minix/servers/pm/break.c
2006-05-11 14:57:23 +00:00

181 lines
6.7 KiB
C

/* The MINIX model of memory allocation reserves a fixed amount of memory for
* the combined text, data, and stack segments. The amount used for a child
* process created by FORK is the same as the parent had. If the child does
* an EXEC later, the new size is taken from the header of the file EXEC'ed.
*
* The layout in memory consists of the text segment, followed by the data
* segment, followed by a gap (unused memory), followed by the stack segment.
* The data segment grows upward and the stack grows downward, so each can
* take memory from the gap. If they meet, the process must be killed. The
* procedures in this file deal with the growth of the data and stack segments.
*
* The entry points into this file are:
* do_brk: BRK/SBRK system calls to grow or shrink the data segment
* adjust: see if a proposed segment adjustment is allowed
* size_ok: see if the segment sizes are feasible (i86 only)
*/
#include "pm.h"
#include <signal.h>
#include "mproc.h"
#include "param.h"
#define DATA_CHANGED 1 /* flag value when data segment size changed */
#define STACK_CHANGED 2 /* flag value when stack size changed */
/*===========================================================================*
* do_brk *
*===========================================================================*/
PUBLIC int do_brk()
{
/* Perform the brk(addr) system call.
*
* The call is complicated by the fact that on some machines (e.g., 8088),
* the stack pointer can grow beyond the base of the stack segment without
* anybody noticing it.
* The parameter, 'addr' is the new virtual address in D space.
*/
register struct mproc *rmp;
int r;
vir_bytes v, new_sp;
vir_clicks new_clicks;
rmp = mp;
v = (vir_bytes) m_in.addr;
new_clicks = (vir_clicks) ( ((long) v + CLICK_SIZE - 1) >> CLICK_SHIFT);
if (new_clicks < rmp->mp_seg[D].mem_vir) {
rmp->mp_reply.reply_ptr = (char *) -1;
return(ENOMEM);
}
new_clicks -= rmp->mp_seg[D].mem_vir;
if ((r=get_stack_ptr(who_e, &new_sp)) != OK) /* ask kernel for sp value */
panic(__FILE__,"couldn't get stack pointer", r);
r = adjust(rmp, new_clicks, new_sp);
rmp->mp_reply.reply_ptr = (r == OK ? m_in.addr : (char *) -1);
return(r); /* return new address or -1 */
}
/*===========================================================================*
* adjust *
*===========================================================================*/
PUBLIC int adjust(rmp, data_clicks, sp)
register struct mproc *rmp; /* whose memory is being adjusted? */
vir_clicks data_clicks; /* how big is data segment to become? */
vir_bytes sp; /* new value of sp */
{
/* See if data and stack segments can coexist, adjusting them if need be.
* Memory is never allocated or freed. Instead it is added or removed from the
* gap between data segment and stack segment. If the gap size becomes
* negative, the adjustment of data or stack fails and ENOMEM is returned.
*/
register struct mem_map *mem_sp, *mem_dp;
vir_clicks sp_click, gap_base, lower, old_clicks;
int changed, r, ft;
long base_of_stack, delta; /* longs avoid certain problems */
mem_dp = &rmp->mp_seg[D]; /* pointer to data segment map */
mem_sp = &rmp->mp_seg[S]; /* pointer to stack segment map */
changed = 0; /* set when either segment changed */
/* See if stack size has gone negative (i.e., sp too close to 0xFFFF...) */
base_of_stack = (long) mem_sp->mem_vir + (long) mem_sp->mem_len;
sp_click = sp >> CLICK_SHIFT; /* click containing sp */
if (sp_click >= base_of_stack)
{
return(ENOMEM); /* sp too high */
}
/* Compute size of gap between stack and data segments. */
delta = (long) mem_sp->mem_vir - (long) sp_click;
lower = (delta > 0 ? sp_click : mem_sp->mem_vir);
/* Add a safety margin for future stack growth. Impossible to do right. */
#define SAFETY_BYTES (384 * sizeof(char *))
#define SAFETY_CLICKS ((SAFETY_BYTES + CLICK_SIZE - 1) / CLICK_SIZE)
gap_base = mem_dp->mem_vir + data_clicks + SAFETY_CLICKS;
if (lower < gap_base)
{
return(ENOMEM); /* data and stack collided */
}
/* Update data length (but not data orgin) on behalf of brk() system call. */
old_clicks = mem_dp->mem_len;
if (data_clicks != mem_dp->mem_len) {
mem_dp->mem_len = data_clicks;
changed |= DATA_CHANGED;
}
/* Update stack length and origin due to change in stack pointer. */
if (delta > 0) {
mem_sp->mem_vir -= delta;
mem_sp->mem_phys -= delta;
mem_sp->mem_len += delta;
changed |= STACK_CHANGED;
}
/* Do the new data and stack segment sizes fit in the address space? */
ft = (rmp->mp_flags & SEPARATE);
#if (CHIP == INTEL && _WORD_SIZE == 2)
r = size_ok(ft, rmp->mp_seg[T].mem_len, rmp->mp_seg[D].mem_len,
rmp->mp_seg[S].mem_len, rmp->mp_seg[D].mem_vir, rmp->mp_seg[S].mem_vir);
#else
r = (rmp->mp_seg[D].mem_vir + rmp->mp_seg[D].mem_len >
rmp->mp_seg[S].mem_vir) ? ENOMEM : OK;
#endif
if (r == OK) {
int r2;
if (changed && (r2=sys_newmap(rmp->mp_endpoint, rmp->mp_seg)) != OK)
panic(__FILE__,"couldn't sys_newmap in adjust", r2);
return(OK);
}
/* New sizes don't fit or require too many page/segment registers. Restore.*/
if (changed & DATA_CHANGED) mem_dp->mem_len = old_clicks;
if (changed & STACK_CHANGED) {
mem_sp->mem_vir += delta;
mem_sp->mem_phys += delta;
mem_sp->mem_len -= delta;
}
return(ENOMEM);
}
#if (CHIP == INTEL && _WORD_SIZE == 2)
/*===========================================================================*
* size_ok *
*===========================================================================*/
PUBLIC int size_ok(file_type, tc, dc, sc, dvir, s_vir)
int file_type; /* SEPARATE or 0 */
vir_clicks tc; /* text size in clicks */
vir_clicks dc; /* data size in clicks */
vir_clicks sc; /* stack size in clicks */
vir_clicks dvir; /* virtual address for start of data seg */
vir_clicks s_vir; /* virtual address for start of stack seg */
{
/* Check to see if the sizes are feasible and enough segmentation registers
* exist. On a machine with eight 8K pages, text, data, stack sizes of
* (32K, 16K, 16K) will fit, but (33K, 17K, 13K) will not, even though the
* former is bigger (64K) than the latter (63K). Even on the 8088 this test
* is needed, since the data and stack may not exceed 4096 clicks.
* Note this is not used for 32-bit Intel Minix, the test is done in-line.
*/
int pt, pd, ps; /* segment sizes in pages */
pt = ( (tc << CLICK_SHIFT) + PAGE_SIZE - 1)/PAGE_SIZE;
pd = ( (dc << CLICK_SHIFT) + PAGE_SIZE - 1)/PAGE_SIZE;
ps = ( (sc << CLICK_SHIFT) + PAGE_SIZE - 1)/PAGE_SIZE;
if (file_type == SEPARATE) {
if (pt > MAX_PAGES || pd + ps > MAX_PAGES) return(ENOMEM);
} else {
if (pt + pd + ps > MAX_PAGES) return(ENOMEM);
}
if (dvir + dc > s_vir) return(ENOMEM);
return(OK);
}
#endif