From 98ce65d99afe369f335f82e8800c9b0d56934d2a Mon Sep 17 00:00:00 2001
From: Stas Sergeev <stsp2@yandex.ru>
Date: Sat, 14 Oct 2023 02:28:59 +0500
Subject: [PATCH] init DOS_PSP with PGROUP [#172][skip CI]

We used to have DOS_PSP=cs, but now we have ELF headers in DOS space.
And as we use tiny model, cs:0 inevitably points to them.
To not overwrite them with PSP, move DOS_PSP var to kernel.asm and
initialize it with PGROUP.
This patch makes PGROUP no longer equal to other segments, so this
needs a proper segelf support. This can't be done in a master branch
where we relocate by a hard-coded value only (0x60).
So this patch shows a clear advantage of the segelf scheme usage.

Note that even the part of this patch, eg aligning PSP section to
0x100, cannot be back-ported to master because there we store PSP
at cs:0 regardless of the linker script, and overwrite whatever
is there. And there are the ELF headers now, since commit 95432f82.
Which probably shouldn't have been back-ported to master as a start.
---
 fdpp/kernel.ld    | 11 +++++++----
 kernel/glob_asm.h |  1 +
 kernel/kernel.asm |  2 ++
 kernel/main.c     |  3 ---
 4 files changed, 10 insertions(+), 7 deletions(-)

diff --git a/fdpp/kernel.ld b/fdpp/kernel.ld
index 4a55230f..94690983 100644
--- a/fdpp/kernel.ld
+++ b/fdpp/kernel.ld
@@ -5,22 +5,25 @@ SECTIONS
     _LOADADDR = DEFINED(loadaddr) ? loadaddr : .;
     /* these GROUPs play the same role as GROUPS (segments) in OMF */
     /* TINY model, all segments are equal */
-    _PGROUP = ABSOLUTE(.);
     _LGROUP = ABSOLUTE(.);
     _DGROUP = ABSOLUTE(.);
     _IGROUP = ABSOLUTE(.);
-    _PGROUP~ = . + _LOADADDR;
     _LGROUP~ = . + _LOADADDR;
     _DGROUP~ = . + _LOADADDR;
     _IGROUP~ = . + _LOADADDR;
 
+    . = SIZEOF_HEADERS;
+    . = ALIGN(0x100);
     /* Target PSP section.  */
-    .ptext SIZEOF_HEADERS : {
+    .ptext : {
+		_PGROUP = ABSOLUTE(.);
+		_PGROUP~ = . + _LOADADDR;
 		*(PSP)
+		. = ALIGN(0x100);
     }
 
     /* Target low data+text sections.  */
-    .ltext 0x200 : {
+    .ltext : {
 		*(_IRQTEXT)
 		*(_LOWTEXT)
 		*(_IO_TEXT)
diff --git a/kernel/glob_asm.h b/kernel/glob_asm.h
index fcedbd16..b4e903d2 100644
--- a/kernel/glob_asm.h
+++ b/kernel/glob_asm.h
@@ -1,5 +1,6 @@
 /* grep "ASM " globals.h | grep "extern" | grep ";" | sed 's/extern \(.\+\) ASM \(.\+\);/__ASM(\1, \2) SEMIC/' */
 
+__ASM(UWORD, DOS_PSP) SEMIC
 __ASM(UWORD, NetBios) SEMIC
 __ASM(BYTE *, net_name) SEMIC
 __ASM(BYTE, net_set_count) SEMIC
diff --git a/kernel/kernel.asm b/kernel/kernel.asm
index 1a639e24..770e2c14 100644
--- a/kernel/kernel.asm
+++ b/kernel/kernel.asm
@@ -778,6 +778,8 @@ begin_hma:
 ; to minimize relocations
                 global _DGROUP_
 _DGROUP_        dw DGROUP
+                global _DOS_PSP
+_DOS_PSP        dw PGROUP
 
 %ifdef WATCOM
 ;               32 bit multiplication + division
diff --git a/kernel/main.c b/kernel/main.c
index dd7c5b83..3211eeaf 100644
--- a/kernel/main.c
+++ b/kernel/main.c
@@ -73,8 +73,6 @@ __segment DosTextSeg = 0;
 
 #endif
 
-UWORD DOS_PSP;
-
 ASMREF(struct lol) LoL = __ASMADDR(DATASTART);
 struct _bprm bprm;
 #define TEXT_SIZE (_InitTextEnd - _HMATextStart)
@@ -91,7 +89,6 @@ VOID ASMCFUNC FreeDOSmain(void)
   DosDataSeg = (__segment) & DATASTART;
   DosTextSeg = (__segment) & prn_dev;
 #endif
-  DOS_PSP = _CS;
   /* back up kernel code to the top of ram */
   lpTop = MK_FP(_SS - (TEXT_SIZE + 15) / 16, 0);
   fmemcpy(lpTop, _HMATextStart, TEXT_SIZE);