From 0ec2016f80ffb5971362559b98b10744bb5bf893 Mon Sep 17 00:00:00 2001
From: Wojtek Kosior <kwojtus@protonmail.com>
Date: Tue, 31 Dec 2019 18:54:28 +0100
Subject: split stack into irq, fiq and supervisor stacks; add proper handling
 of those in interrupt handlers (asm code)

---
 interrupt_vector.S | 25 ++++++++++++++-----------
 kernel_stage2.ld   | 22 +++++++++++++++++++---
 memory.h           | 18 +++++++++++++++---
 3 files changed, 48 insertions(+), 17 deletions(-)

diff --git a/interrupt_vector.S b/interrupt_vector.S
index 88b32bf..af80eec 100644
--- a/interrupt_vector.S
+++ b/interrupt_vector.S
@@ -9,39 +9,42 @@ _interrupt_vectors:
 	b fiq_handler_caller
 	
 reset_handler_caller:
-	ldr sp, =_stack_top
+	ldr sp, =_supervisor_stack_top
 	ldr r5, =reset_handler
 	bx r5
 	
 undef_handler_caller:
-	ldr sp, =_stack_top
+	ldr sp, =_supervisor_stack_top
 	ldr r5, =undefined_instruction_vector
 	bx r5
 
 svc_handler_caller:
-	ldr sp, =_stack_top
+	ldr sp, =_supervisor_stack_top
+	push {r5, lr}
 	ldr r5, =supervisor_call_handler
-	push {lr}
 	blx r5
-	ldm sp!, {pc} ^
+	ldm sp!, {r5, pc} ^
 	
 abort_handler_caller:
-	ldr sp, =_stack_top
+	ldr sp, =_supervisor_stack_top
 	ldr r5, =abort_handler
 	bx r5
 
 generic_handler_caller:
-	ldr sp, =_stack_top
+	ldr sp, =_supervisor_stack_top
 	ldr r5, =generic_handler
 	bx r5
 
 irq_handler_caller:
-	ldr sp, =_stack_top
-	ldr r5, =irq_handler
-	bx r5
+	ldr sp, =_irq_stack_top
+	sub lr, #4
+	push {r0-r3, lr}
+	ldr r3, =irq_handler
+	blx r3
+	ldm sp!, {r0-r3, pc} ^
 
 fiq_handler_caller:
-	ldr sp, =_stack_top
+	ldr sp, =_fiq_stack_top
 	ldr r5, =fiq_handler
 	bx r5
 	
diff --git a/kernel_stage2.ld b/kernel_stage2.ld
index a3df063..15b61ec 100644
--- a/kernel_stage2.ld
+++ b/kernel_stage2.ld
@@ -56,8 +56,24 @@ SECTIONS
 	{
 		_stack_start = .;
 		
-		. = . + MMU_SECTION_SIZE;
-
-		_stack_top = .;
+		_fiq_stack_start = .;
+		
+		. = . + (1 << 18);
+		
+		_fiq_stack_top = .;
+		
+		_irq_stack_start = .;
+		
+		. = . + (1 << 18);
+		
+		_irq_stack_top = .;
+		
+		_supervisor_stack_start = .;
+		
+		. = . + (1 << 19);
+		
+		_supervisor_stack_top = .;
+		
+		_stack_end = .;
 	}
 }
diff --git a/memory.h b/memory.h
index c7952f0..bdeba52 100644
--- a/memory.h
+++ b/memory.h
@@ -28,7 +28,13 @@ extern char _translation_table_end;
 extern char _sections_list_start;
 extern char _sections_list_end;
 extern char _stack_start;
-extern char _stack_top;
+extern char _fiq_stack_start;
+extern char _fiq_stack_top;
+extern char _irq_stack_start;
+extern char _irq_stack_top;
+extern char _supervisor_stack_start;
+extern char _supervisor_stack_top;
+extern char _stack_end;
 
 #define KERNEL_START ((size_t) &__start) // this is 0x0
 #define KERNEL_END   ((size_t) &__end)
@@ -43,8 +49,14 @@ extern char _stack_top;
 
 // first section after the translation table is left unused;
 // the next section is used as the stack
-#define STACK_START ((size_t) &_stack_start)
-#define STACK_END   ((size_t) &_stack_top)
+#define STACK_START            ((size_t) &_stack_start)
+#define FIQ_STACK_START        ((size_t) &_fiq_stack_start)
+#define FIQ_STACK_END          ((size_t) &_fiq_stack_top)
+#define IRQ_STACK_START        ((size_t) &_irq_stack_start)
+#define IRQ_STACK_END          ((size_t) &_irq_stack_top)
+#define SUPERVISOR_STACK_START ((size_t) &_supervisor_stack_start)
+#define SUPERVISOR_STACK_END   ((size_t) &_supervisor_stack_top)
+#define STACK_END              ((size_t) &_stack_end)
 
 #define PRIVILEGED_MEMORY_END STACK_END
 
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