minix/kernel/system/do_fork.c
David van Moolenbroek c2aef85eda Clear trace bit for child on fork.
Without this, a forking single-stepped process will have its child
die from a TRAP signal right away.
2009-05-13 21:58:10 +00:00

95 lines
3.1 KiB
C

/* The kernel call implemented in this file:
* m_type: SYS_FORK
*
* The parameters for this kernel call are:
* m1_i1: PR_SLOT (child's process table slot)
* m1_i2: PR_ENDPT (parent, process that forked)
*/
#include "../system.h"
#include <signal.h>
#include <minix/endpoint.h>
#if USE_FORK
/*===========================================================================*
* do_fork *
*===========================================================================*/
PUBLIC int do_fork(m_ptr)
register message *m_ptr; /* pointer to request message */
{
/* Handle sys_fork(). PR_ENDPT has forked. The child is PR_SLOT. */
#if (_MINIX_CHIP == _CHIP_INTEL)
reg_t old_ldt_sel;
#endif
register struct proc *rpc; /* child process pointer */
struct proc *rpp; /* parent process pointer */
struct mem_map *map_ptr; /* virtual address of map inside caller (PM) */
int i, gen, r;
int p_proc;
if(!isokendpt(m_ptr->PR_ENDPT, &p_proc))
return EINVAL;
rpp = proc_addr(p_proc);
rpc = proc_addr(m_ptr->PR_SLOT);
if (isemptyp(rpp) || ! isemptyp(rpc)) return(EINVAL);
map_ptr= (struct mem_map *) m_ptr->PR_MEM_PTR;
/* Copy parent 'proc' struct to child. And reinitialize some fields. */
gen = _ENDPOINT_G(rpc->p_endpoint);
#if (_MINIX_CHIP == _CHIP_INTEL)
old_ldt_sel = rpc->p_seg.p_ldt_sel; /* backup local descriptors */
#endif
*rpc = *rpp; /* copy 'proc' struct */
#if (_MINIX_CHIP == _CHIP_INTEL)
rpc->p_seg.p_ldt_sel = old_ldt_sel; /* restore descriptors */
#endif
if(++gen >= _ENDPOINT_MAX_GENERATION) /* increase generation */
gen = 1; /* generation number wraparound */
rpc->p_nr = m_ptr->PR_SLOT; /* this was obliterated by copy */
rpc->p_endpoint = _ENDPOINT(gen, rpc->p_nr); /* new endpoint of slot */
rpc->p_reg.retreg = 0; /* child sees pid = 0 to know it is child */
rpc->p_user_time = 0; /* set all the accounting times to 0 */
rpc->p_sys_time = 0;
rpc->p_reg.psw &= ~TRACEBIT; /* clear trace bit */
/* Parent and child have to share the quantum that the forked process had,
* so that queued processes do not have to wait longer because of the fork.
* If the time left is odd, the child gets an extra tick.
*/
rpc->p_ticks_left = (rpc->p_ticks_left + 1) / 2;
rpp->p_ticks_left = rpp->p_ticks_left / 2;
/* If the parent is a privileged process, take away the privileges from the
* child process and inhibit it from running by setting the NO_PRIV flag.
* The caller should explicitely set the new privileges before executing.
*/
if (priv(rpp)->s_flags & SYS_PROC) {
rpc->p_priv = priv_addr(USER_PRIV_ID);
rpc->p_rts_flags |= NO_PRIV;
}
/* Calculate endpoint identifier, so caller knows what it is. */
m_ptr->PR_ENDPT = rpc->p_endpoint;
/* Install new map */
r = newmap(rpc, map_ptr);
/* Don't schedule process in VM mode until it has a new pagetable. */
if(m_ptr->PR_FORK_FLAGS & PFF_VMINHIBIT) {
RTS_LOCK_SET(rpc, VMINHIBIT);
}
/* Only one in group should have SIGNALED, child doesn't inherit tracing. */
RTS_LOCK_UNSET(rpc, (SIGNALED | SIG_PENDING | P_STOP));
sigemptyset(&rpc->p_pending);
return r;
}
#endif /* USE_FORK */