS, %ax movw %ax, %ss - movw $PM_DS, %ax movw %ax, %ds movw %ax, %es movw %ax, %fs movw %ax, %gs - popl %eax - - /* Call PM routine */ - call *%ax - - /* Set real-mode segment limits on %ds, %es, %fs and %gs */ - movw %ss, %ax - movw %ax, %ds - movw %ax, %es - movw %ax, %fs - movw %ax, %gs - - /* Return CPU to real mode */ movl %cr0, %eax andb $0!CR0_PE, %al movl %eax, %cr0 + lret +2: /* lret will ljmp to here */ - /* Restore registers and flags */ - lret /* will ljmp to 99f */ -99: popw %ss + /* Restore GDT, registers and flags */ + data32 lgdt FLATTEN_VAR(flatten_saved_gdt)(%bp) + popw %ss popw %ds popw %es popw %fs popw %gs - data32 lgdt PM_CALL_VAR(pm_saved_gdt)(%bp) + popw %cx + popw %si + popl %edi + popl %eax popfl movw %bp, %sp popw %bp ret - .size pm_call, . - pm_call + .size flatten_real_mode, . - flatten_real_mode set_seg_base: rolw $4, %ax @@ -396,7 +368,7 @@ set_seg_base: #endif /* KEEP_IT_REAL */ /**************************************************************************** - * copy_bytes (real-mode or 16-bit protected-mode near call) + * copy_bytes * * Copy bytes * @@ -411,6 +383,7 @@ set_seg_base: * None **************************************************************************** */ +#if ! COMPRESS .section ".prefix.lib", "awx", @progbits .code16 copy_bytes: @@ -419,9 +392,10 @@ copy_bytes: popl %ecx ret .size copy_bytes, . - copy_bytes +#endif /* COMPRESS */ /**************************************************************************** - * install_block (real-mode near call) + * install_block * * Install block to specified address * @@ -439,39 +413,22 @@ copy_bytes: .section ".prefix.lib", "awx", @progbits .code16 install_block: - -#ifdef KEEP_IT_REAL - /* Preserve registers */ pushw %ds pushw %es pushl %ecx pushl %edi - /* Convert %esi and %edi to segment registers */ + /* Convert %esi and %edi to %ds:esi and %es:edi */ shrl $4, %esi movw %si, %ds xorw %si, %si + shll $4, %esi shrl $4, %edi movw %di, %es xorw %di, %di + shll $4, %edi -#else /* KEEP_IT_REAL */ - - /* Call self in protected mode */ - pushw %ax - movw $1f, %ax - call pm_call - popw %ax - ret -1: - /* Preserve registers */ - pushl %ecx - pushl %edi - -#endif /* KEEP_IT_REAL */ - - #if COMPRESS /* Decompress source to destination */ call decompress16 @@ -492,33 +449,22 @@ install_block: addl $0xf, %esi andl $~0xf, %esi - -#ifdef KEEP_IT_REAL - /* Convert %ds:esi back to a physical address */ - movzwl %ds, %cx + xorl %ecx, %ecx + movw %ds, %cx shll $4, %ecx addl %ecx, %esi - /* Restore registers */ + /* Restore registers and return */ popl %edi popl %ecx popw %es popw %ds - -#else /* KEEP_IT_REAL */ - - /* Restore registers */ - popl %edi - popl %ecx - -#endif - ret .size install_block, . - install_block - + /**************************************************************************** - * alloc_basemem (real-mode near call) + * alloc_basemem * * Allocate space for .text16 and .data16 from top of base memory. * Memory is allocated using the BIOS free base memory counter at @@ -568,7 +514,7 @@ alloc_basemem: .size alloc_basemem, . - alloc_basemem /**************************************************************************** - * free_basemem (real-mode near call) + * free_basemem * * Free space allocated with alloc_basemem. * @@ -620,7 +566,7 @@ hooked_bios_interrupts: .size hooked_bios_interrupts, . - hooked_bios_interrupts /**************************************************************************** - * install (real-mode near call) + * install * * Install all text and data segments. * @@ -655,7 +601,7 @@ install: .size install, . - install /**************************************************************************** - * install_prealloc (real-mode near call) + * install_prealloc * * Install all text and data segments. * @@ -680,6 +626,11 @@ install_prealloc: /* Sanity: clear the direction flag asap */ cld +#ifndef KEEP_IT_REAL + /* Flatten real mode */ + call flatten_real_mode +#endif + /* Calculate physical address of payload (i.e. first source) */ testl %esi, %esi jnz 1f @@ -732,16 +683,15 @@ install_prealloc: /* Copy code to new location */ pushl %edi - pushw %ax - movw $copy_bytes, %ax - call pm_call - popw %ax + xorw %ax, %ax + movw %ax, %es + es rep addr32 movsb popl %edi /* Initialise librm at new location */ lcall *init_librm_vector - #endif + /* Restore registers */ popw %es popw %ds @@ -749,7 +699,9 @@ install_prealloc: ret .size install_prealloc, . - install_prealloc - /* Vectors for far calls to .text16 functions */ + /* Vectors for far calls to .text16 functions. Must be in + * .data16, since .prefix may not be writable. + */ .section ".data16", "aw", @progbits #ifdef KEEP_IT_REAL init_libkir_vector: @@ -768,7 +720,7 @@ prot_call_vector: #endif /**************************************************************************** - * uninstall (real-mode near call) + * uninstall * * Uninstall all text and data segments. *