X-Git-Url: https://pintos-os.org/cgi-bin/gitweb.cgi?a=blobdiff_plain;f=src%2Fthreads%2Fswitch.S;h=5bb56b55ec1a84de04295b39f23032bd1ae94e2b;hb=24445a35e861ddb50df05731ca4635fbd36e04a4;hp=b00823af50044cd4e2cfb0a1f73fbd5802d18fd5;hpb=987024569c1e5e9468238849dd79ec8d386352e6;p=pintos-anon

diff --git a/src/threads/switch.S b/src/threads/switch.S
index b00823a..5bb56b5 100644
--- a/src/threads/switch.S
+++ b/src/threads/switch.S
@@ -1,9 +1,25 @@
-#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 thread_switch(), 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.
+
+.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
+	# [SV-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
@@ -11,7 +27,7 @@ switch_threads:
 	pushl %edi
 
 	# Get offsetof (struct thread, stack).
-	.globl thread_stack_ofs
+.globl thread_stack_ofs
 	mov thread_stack_ofs, %edx
 
 	# Save current stack pointer to old thread's stack, if any.
@@ -32,7 +48,16 @@ switch_threads:
 	popl %ebx
         ret
 
-	.globl switch_thunk
-switch_thunk:
+.globl switch_entry
+switch_entry:
+	# Discard switch_threads() arguments.
 	addl $8, %esp
+
+	# Call schedule_tail(prev).
+	pushl %eax
+.globl schedule_tail
+	call schedule_tail
+	addl $4, %esp
+
+	# Start thread proper.
 	ret