Add support for using a shuffle descriptor to bzero rather than bcopy

When source address is set to -1, do a bzero instead of a bcopy.

diff --git a/bcopy32.inc b/bcopy32.inc
index 11bdae0..4448c9e 100644 (file)
--- a/bcopy32.inc
+++ b/bcopy32.inc
@@ -58,27 +58,32 @@ bcopy_gdt_size:     equ $-bcopy_gdt
 ;      32-bit copy, overlap safe
 ;
 ; Inputs:
-;      ESI     - source pointer
+;      ESI     - source pointer (-1 means do bzero rather than bcopy)
 ;      EDI     - target pointer
 ;      ECX     - byte count
 ;      DF      - zero
 ;
 ; Outputs:
-;      ESI     - first byte after source
+;      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
                pushf                   ; Saves, among others, the IF flag
                push ds
                push es
+               push fs
+               push gs
 
                cli
                call enable_a20
 
+               mov bx,ss               ; Save the stack segment value!
+
                o32 lgdt [cs:bcopy_gdt]
                mov eax,cr0
                or al,1
@@ -89,10 +94,19 @@ bcopy:              push eax
                mov es,ax
                mov ds,ax
 
-               ; Don't mess with ss, fs, and gs.  They are never changed
-               ; and should be able to make it back out of protected mode.
-               ; This works because (and only because) we don't take
-               ; interrupt in protected mode.
+               ; 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.
+
+               mov ax,18h              ; Real-mode-like segment
+               mov fs,ax
+               mov gs,ax
+               mov ss,ax
+
+               cmp esi,-1
+               je .bzero
 
                cmp esi,edi             ; If source > destination, we might
                ja .reverse             ; have to copy backwards
@@ -125,6 +139,18 @@ bcopy:             push eax
                a32 rep movsd
 
                cld
+               jmp .exit
+
+.bzero:
+               xor eax,eax
+               mov si,cx               ; Save low bits
+               and si,3
+               shr ecx,2
+               a32 rep stosd
+
+               mov cx,si               ; Write fractional dword
+               a32 rep stosb
+               ; jmp .exit
 
 .exit:
                mov ax,18h              ; "Real-mode-like" data segment
@@ -137,6 +163,9 @@ bcopy:              push eax
                jmp 0:.in_rm
 
 .in_rm:                ; Back in real mode
+               mov ss,bx
+               pop gs
+               pop fs
                pop es
                pop ds
                call disable_a20
@@ -147,6 +176,7 @@ bcopy:              push eax
                pop esi
                add edi,eax
                add esi,eax
+               pop ebx
                pop eax
                ret
 

diff --git a/comboot.doc b/comboot.doc
index 1d4a164..b61fb08 100644 (file)
--- a/comboot.doc
+++ b/comboot.doc
@@ -576,6 +576,10 @@ AX=0012h [3.05] Cleanup, shuffle and boot
 
        The copies are overlap-safe, like memmove().
 
+       Starting in version 3.40, if the source address is -1
+       (FFFFFFFFh) then the block specified by the destination
+       address and the length is set to all zero.
+
        Normal boot sectors expect DL to contain the drive number,
        and, for hard drives (DL >= 80h) DS:SI to contain a pointer to
        the 16-byte partition table entry.  The memory between