X-Git-Url: https://pintos-os.org/cgi-bin/gitweb.cgi?a=blobdiff_plain;f=src%2Fthreads%2Fswitch.S;h=4f0d412c7266e3117d6fa33bdb2e9f598dbb63e8;hb=7d4e3dda080a47db88616f1c0d975f2091be47f1;hp=a7c27fb03eb8fc3cb73ccee19f07ef21438d61ea;hpb=750d21936d284127e265d050ccbce76fca1ece1a;p=pintos-anon

diff --git a/src/threads/switch.S b/src/threads/switch.S
index a7c27fb..4f0d412 100644
--- a/src/threads/switch.S
+++ b/src/threads/switch.S
@@ -1,36 +1,65 @@
-#### 0(%esp) - old registers
-#### 16(%esp) - return address
-#### 20(%esp) - current thread
-#### 24(%esp) - new thread
+#include "threads/switch.h"
 
-        .globl thread_switch 
-thread_switch:
+#### struct thread *switch_threads (struct thread *cur, struct thread *next);
+####
+#### Switches from CUR, which must be the running thread, to NEXT,
+#### which must also be running switch_threads(), returning CUR in
+#### NEXT's context.
+####
+#### This function works by assuming that the thread we're switching
+#### into is also running switch_threads().  Thus, all it has to do is
+#### preserve a few registers on the stack, then switch stacks and
+#### restore the registers.  As part of switching stacks we record the
+#### current stack pointer in CUR's thread structure.
+
+	.intel_syntax noprefix
+
+.globl switch_threads 
+switch_threads:
 	# Save caller's register state.
-	# Note that the SVR4 ABI allows us to destroy %eax, %ecx, %edx.
+	#
+	# Note that the SVR4 ABI allows us to destroy eax, ecx, edx,
+	# but requires us to preserve ebx, ebp, esi, edi.  See
+	# [SysV-ABI-386] pages 3-11 and 3-12 for details.
+	#
 	# This stack frame must match the one set up by thread_create().
-	pushl %ebx
-	pushl %ebp
-	pushl %esi
-	pushl %edi
+	push ebx
+	push ebp
+	push esi
+	push edi
 
 	# Get offsetof (struct thread, stack).
-	.globl thread_stack_ofs
-	mov thread_stack_ofs, %edx
+.globl thread_stack_ofs
+	mov edx, thread_stack_ofs
 
 	# Save current stack pointer to old thread's stack, if any.
-	movl 20(%esp), %eax
-	test %eax, %eax
+	mov eax, SWITCH_CUR[esp]
+	test eax, eax
 	jz 1f
-	movl %esp, (%eax,%edx,1)
+	mov [eax + edx], esp
 1:
 
 	# Restore stack pointer from new thread's stack.
-	movl 24(%esp), %ecx
-	movl (%ecx,%edx,1), %esp
+	mov ecx, SWITCH_NEXT[esp]
+	mov esp, [ecx + edx]
 
 	# Restore caller's register state.
-	popl %edi
-	popl %esi
-	popl %ebp
-	popl %ebx
+	pop edi
+	pop esi
+	pop ebp
+	pop ebx
         ret
+
+.globl switch_entry
+switch_entry:
+	# Discard switch_threads() arguments.
+	add esp, 8
+
+	# Call schedule_tail(prev).
+	push eax
+.globl schedule_tail
+	call schedule_tail
+	add esp, 4
+
+	# Start thread proper.
+	ret