From: Matthias Kruk <m@m10k.eu>
Date: Thu, 14 Nov 2019 07:46:53 +0000 (+0900)
Subject: Add task_move_stack() function, which moves the current stack and updates ESP and EBP
X-Git-Url: https://git.corax.cc/?a=commitdiff_plain;h=8045d8888f5f5e47e5f2c2cb1c3523b6e539a12f;p=corax

Add task_move_stack() function, which moves the current stack and updates ESP and EBP
---

diff --git a/kernel/arch/task.S b/kernel/arch/task.S
index c7e5e32..1897a6d 100644
--- a/kernel/arch/task.S
+++ b/kernel/arch/task.S
@@ -29,6 +29,7 @@
 .global task_switch
 .global task_get_current
 .global task_set_current
+.global task_move_stack
 
 task_prepare:
 	/*
@@ -397,3 +398,89 @@ task_set_current:
 1:	movl	4(%esp), %ecx
 	movl	%ecx, OFFSET_CPU_CTASK(%eax)
 	ret
+
+task_move_stack:
+	/*
+	 * void task_move_stack(void *dst, void *src, u32_t size)
+	 *
+	 *  dst  =  4(%esp)
+	 *  src  =  8(%esp)
+	 *  size = 12(%esp)
+	 */
+
+	/*
+	 * For the sake of performance, don't copy the entire stack
+	 * but just the portion that was actually used, i.e. the
+	 * following:
+	 *
+	 * +-----+ <- src + size
+	 * |     |
+	 * |     |
+	 * +-----+ <- ESP
+	 * |     |
+	 * |     |
+	 * +-----+ <- src
+	 */
+
+	/* compute the offset into the new stack */
+	movl	%esp, %edi
+	subl	8(%esp), %edi /* ESP - src = offset  */
+	addl	4(%esp), %edi /* offset + dst = nESP */
+
+	/* put ESP into ESI so we can copy from ESI to EDI */
+	movl	%esp, %esi
+
+	/* calculate the upper limit for EDI and put it into EDX */
+	movl	4(%esp), %edx
+	addl	12(%esp), %edx
+
+	/*
+	 * Update the stack pointers now, since we won't need the
+	 * stack anymore afterwards. To update EBP, we need to subtract
+	 * the old base and add the new one, so do that before updating
+	 * ESP.
+	 */
+	subl	8(%esp), %ebp
+	addl	4(%esp), %ebp
+	movl	%edi, %esp
+
+	/*
+	 * To copy the stack, keep copying from %(esi) to (%edi),
+	 * increasing the two pointers, until %edi reaches %edx
+	*/
+
+0:	cmpl	%edx, %edi
+	jge		1f
+
+	movl	(%esi), %eax
+	movl	%eax, (%edi)
+	addl	$4, %esi
+	addl	$4, %edi
+	jmp		0b
+
+	/* iterate over the new stack, adjusting pointers */
+1:	movl	%esp, %edi
+	movl	%edx, %esi
+	movl	8(%esp), %ecx /* lower bound */
+	movl	%ecx, %edx
+	addl	12(%esp), %edx /* upper bound */
+
+2:	cmpl	%esi, %edi
+	jge		4f
+
+	movl	(%edi), %eax
+	cmpl	%ecx, %eax
+	jl		3f
+	cmpl	%edx, %eax
+	jge		3f
+
+	/* adjust the pointer */
+	subl	%ecx, %eax
+	addl	4(%esp), %eax
+	/* store it on the stack */
+	movl	%eax, (%edi)
+3:	addl	$4, %edi
+	jmp		2b
+
+	/* Stacks have been copied and stack pointers updated. We're done. */
+4:	ret
diff --git a/kernel/include/arch.h b/kernel/include/arch.h
index 10536e5..ed9b2b9 100644
--- a/kernel/include/arch.h
+++ b/kernel/include/arch.h
@@ -82,6 +82,7 @@ int     task_switch(struct task*);
 
 task_t* task_get_current(void);
 void    task_set_current(task_t*);
+void    task_move_stack(void*, void*, u32_t);
 
 /*
  * Definitions, types, and prototypes related to paging