/*
* Functions for entering user mode.
*
* This should not be used by threads returning from traps - they
* should just return from mips_trap(). It should be used by threads
* entering user mode for the first time - whether the child thread in
* a fork(), or into a brand-new address space after exec(), or when
* starting the first userlevel program.
*
* mips_usermode is the common code. It should not be called outside
* the mips port.
*
* md_usermode is meant for use in exec and equivalent.
* md_forkentry, in syscall.c, is meant for use in fork.
*/
void
mips_usermode(struct trapframe *tf)
{
/*
* Interrupts should be off within the kernel while entering
* usermode. However, while in usermode, interrupts should be
* on. To interact properly with the spl-handling logic above,
* we call splhigh() to disable interrupts, but set curspl
* explicitly to 0.
*/
splhigh();
curspl = 0;
/*
* This assertion will fail if either
* (1) curkstack is corrupted, or
* (2) the trap frame is not on our own kernel stack.
*
* If curkstack is corrupted, the next trap back to the kernel
* will (most likely) hang the system, so it's better to find
* out now.
*
* It's necessary for the trap frame used here to be on the
* current thread's own stack. It cannot correctly be on either
* another thread's stack or in the kernel heap. (Why?)
*/
assert(SAME_STACK(curkstack-1, (vaddr_t)tf));
/*
* This actually does it. See exception.S.
*/
asm_usermode(tf);
}
/*
* Functions for entering user mode.
*
* This should not be used by threads returning from traps - they
* should just return from mips_trap(). It should be used by threads
* entering user mode for the first time - whether the child thread in
* a fork(), or into a brand-new address space after exec(), or when
* starting the first userlevel program.
*
* mips_usermode is the common code. It should not be called outside
* the mips port.
*
* md_usermode is meant for use in exec and equivalent.
* md_forkentry, in syscall.c, is meant for use in fork.
*/
void
mips_usermode(struct trapframe *tf)
{
/*
* Interrupts should be off within the kernel while entering
* usermode. However, while in usermode, interrupts should be
* on. To interact properly with the spl-handling logic above,
* we call splhigh() to disable interrupts, but set curspl
* explicitly to 0.
*/
splhigh();
curspl = 0;
/*
* If curkstack is wrong, chances are the first trap back to
* the kernel will hang the system. So make sure it's something
* near correct.
*
* This test assumes that tf is on our own thread stack, but
* that's more or less necessary anyway.
*/
assert(((curkstack-1) & 0xffffe000)==(((u_int32_t)tf) & 0xffffe000));
/*
* This actually does it. See exception.S.
*/
asm_usermode(tf);
}
/*
* Function for entering user mode.
*
* This should not be used by threads returning from traps - they
* should just return from mips_trap(). It should be used by threads
* entering user mode for the first time - whether the child thread in
* a fork(), or into a brand-new address space after exec(), or when
* starting the first userlevel program.
*
* It works by jumping into the exception return code.
*
* mips_usermode is common code for this. It cannot usefully be called
* outside the mips port, but should be called from one of the
* following places:
* - enter_new_process, for use by exec and equivalent.
* - enter_forked_process, in syscall.c, for use by fork.
*/
void
mips_usermode(struct trapframe *tf)
{
/*
* Interrupts should be off within the kernel while entering
* user mode. However, while in user mode, interrupts should
* be on. To interact properly with the spl-handling logic
* above, we explicitly call spl0() and then call cpu_irqoff().
*/
spl0();
cpu_irqoff();
cputhreads[curcpu->c_number] = (vaddr_t)curthread;
cpustacks[curcpu->c_number] = (vaddr_t)curthread->t_stack + STACK_SIZE;
/*
* This assertion will fail if either
* (1) cpustacks[] is corrupted, or
* (2) the trap frame is not on our own kernel stack, or
* (3) the boot thread tries to enter user mode.
*
* If cpustacks[] is corrupted, the next trap back to the
* kernel will (most likely) hang the system, so it's better
* to find out now.
*
* It's necessary for the trap frame used here to be on the
* current thread's own stack. It cannot correctly be on
* either another thread's stack or in the kernel heap.
* (Exercise: why?)
*/
KASSERT(((vaddr_t)tf) >= ((vaddr_t)curthread->t_stack));
KASSERT(((vaddr_t)tf) < ((vaddr_t)curthread->t_stack+STACK_SIZE));
//KASSERT(SAME_STACK(cpustacks[curcpu->c_number]-1, (vaddr_t)tf));
/*
* This actually does it. See exception.S.
*/
asm_usermode(tf);
}
