X-Git-Url: https://pintos-os.org/cgi-bin/gitweb.cgi?a=blobdiff_plain;f=src%2Fthreads%2Fswitch.S;h=4f0d412c7266e3117d6fa33bdb2e9f598dbb63e8;hb=af584a2aaa0ed870dc76df97097dbee32aeac488;hp=fddd821afc8ef296fb22d800768e743577be89c5;hpb=44d0fa6a2b24a84e5eb0d54959ed91c1d4f15343;p=pintos-anon

diff --git a/src/threads/switch.S b/src/threads/switch.S
index fddd821..4f0d412 100644
--- a/src/threads/switch.S
+++ b/src/threads/switch.S
@@ -1,47 +1,65 @@
-#include "switch.h"
+#include "threads/switch.h"
 
-        .globl switch_threads 
+#### 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 SWITCH_CUR(%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 SWITCH_NEXT(%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
+.globl switch_entry
 switch_entry:
-	# Discard thread_switch() arguments.
-	addl $8, %esp
+	# Discard switch_threads() arguments.
+	add esp, 8
 
 	# Call schedule_tail(prev).
-	pushl %eax
-	.globl schedule_tail
+	push eax
+.globl schedule_tail
 	call schedule_tail
-	addl $4, %esp
+	add esp, 4
 
 	# Start thread proper.
 	ret