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

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.

kernel/kernel.asm

@@ -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)
 
@@ -213,10 +223,37 @@ cont:           ; Now set up call frame
 %endif
                 mov     [_CPULevel], al
 
-                mov     ax,ss
+initialise_kernel_config:
-                mov     ds,ax
+extern _InitKernelConfig
-                mov     es,ax
+
-                jmp     _FreeDOSmain
+	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
         cpu 8086

kernel/main.c

@@ -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));
+    *p = drv - 1;	/* compatibility with older kernels */
-
-    drv = *p + 1;
-    *(DWORD FAR *)(p+2) = 0;
-  }
-  else
-  {
-    *p = drv - 1;
-    fmemcpy(&InitKernelConfig, &LowKernelConfig, sizeof(InitKernelConfig));
   }
 
   if (drv >= 0x80)