1 #include "threads/switch.h"
3 #### struct thread *switch_threads (struct thread *cur, struct thread *next);
5 #### Switches from CUR, which must be the running thread, to NEXT,
6 #### which must also be running switch_threads(), returning CUR in
9 #### This function works by assuming that the thread we're switching
10 #### into is also running switch_threads(). Thus, all it has to do is
11 #### preserve a few registers on the stack, then switch stacks and
12 #### restore the registers. As part of switching stacks we record the
13 #### current stack pointer in CUR's thread structure.
17 # Save caller's register state.
19 # Note that the SVR4 ABI allows us to destroy %eax, %ecx, %edx,
20 # but requires us to preserve %ebx, %ebp, %esi, %edi. See
21 # [SysV-ABI-386] pages 3-11 and 3-12 for details.
23 # This stack frame must match the one set up by thread_create().
29 # Get offsetof (struct thread, stack).
30 .globl thread_stack_ofs
31 mov thread_stack_ofs, %edx
33 # Save current stack pointer to old thread's stack, if any.
34 movl SWITCH_CUR(%esp), %eax
37 movl %esp, (%eax,%edx,1)
40 # Restore stack pointer from new thread's stack.
41 movl SWITCH_NEXT(%esp), %ecx
42 movl (%ecx,%edx,1), %esp
44 # Restore caller's register state.
53 # Discard switch_threads() arguments.
56 # Call schedule_tail(prev).
62 # Start thread proper.