From 178d79bccdc97cdaf346a7b87de769a4896df7eb Mon Sep 17 00:00:00 2001
From: Greg Haerr <greg@censoft.com>
Date: Wed, 4 Sep 2024 09:52:19 -0600
Subject: [PATCH] [kernel] Calculate then reduce kernel temp startup stack size

---
 elks/arch/i86/kernel/Makefile  |  2 +-
 elks/arch/i86/kernel/divzero.c |  2 +-
 elks/arch/i86/kernel/irq.c     |  7 +++++--
 elks/arch/i86/kernel/irqtab.S  |  4 +++-
 elks/arch/i86/kernel/strace.c  | 15 +++++++++++++++
 elks/include/arch/segment.h    |  1 +
 elks/include/linuxmt/limits.h  |  1 +
 elks/include/linuxmt/trace.h   |  5 +++--
 8 files changed, 30 insertions(+), 7 deletions(-)

diff --git a/elks/arch/i86/kernel/Makefile b/elks/arch/i86/kernel/Makefile
index 9872fa287..81cf65ab5 100644
--- a/elks/arch/i86/kernel/Makefile
+++ b/elks/arch/i86/kernel/Makefile
@@ -40,7 +40,7 @@ OBJS  = strace.o system.o irq.o irqtab.o process.o \
 
 ifeq ($(CONFIG_ARCH_IBMPC), y)
 OBJS += irq-8259.o timer-8254.o
-#OBJS += divzero.o
+OBJS += divzero.o
 endif
 
 ifeq ($(CONFIG_ARCH_PC98), y)
diff --git a/elks/arch/i86/kernel/divzero.c b/elks/arch/i86/kernel/divzero.c
index 2fc76d0e1..efee180aa 100644
--- a/elks/arch/i86/kernel/divzero.c
+++ b/elks/arch/i86/kernel/divzero.c
@@ -8,7 +8,7 @@
  * 19 Aug 24 Greg Haerr
  */
 
-static char div0msg[] = { "Divide by zero\n" };
+static char div0msg[] = { "Divide fault\n" };
 
 void div0_handler(int i, struct pt_regs *regs)
 {
diff --git a/elks/arch/i86/kernel/irq.c b/elks/arch/i86/kernel/irq.c
index c44217ef5..66aef3853 100644
--- a/elks/arch/i86/kernel/irq.c
+++ b/elks/arch/i86/kernel/irq.c
@@ -125,12 +125,15 @@ void INITPROC irq_init(void)
 
 #ifdef CONFIG_ARCH_IBMPC
     /* catch INT 0 divide by zero/divide overflow hardware fault */
-    /*irq_action[IDX_DIVZERO] = div0_handler;
-      int_handler_add(IDX_DIVZERO, 0x00, _irqit);*/
+#if 1
     /* install direct panic-only DIV fault handler until known that
      * the _irqit version doesn't overwrite the stack
      */
     int_handler_add(IDX_DIVZERO, 0x00, div0_handler_panic);
+#else
+    irq_action[IDX_DIVZERO] = div0_handler;
+    int_handler_add(IDX_DIVZERO, 0x00, _irqit);
+#endif
 #endif
 
 #if defined(CONFIG_TIMER_INT0F) || defined(CONFIG_TIMER_INT1C)
diff --git a/elks/arch/i86/kernel/irqtab.S b/elks/arch/i86/kernel/irqtab.S
index d6c0cb7a3..88645ba87 100644
--- a/elks/arch/i86/kernel/irqtab.S
+++ b/elks/arch/i86/kernel/irqtab.S
@@ -424,6 +424,7 @@ div0_handler_panic:
 	.data
 	.global	_gint_count
 	.global	endistack
+	.global	endtstack
 	.global	istack
 	.global	tstack
 	.extern	current
@@ -445,5 +446,6 @@ endistack:
 	.skip ISTACK_BYTES,0	// interrupt stack
 istack:
 
-	.skip 256,0		// startup temp stack
+endtstack:
+	.skip TSTACK_BYTES,0	// startup temp stack
 tstack:
diff --git a/elks/arch/i86/kernel/strace.c b/elks/arch/i86/kernel/strace.c
index 865aae091..f85044d06 100644
--- a/elks/arch/i86/kernel/strace.c
+++ b/elks/arch/i86/kernel/strace.c
@@ -183,4 +183,19 @@ void trace_end(unsigned int retval)
         check_kstack(n);
 }
 
+#if UNUSED
+void check_tstack(void)
+{
+    int i;
+
+    /* calc temp stack usage */
+    for (i=0; i<TSTACK_BYTES/2; i++) {
+        if (endtstack[i] != 0)
+            break;
+    }
+    i = (TSTACK_BYTES/2 - i) << 1;
+    printk("tstack usage %d\n", i);
+}
+#endif
+
 #endif /* CONFIG_TRACE */
diff --git a/elks/include/arch/segment.h b/elks/include/arch/segment.h
index 919fd6749..162b7e3e8 100644
--- a/elks/include/arch/segment.h
+++ b/elks/include/arch/segment.h
@@ -6,6 +6,7 @@
 extern seg_t kernel_cs, kernel_ds;
 extern short *_endtext, *_endftext, *_enddata, *_endbss;
 extern short endistack[];
+extern short endtstack[];
 extern unsigned int heapsize;
 
 #endif
diff --git a/elks/include/linuxmt/limits.h b/elks/include/linuxmt/limits.h
index 7f54fe267..5b27acba8 100644
--- a/elks/include/linuxmt/limits.h
+++ b/elks/include/linuxmt/limits.h
@@ -17,6 +17,7 @@
 #endif
 
 #define ISTACK_BYTES    512     /* Size of interrupt stack */
+#define TSTACK_BYTES    128     /* Size of temp startup stack */
 
 #define KSTACK_GUARD    100     /* bytes before CHECK_KSTACK overflow warning */
 
diff --git a/elks/include/linuxmt/trace.h b/elks/include/linuxmt/trace.h
index f8628e0c9..90cb07192 100644
--- a/elks/include/linuxmt/trace.h
+++ b/elks/include/linuxmt/trace.h
@@ -45,8 +45,9 @@
 #ifndef __ASSEMBLER__
 extern int tracing;
 
-extern void trace_begin(void);
-extern void trace_end(unsigned int retval);
+void trace_begin(void);
+void trace_end(unsigned int retval);
+void check_tstack(void);
 #endif
 
 #endif