Improved context saving.

include/proc.h

@@ -9,6 +9,16 @@
 #ifndef PROC_H
 #define PROC_H
 
+#ifdef __ASSEMBLER__
+
+#define SAVE_CONTEXT \
+	push {r0, r14};\
+	mov r0, lr;\
+	bl save_context;\
+	pop {r0, r14};
+
+#else
+
 #include <vm.h>
 #include <types.h>
 
@@ -90,6 +100,8 @@ void proc_expand_memory(struct Process *proc, int page_count);
 void proc_shrink_memory(struct Process *proc, int page_count);
 bool proc_load(struct Process *proc, char **proc_image, int page_count);
 void proc_start(struct Process *proc);
+void set_current_process(struct Process *proc);
+int *get_current_context(void);
 
 /* scheduler.c */
 void scheduler_init(void);
@@ -105,3 +117,4 @@ int syscall_fork(void);
 int syscall_exec(int id);
 
 #endif
+#endif

kernel/proc/build.mk

@@ -1,6 +1,7 @@
 PROC_DIR = kernel/proc
 
 OBJS += $(PROC_DIR)/proc.o
+OBJS += $(PROC_DIR)/save_context.o
 OBJS += $(PROC_DIR)/scheduler.o
 OBJS += $(PROC_DIR)/syscall_exit.o
 OBJS += $(PROC_DIR)/syscall_getpid.o

kernel/proc/proc.c

@@ -12,7 +12,6 @@ __attribute__((__aligned__(SECTION_TABLE_ALIGNMENT)))
 struct SectionTableEntry process_vm[PROCESS_COUNT_MAX][4096];
 
 struct Process *current_process = NULL;
-int *current_context;
 
 /* proc_init initializes the process sub-system. */
 void proc_init(void)
@@ -176,7 +175,6 @@ bool proc_load(struct Process *proc, char **proc_image, int page_count)
 void proc_start(struct Process *proc)
 {
 	current_process = proc;
-	current_context = proc->context;
 
 	set_translation_table_base((uint32_t) V2P(proc->vm));
 
@@ -186,3 +184,8 @@ void proc_start(struct Process *proc)
 
 	switch_to_context(proc->context);
 }
+
+int *get_current_context(void)
+{
+	return current_process->context;
+}

kernel/proc/save_context.S

@@ -0,0 +1,34 @@
+
+.global save_context
+save_context:
+	push {r0-r12, r14}
+
+	/* return address of process is passed in r0 */
+	mov r14, r0
+
+	/* load address of context array for current process into r0 */
+	push {r1-r12, r14}
+	bl get_current_context
+	pop {r1-r12, r14}
+
+	/* if no process is active, return */
+	cmpeq r0, #0
+	beq save_context_return
+
+	/* store cpsr */
+	push {r1}
+	mrs r1, spsr
+	str r1, [r0]
+	pop {r1}
+
+	/* store return address */
+	add r0, #4
+	str r14, [r0]
+
+	/* store the rest */
+	add r0, #8
+	stmia r0, {r1-r14}^
+
+save_context_return:
+	pop {r0-r12, r14}
+	mov pc, lr

kernel/startup.S

@@ -1,4 +1,5 @@
 #include <vm.h>
+#include <proc.h>
 
 .global entry
 entry:
@@ -67,35 +68,18 @@ interrupt_table_start:
 interrupt_table_end:
 
 syscall_entry:
-	stmfd r13!, {r1-r12, r14}
-
-	push {r0-r12, r14}
-
-	ldr r0, current_context_address
-	ldr r0, [r0]
-
-	push {r1}
-	mrs r1, spsr
-	str r1, [r0]
-	pop {r1}
-
-	add r0, #4
-	str r14, [r0]
+	SAVE_CONTEXT
 
-	add r0, #8
-	stmia r0, {r1-r14}^
-
-	pop {r0-r12, r14}
+	stmfd r13!, {r1-r12, r14}
 
 	bl handle_syscall
 
 	ldmfd r13!, {r1-r12, pc}^
 
-
-current_context_address: .word current_context
-
 irq_entry:
 	sub r14, r14, #4
+	SAVE_CONTEXT
+
 	stmfd r13!, {r0-r12, r14}
 
 	bl dispatch_interrupts