minix/lib/libc/arch/i386/misc/ucontext.S

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#include <machine/asm.h>
#ifdef __ACK__
.text
begtext:
#ifdef __ACK__
.rom
#else
.data
#endif
begrom:
.data
begdata:
.bss
begbss:
#endif
IMPORT(getuctx)
IMPORT(setuctx)
IMPORT(resumecontext)
/* Offsets into ucontext_t structure. Keep in sync with <sys/ucontext.h>! */
#define UC_FLAGS 0
#define UC_LINK UC_FLAGS + 4
#define MCTX UC_LINK + 4
#define MAGIC MCTX
#define GS MAGIC+4
#define FS GS+2
#define ES FS+2
#define DS ES+2
#define DI DS+2
#define SI DI+4
#define BP SI+4
#define ST BP+4 /* Hole for another SP */
#define BX ST+4
#define DX BX+4
#define CX DX+4
#define AX CX+4
#define RETADR AX+4
#define PC RETADR+4
#define CS PC+4
#define PSW CS+4
#define SP PSW+4
#define SS SP+4
/* MCF_MAGIC value from <mcontext.h> */
#define MCF_MAGIC 0xc0ffee
/* Values from <sys/ucontext.h> */
#define UCF_IGNFPU 0x002
#define UCF_IGNSIGM 0x004
/* EINVAL from errno.h */
#define EFAULT 14
#define EINVAL 22
/* int getcontext(ucontext_t *ucp)
* Initialise the structure pointed to by ucp to the current user context
* of the calling thread. */
ENTRY(getcontext)
/* In case a process does not use the FPU and is neither interested in
* saving its signal mask, then we can skip the context switch to
* PM and kernel altogether and only save general-purpose registers. */
mov (%esp), %ecx /* Save return address:
* When setcontext or swapcontext is called,
* we jump to this address and continue
* running. */
mov 4(%esp), %edx /* edx = ucp */
/* Check null pointer */
cmp $0, %edx /* edx == NULL? */
jne 3f /* Not null, continue */
movl $EFAULT, (_C_LABEL(errno))
xor %eax, %eax
dec %eax /* return -1 */
ret
3: /* Check flags */
push %ecx /* save ecx */
push %ebx /* save ebx */
lea UC_FLAGS(%edx), %ebx /* ebx = &(ucp->uc_flags) */
mov (%ebx), %ecx /* ecx = ucp->uc_flags */
mov $UCF_IGNFPU, %eax
or $UCF_IGNSIGM, %eax
cmp %eax, %ecx /* is UCF_IGNFPU or UCF_IGNSIGM set? */
pop %ebx /* restore ebx */
pop %ecx /* restore ecx */
jz 1f /* Both are set, skip getuctx */
0:
push %ecx /* Save ecx */
push %edx
call _C_LABEL(getuctx) /* getuctx(ucp) */
pop %edx /* clean up stack and restore edx */
pop %ecx /* Restore ecx */
1:
/* Save the context */
mov 4(%esp), %edx /* edx = ucp */
pop %eax /* retaddr */
mov %eax, PC(%edx) /* Save real RTA in mcp struct */
mov %esp, SP(%edx) /* Save stack pointer (now pointing to ucp) */
/* Save GP registers */
mov %ebp, BP(%edx) /* Save EBP */
mov %esi, SI(%edx) /* Save ESI */
mov %edi, DI(%edx) /* Save EDI */
mov %ebx, BX(%edx) /* Save EBX */
mov %ecx, CX(%edx) /* Save ECX */
movl $MCF_MAGIC, MAGIC(%edx) /* Set magic value */
push %eax /* Restore retaddr */
xor %eax, %eax /* Return 0 */
2:
add $4, %esp /* Remove stale (setcontext) RTA */
jmp *%ecx /* Restore return address */
/* int setcontext(const ucontext_t *ucp)
* Restore the user context pointed to by ucp. A successful call to
* setcontext does not return; program execution resumes at the point
* specified by the ucp argument. If ucp was created with getcontext(),
* program execution continues as if the corresponding call of getcontext()
* had just returned. If ucp was created with makecontext(), program
* execution continues with the function passed to makecontext(). */
ENTRY(setcontext)
/* In case a process does not use the FPU and is neither interested in
* restoring its signal mask, then we can skip the context switch to
* PM and kernel altogether and restore state here. */
mov 4(%esp), %edx /* edx = ucp */
/* Check null pointer */
cmp $0, %edx /* edx == NULL? */
jnz 3f /* Not null, continue */
movl $EFAULT, (_C_LABEL(errno))
xor %eax, %eax
dec %eax /* return -1 */
ret
3: /* Check flags */
push %ebx /* save ebx */
lea MAGIC(%edx), %ebx /* ebx = &(ucp->mc_context.mc_magic) */
mov (%ebx), %ecx /* ecx = ucp->mc_context.mc_magic */
pop %ebx /* restore ebx */
cmp $MCF_MAGIC, %ecx /* is the magic value set (is context valid)?*/
jz 4f /* is set, proceed */
movl $EINVAL, (_C_LABEL(errno)) /* not set, return error code */
xor %eax, %eax
dec %eax /* return -1 */
ret
4: push %ebx /* save ebx */
lea UC_FLAGS(%edx), %ebx /* ebx = &(ucp->uc_flags) */
mov (%ebx), %ecx /* ecx = ucp->uc_flags */
pop %ebx /* restore ebx */
mov $UCF_IGNFPU, %eax
or $UCF_IGNSIGM, %eax
cmp %eax, %ecx /* Are UCF_IGNFPU and UCF_IGNSIGM flags set? */
jz 1f /* Both are set, so don't bother restoring FPU
* state and signal mask */
0: push %ecx /* Save ecx */
push %edx
call _C_LABEL(setuctx) /* setuctx(ucp) */
pop %edx /* Clean up stack and restore edx */
pop %ecx /* Restore ecx */
1: /* Restore the registers */
mov 4(%esp), %edx /* edx = ucp */
mov CX(%edx), %ecx /* Restore ECX */
mov BX(%edx), %ebx /* Restore EBX */
mov DI(%edx), %edi /* Restore EDI */
mov SI(%edx), %esi /* Restore ESI */
mov BP(%edx), %ebp /* Restore EBP */
mov SP(%edx), %esp /* Restore stack pointer */
2:
jmp *PC(%edx) /* Push RTA onto stack so we can return to it */
/* void ctx_start((void *func)(int arg1, ..., argn), arg1, ..., argn,
* ucontext_t *ucp)
* A wrapper to start function `func'. ESI register will contain a pointer
* to ucp on the stack. By setting ESP to ESI, we effectively 'remove' all
* arguments to `func' from the stack. Finally, a call to resumecontext
* will start the next context in the linked list (or exit the program if
* there is no context). */
ENTRY(ctx_start)
/* 0(esp) -> func
* 4(esp) -> arg1
* ...
* 4*n(esp) -> argn
* 4*(n+1)(esp) -> ucp */
pop %eax /* eax = func */
call *%eax /* func(arg1, ..., argn) */
mov %esi, %esp /* Clean up stack */
/* ucp is now at the top of the stack again */
call _C_LABEL(resumecontext) /* resumecontext(ucp) */
ret /* never reached */