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kernel: copy CONFIG block from UPX help data early in kernel.asm

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Here we depend on the signal instruction that is patched
by exeflat to indicate whether we were compressed. This
replaces the prior check that detected the UPX help data
solely by checking the CONFIG signature at 05E2h.
This commit is contained in:
C. Masloch 2022-05-21 15:17:01 +02:00 committed by Kenneth J Davis
parent b7345d9165
commit 7ff6c06814
2 changed files with 45 additions and 17 deletions
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43
kernel/kernel.asm
View File

@ -56,6 +56,7 @@ entry:
;************************************************************
global _LowKernelConfig
_LowKernelConfig:
config_signature:
db 'CONFIG' ; constant
dw configend-configstart; size of config area
; to be checked !!!
@ -76,6 +77,9 @@ Version_Revision dw 41 ; REVISION_SEQ
Version_Release dw 1 ; 0=release build, >0=svn#
configend:
kernel_config_size: equ configend - config_signature
; must be below-or-equal the size of struct _KernelConfig
; in the file kconfig.h !
;************************************************************
; KERNEL CONFIGURATION AREA END
@ -94,7 +98,10 @@ configend:
cpu 8086 ; (keep initial entry compatible)
global realentry
realentry: ; execution continues here
clc ; this is patched to stc by exeflat
adc byte [cs:use_upx_config], 0
push ax
push bx
@ -107,6 +114,9 @@ realentry: ; execution continues here
pop ax
jmp IGROUP:kernel_start
use_upx_config: db 0
beyond_entry: times 256-(beyond_entry-entry) db 0
; scratch area for data (DOS_PSP)
@ -213,9 +223,36 @@ cont: ; Now set up call frame
%endif
mov [_CPULevel], al
mov ax,ss
mov ds,ax
mov es,ax
initialise_kernel_config:
extern _InitKernelConfig
push ds
pop es ; => DOS data segment (for _BootDrive)
mov ax, ss ; => init data segment
mov si, 60h
mov ds, si ; => entry section
mov si, _LowKernelConfig ; -> our own CONFIG block
; This block is part of what got decompressed if
; the kernel is UPX-compressed. And if UPX was
; used in .SYS mode then the first several words
; are overwritten with pseudo device header fields.
cmp byte [use_upx_config], 0 ; from UPX ?
je .notupx ; no, use own CONFIG block -->
mov si, 5Eh
mov ds, si
mov si, 2 ; -> CONFIG block of compressed entry
mov bl, [0] ; 05E0h has the boot load unit
mov byte [es:_BootDrive], bl ; overwrite the value in DOS data segment
.notupx:
mov es, ax ; => init data segment
mov di, _InitKernelConfig ; -> init's CONFIG block buffer
mov cx, kernel_config_size / 2 ; size that we support
rep movsw ; copy it over
%if kernel_config_size & 1
movsb ; allow odd size
%endif
mov ds, ax ; => init data segment
jmp _FreeDOSmain
%if XCPU != 86

15
kernel/main.c
View File

@ -44,8 +44,6 @@ static char copyright[] =
"GNU General Public License as published by the Free Software Foundation;\n"
"either version 2, or (at your option) any later version.\n";
struct _KernelConfig InitKernelConfig BSS_INIT({0});
STATIC VOID InitIO(void);
STATIC VOID update_dcb(struct dhdr FAR *);
@ -70,6 +68,8 @@ __segment DosTextSeg = 0;
struct lol FAR *LoL = &DATASTART;
struct _KernelConfig InitKernelConfig = { 0xFF };
VOID ASMCFUNC FreeDOSmain(void)
{
unsigned char drv;
@ -92,17 +92,8 @@ VOID ASMCFUNC FreeDOSmain(void)
drv = LoL->BootDrive + 1;
p = MK_FP(0, 0x5e0);
if (fmemcmp(p+2,"CONFIG",6) == 0) /* UPX */
{
fmemcpy(&InitKernelConfig, p+2, sizeof(InitKernelConfig));
drv = *p + 1;
*(DWORD FAR *)(p+2) = 0;
}
else
{
*p = drv - 1;
fmemcpy(&InitKernelConfig, &LowKernelConfig, sizeof(InitKernelConfig));
*p = drv - 1; /* compatibility with older kernels */
}
if (drv >= 0x80)