src/arch/x86/thread.c

   1 /* SPDX-License-Identifier: GPL-2.0-only */
   2
   3 #include <thread.h>
   4
   5 #if ENV_X86_64
   6 #error COOP_MULTITASKING does not currently support x86_64
   7 #endif
   8
   9 /* The stack frame looks like the following after a pushad instruction. */
  10 struct pushad_regs {
  11         uint32_t edi; /* Offset 0x00 */
  12         uint32_t esi; /* Offset 0x04 */
  13         uint32_t ebp; /* Offset 0x08 */
  14         uint32_t esp; /* Offset 0x0c */
  15         uint32_t ebx; /* Offset 0x10 */
  16         uint32_t edx; /* Offset 0x14 */
  17         uint32_t ecx; /* Offset 0x18 */
  18         uint32_t eax; /* Offset 0x1c */
  19 };
  20
  21 static inline uintptr_t push_stack(uintptr_t cur_stack, uintptr_t value)
  22 {
  23         uintptr_t *addr;
  24
  25         cur_stack -= sizeof(value);
  26         addr = (uintptr_t *)cur_stack;
  27         *addr = value;
  28         return cur_stack;
  29 }
  30
  31 void arch_prepare_thread(struct thread *t,
  32                         asmlinkage void (*thread_entry)(void *), void *arg)
  33 {
  34         uintptr_t stack = t->stack_current;
  35
  36         /* Imitate thread_entry(t) with return address of 0. thread_entry()
  37          * is assumed to never return. */
  38         stack = push_stack(stack, (uintptr_t)arg);
  39         stack = push_stack(stack, (uintptr_t)0);
  40         stack = push_stack(stack, (uintptr_t)thread_entry);
  41         /* Make room for the registers. Ignore initial values. */
  42         stack -= sizeof(struct pushad_regs);
  43
  44         t->stack_current = stack;
  45 }