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-rw-r--r--bcopy32.inc128
1 files changed, 82 insertions, 46 deletions
diff --git a/bcopy32.inc b/bcopy32.inc
index d0f8a462..056f29bd 100644
--- a/bcopy32.inc
+++ b/bcopy32.inc
@@ -71,6 +71,13 @@ bcopy_gdt:
desc TSS
dw 104-1, DummyTSS ; 30h 32-bit task state segment
dd 00008900h ; present, dpl 0, 104 bytes @DummyTSS
+
+ ; 16-bit stack segment, which may have a different
+ ; base from DS16 (e.g. if we're booted from PXELINUX)
+ desc SS16
+ dd 0000ffffh ; 38h Data segment, use16, read/write,
+ dd 00009300h ; present, dpl 0, cover 64K
+
bcopy_gdt_size: equ $-bcopy_gdt
;
@@ -86,13 +93,33 @@ bcopy_gdt_size: equ $-bcopy_gdt
; Outputs:
; ESI - first byte after source (garbage if ESI == -1 on entry)
; EDI - first byte after target
-; ECX - zero
;
-bcopy: push eax
- push ebx
- push esi
- push edi
- push ecx
+bcopy: pushad
+ mov bx,pm_bcopy
+ call simple_pm_call
+ popad
+ add edi,ecx
+ add esi,ecx
+ ret
+
+;
+; This routine is used to invoke a simple routine in 16-bit protected
+; mode (with 32-bit DS and ES, and working 16-bit stack.)
+; Note that all segment registers including CS, except possibly SS,
+; are zero-based in the protected-mode routine.
+;
+; No interrupt thunking services are provided; interrupts are disabled
+; for the duration of the routine. Don't run for too long at a time.
+;
+; Inputs:
+; BX - routine to execute
+; ECX, EDX, EBP, ESI and EDI passed to the called routine
+;
+; Outputs:
+; EAX, EBX destroyed
+; All other registers as returned from called function
+;
+simple_pm_call:
pushf ; Saves, among others, the IF flag
push ds
push es
@@ -102,36 +129,73 @@ bcopy: push eax
cli
call enable_a20
- mov byte [bcopy_gdt.TSS+5],89h ; Mark TSS unbusy
+ mov byte [cs:bcopy_gdt.TSS+5],89h ; Mark TSS unbusy
- mov bx,ss ; Save the stack segment value!
+ ; Convert the stack segment to a base
+ xor eax,eax
+ mov ax,ss
+ shl eax,4
+ or eax,93000000h
+ mov [cs:bcopy_gdt.SS16+2],eax
+ push ss ; Save real-mode SS selector
+
o32 lgdt [cs:bcopy_gdt]
mov eax,cr0
or al,1
mov cr0,eax ; Enter protected mode
jmp PM_CS16:.in_pm
+.in_pm:
+ mov ax,PM_SS16 ; Make stack usable
+ mov ss,ax
-.in_pm: mov ax,PM_DS16_4G ; Data segment selector
+ mov al,PM_DS16_4G ; Data segment selector
mov es,ax
mov ds,ax
- ; Set ss, fs, and gs, in case we're on a virtual machine
- ; running on Intel VT hardware -- it can't deal with a
- ; partial transition, for no good reason. However,
- ; ss is NOT zero in general, so we have to preserve
- ; the value.
+ ; Set fs, gs, tr, and ldtr in case we're on a virtual
+ ; machine running on Intel VT hardware -- it can't
+ ; deal with a partial transition, for no good reason.
mov al,PM_DS16_RM ; Real-mode-like segment
mov fs,ax
mov gs,ax
- mov ss,ax
-
mov al,PM_TSS ; Intel VT really doesn't want
ltr ax ; an invalid TR and LDTR, so give
xor ax,ax ; it something that it can use...
lldt ax ; (sigh)
+ call bx ; Call actual routine
+
+.exit:
+ mov ax,PM_DS16_RM ; "Real-mode-like" data segment
+ mov es,ax
+ mov ds,ax
+
+ pop bx ; Previous value for ss
+
+ mov eax,cr0
+ and al,~1
+ mov cr0,eax ; Disable protected mode
+ jmp 0:.in_rm
+
+.in_rm: ; Back in real mode
+ mov ss,bx
+ pop gs
+ pop fs
+ pop es
+ pop ds
+ call disable_a20
+
+ popf ; Re-enables interrupts
+ ret
+
+;
+; pm_bcopy:
+;
+; This is the protected-mode core of the "bcopy" routine.
+;
+pm_bcopy:
cmp esi,-1
je .bzero
@@ -147,7 +211,7 @@ bcopy: push eax
mov cl,al ; Copy any fractional dword
a32 rep movsb
- jmp .exit
+ ret
.reverse:
std ; Reverse copy
@@ -166,7 +230,7 @@ bcopy: push eax
a32 rep movsd
cld
- jmp .exit
+ ret
.bzero:
xor eax,eax
@@ -177,34 +241,6 @@ bcopy: push eax
mov cx,si ; Write fractional dword
a32 rep stosb
- ; jmp .exit
-
-.exit:
- mov ax,PM_DS16_RM ; "Real-mode-like" data segment
- mov es,ax
- mov ds,ax
-
- mov eax,cr0
- and al,~1
- mov cr0,eax ; Disable protected mode
- jmp 0:.in_rm
-
-.in_rm: ; Back in real mode
- mov ss,bx
- pop gs
- pop fs
- pop es
- pop ds
- call disable_a20
-
- popf ; Re-enables interrupts
- pop eax
- pop edi
- pop esi
- add edi,eax
- add esi,eax
- pop ebx
- pop eax
ret
;