#include "threads/switch.h" #### 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, # 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(). push ebx push ebp push esi push edi # Get offsetof (struct thread, stack). .globl thread_stack_ofs mov edx, thread_stack_ofs # Save current stack pointer to old thread's stack, if any. mov eax, SWITCH_CUR[esp] test eax, eax jz 1f mov [eax + edx], esp 1: # Restore stack pointer from new thread's stack. mov ecx, SWITCH_NEXT[esp] mov esp, [ecx + edx] # Restore caller's register state. pop edi pop esi pop ebp pop ebx ret .endfunc .globl switch_entry .func 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 .endfunc