From af2ed201b1d4ede6fc9d4ba2a35b37b5425393c5 Mon Sep 17 00:00:00 2001
From: Alan Cox <alan@linux.intel.com>
Date: Tue, 11 Dec 2018 18:06:08 +0000
Subject: [PATCH] thunked: fix stack handling bug in the pre-emption path

---
 Kernel/lowlevel-z80-thunked.s       | 10 +++++++---
 Kernel/platform-cromemco/kernel.def |  4 ++++
 Kernel/platform-sam/kernel.def      |  4 ++++
 Kernel/platform-sc108/kernel.def    |  3 +++
 4 files changed, 18 insertions(+), 3 deletions(-)

diff --git a/Kernel/lowlevel-z80-thunked.s b/Kernel/lowlevel-z80-thunked.s
index efe65402..4ebdff65 100644
--- a/Kernel/lowlevel-z80-thunked.s
+++ b/Kernel/lowlevel-z80-thunked.s
@@ -86,7 +86,7 @@ _doexec:
 	ld sp,hl
 	ex de,hl
 	ld de,#PROGLOAD
-	ld a,(U_DATA__U_PAGE+1)	; pass high page to trampoline
+	ld a,(U_DATA__U_PAGE+HIGHPAGE) ; pass high page to trampoline
 	jp _platform_doexec	; jump into the low memory stub
 
 ;
@@ -158,7 +158,7 @@ syscall_return:
 	exx
 	; Return page for caller (may not be the page we can in on if we
 	; swapped
-	ld a,(U_DATA__U_PAGE+1)
+	ld a,(U_DATA__U_PAGE+HIGHPAGE)
 	ret
 signal_path:
 	ld h,a		; save signal number
@@ -234,7 +234,7 @@ no_sig:
 	xor a
 	ld (_int_disabled),a
 	ld e,a
-	ld a,(U_DATA__U_PAGE+1)
+	ld a,(U_DATA__U_PAGE+HIGHPAGE)
 intret:
 	ret
 
@@ -317,6 +317,10 @@ intret2:
 	; The istack was lost but that is ok as we saved the return onto the
 	; kernel stack, so when we finally ret we end up in the right place
 	ld sp,#kstack_top - 2		; saved return address
+
+	ld hl,(U_DATA__U_SYSCALL_SP)
+	ld (istack_switched_sp),hl
+
 	; Now continue on the interrupt return path
 	; looking for signals
 	jr intsig
diff --git a/Kernel/platform-cromemco/kernel.def b/Kernel/platform-cromemco/kernel.def
index def2cec1..939d0b7b 100644
--- a/Kernel/platform-cromemco/kernel.def
+++ b/Kernel/platform-cromemco/kernel.def
@@ -21,3 +21,7 @@ CONFIG_SWAP		    .equ 0
 .macro HIGH
 		.area _COMMONMEM
 .endm
+
+; We only have a single page entry
+
+HIGHPAGE		    .equ 0
\ No newline at end of file
diff --git a/Kernel/platform-sam/kernel.def b/Kernel/platform-sam/kernel.def
index 50f075fa..d00b87bb 100644
--- a/Kernel/platform-sam/kernel.def
+++ b/Kernel/platform-sam/kernel.def
@@ -20,3 +20,7 @@ Z80_TYPE		    .equ 1
 .macro HIGH
 		.area _HIGH
 .endm
+
+; We keep the low and high bytes of the 32K map in the two adjacent bytes
+;
+HIGHPAGE		    .equ 1
\ No newline at end of file
diff --git a/Kernel/platform-sc108/kernel.def b/Kernel/platform-sc108/kernel.def
index 35fe066b..37a5db61 100644
--- a/Kernel/platform-sc108/kernel.def
+++ b/Kernel/platform-sc108/kernel.def
@@ -44,3 +44,6 @@ NBUFS		.equ	4
 .macro HIGH
 		.area _COMMONMEM
 .endm
+
+HIGHPAGE	.equ	0	; We only have 1 page byte and the low page
+				; isn't used
-- 
2.34.1