minix/servers/vm/break.c

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/* 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
*/
#define _SYSTEM 1
#include <minix/callnr.h>
#include <minix/com.h>
#include <minix/config.h>
#include <minix/const.h>
#include <minix/ds.h>
#include <minix/endpoint.h>
#include <minix/keymap.h>
#include <minix/minlib.h>
#include <minix/type.h>
#include <minix/ipc.h>
#include <minix/sysutil.h>
#include <minix/syslib.h>
#include <errno.h>
#include <env.h>
#include "glo.h"
#include "vm.h"
#include "proto.h"
#include "util.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(message *msg)
{
/* Perform the brk(addr) system call.
* The parameter, 'addr' is the new virtual address in D space.
*/
int proc;
if(vm_isokendpt(msg->VMB_ENDPOINT, &proc) != OK) {
printf("VM: bogus endpoint VM_BRK %d\n", msg->VMB_ENDPOINT);
return EINVAL;
}
return real_brk(&vmproc[proc], (vir_bytes) msg->VMB_ADDR);
}
/*===========================================================================*
* adjust *
*===========================================================================*/
PUBLIC int adjust(rmp, data_clicks, sp)
struct vmproc *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, sp_lower, old_clicks;
int changed, r;
long base_of_stack, sp_delta; /* longs avoid certain problems */
mem_dp = &rmp->vm_arch.vm_seg[D]; /* pointer to data segment map */
mem_sp = &rmp->vm_arch.vm_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. */
sp_delta = (long) mem_sp->mem_vir - (long) sp_click;
sp_lower = (sp_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 (sp_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 (sp_delta > 0) {
mem_sp->mem_vir -= sp_delta;
mem_sp->mem_phys -= sp_delta;
mem_sp->mem_len += sp_delta;
changed |= STACK_CHANGED;
}
/* Do the new data and stack segment sizes fit in the address space? */
r = (rmp->vm_arch.vm_seg[D].mem_vir + rmp->vm_arch.vm_seg[D].mem_len >
rmp->vm_arch.vm_seg[S].mem_vir) ? ENOMEM : OK;
if(r == OK && (rmp->vm_flags & VMF_HASPT) &&
rmp->vm_endpoint != VM_PROC_NR) {
vm_assert(rmp->vm_heap);
if(old_clicks < data_clicks) {
vir_bytes more;
more = (data_clicks - old_clicks) << CLICK_SHIFT;
if(map_region_extend(rmp, rmp->vm_heap, more) != OK) {
printf("VM: brk: map_region_extend failed\n");
return ENOMEM;
}
} else if(old_clicks > data_clicks) {
vir_bytes less;
less = (old_clicks - data_clicks) << CLICK_SHIFT;
if(map_region_shrink(rmp->vm_heap, less) != OK) {
printf("VM: brk: map_region_shrink failed\n");
return ENOMEM;
}
}
}
if (r == OK)
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 += sp_delta;
mem_sp->mem_phys += sp_delta;
mem_sp->mem_len -= sp_delta;
}
return(ENOMEM);
}
/*===========================================================================*
* real_brk *
*===========================================================================*/
PUBLIC int real_brk(vmp, v)
struct vmproc *vmp;
vir_bytes v;
{
vir_bytes new_sp;
vir_clicks new_clicks;
int r;
new_clicks = (vir_clicks) ( ((long) v + CLICK_SIZE - 1) >> CLICK_SHIFT);
if (new_clicks < vmp->vm_arch.vm_seg[D].mem_vir) {
printf("VM: real_brk failed because new_clicks too high: %d\n",
new_clicks);
return(ENOMEM);
}
new_clicks -= vmp->vm_arch.vm_seg[D].mem_vir;
if ((r=get_stack_ptr(vmp->vm_endpoint, &new_sp)) != OK)
vm_panic("couldn't get stack pointer", r);
r = adjust(vmp, new_clicks, new_sp);
return r;
}