-#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
+.func 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
+ 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
+.endfunc
.globl switch_entry
+.func switch_entry
switch_entry:
# Discard switch_threads() arguments.
- addl $8, %esp
+ add esp, 8
# Call schedule_tail(prev).
- pushl %eax
+ push eax
.globl schedule_tail
call schedule_tail
- addl $4, %esp
+ add esp, 4
# Start thread proper.
ret
+.endfunc