swapcontext, and makecontext). - Fix VM to not erroneously think the stack segment and data segment have collided when a user-space thread invokes brk(). - Add test51 to test ucontext functionality. - Add man pages for ucontext system calls.
185 lines
6.4 KiB
C
185 lines
6.4 KiB
C
/* The MINIX model of memory allocation reserves a fixed amount of memory for
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* the combined text, data, and stack segments. The amount used for a child
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* process created by FORK is the same as the parent had. If the child does
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* an EXEC later, the new size is taken from the header of the file EXEC'ed.
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*
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* The layout in memory consists of the text segment, followed by the data
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* segment, followed by a gap (unused memory), followed by the stack segment.
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* The data segment grows upward and the stack grows downward, so each can
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* take memory from the gap. If they meet, the process must be killed. The
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* procedures in this file deal with the growth of the data and stack segments.
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*
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* The entry points into this file are:
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* do_brk: BRK/SBRK system calls to grow or shrink the data segment
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* adjust: see if a proposed segment adjustment is allowed
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*/
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#define _SYSTEM 1
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#include <minix/callnr.h>
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#include <minix/com.h>
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#include <minix/config.h>
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#include <minix/const.h>
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#include <minix/ds.h>
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#include <minix/endpoint.h>
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#include <minix/keymap.h>
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#include <minix/minlib.h>
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#include <minix/type.h>
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#include <minix/ipc.h>
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#include <minix/sysutil.h>
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#include <minix/syslib.h>
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#include <minix/bitmap.h>
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#include <errno.h>
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#include <env.h>
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#include "glo.h"
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#include "vm.h"
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#include "proto.h"
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#include "util.h"
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#define DATA_CHANGED 1 /* flag value when data segment size changed */
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#define STACK_CHANGED 2 /* flag value when stack size changed */
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/*===========================================================================*
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* do_brk *
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*===========================================================================*/
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PUBLIC int do_brk(message *msg)
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{
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/* Perform the brk(addr) system call.
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* The parameter, 'addr' is the new virtual address in D space.
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*/
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int proc;
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if(vm_isokendpt(msg->VMB_ENDPOINT, &proc) != OK) {
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printf("VM: bogus endpoint VM_BRK %d\n", msg->VMB_ENDPOINT);
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return EINVAL;
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}
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return real_brk(&vmproc[proc], (vir_bytes) msg->VMB_ADDR);
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}
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/*===========================================================================*
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* adjust *
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*===========================================================================*/
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PUBLIC int adjust(rmp, data_clicks, sp)
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struct vmproc *rmp; /* whose memory is being adjusted? */
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vir_clicks data_clicks; /* how big is data segment to become? */
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vir_bytes sp; /* new value of sp */
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{
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/* See if data and stack segments can coexist, adjusting them if need be.
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* Memory is never allocated or freed. Instead it is added or removed from the
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* gap between data segment and stack segment. If the gap size becomes
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* negative, the adjustment of data or stack fails and ENOMEM is returned.
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*/
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register struct mem_map *mem_sp, *mem_dp;
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vir_clicks sp_click, gap_base, sp_lower, old_clicks;
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int changed, r, sp_in_dp;
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long base_of_stack, sp_delta; /* longs avoid certain problems */
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mem_dp = &rmp->vm_arch.vm_seg[D]; /* pointer to data segment map */
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mem_sp = &rmp->vm_arch.vm_seg[S]; /* pointer to stack segment map */
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changed = 0; /* set when either segment changed */
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/* See if stack size has gone negative (i.e., sp too close to 0xFFFF...) */
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base_of_stack = (long) mem_sp->mem_vir + (long) mem_sp->mem_len;
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sp_click = sp >> CLICK_SHIFT; /* click containing sp */
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if (sp_click >= base_of_stack)
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{
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return(ENOMEM); /* sp too high */
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}
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/* In order to support user-space libraries, processes might change sp to
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point to somewhere inside the data segment. If that's the case, be careful
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not to erroneously think that the data and stack have collided. */
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sp_in_dp = (mem_dp->mem_vir <= sp_click) &&
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(mem_dp->mem_vir + mem_dp->mem_len >= sp_click);
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/* Compute size of gap between stack and data segments. */
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sp_delta = (long) mem_sp->mem_vir - (long) sp_click;
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sp_lower = ((sp_delta > 0 && !sp_in_dp) ? sp_click : mem_sp->mem_vir);
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/* Add a safety margin for future stack growth. Impossible to do right. */
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#define SAFETY_BYTES (384 * sizeof(char *))
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#define SAFETY_CLICKS ((vir_clicks) (CLICK_CEIL(SAFETY_BYTES) >> CLICK_SHIFT))
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gap_base = mem_dp->mem_vir + data_clicks + SAFETY_CLICKS;
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if (sp_lower < gap_base)
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{
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return(ENOMEM); /* data and stack collided */
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}
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/* Update data length (but not data orgin) on behalf of brk() system call. */
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old_clicks = mem_dp->mem_len;
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if (data_clicks != mem_dp->mem_len) {
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mem_dp->mem_len = data_clicks;
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changed |= DATA_CHANGED;
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}
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/* Update stack length and origin due to change in stack pointer. */
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if (sp_delta > 0 && !sp_in_dp) {
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mem_sp->mem_vir -= sp_delta;
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mem_sp->mem_phys -= sp_delta;
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mem_sp->mem_len += sp_delta;
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changed |= STACK_CHANGED;
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}
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/* Do the new data and stack segment sizes fit in the address space? */
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r = (rmp->vm_arch.vm_seg[D].mem_vir + rmp->vm_arch.vm_seg[D].mem_len >
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rmp->vm_arch.vm_seg[S].mem_vir) ? ENOMEM : OK;
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if(r == OK && (rmp->vm_flags & VMF_HASPT) &&
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rmp->vm_endpoint != VM_PROC_NR && rmp->vm_heap) {
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if(old_clicks < data_clicks) {
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vir_bytes more;
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more = (data_clicks - old_clicks) << CLICK_SHIFT;
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if(map_region_extend(rmp, rmp->vm_heap, more) != OK) {
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printf("VM: brk: map_region_extend failed\n");
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return ENOMEM;
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}
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} else if(old_clicks > data_clicks) {
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vir_bytes less;
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less = (old_clicks - data_clicks) << CLICK_SHIFT;
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if(map_region_shrink(rmp->vm_heap, less) != OK) {
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printf("VM: brk: map_region_shrink failed\n");
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return ENOMEM;
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}
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}
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}
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if (r == OK)
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return(OK);
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/* New sizes don't fit or require too many page/segment registers. Restore.*/
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if (changed & DATA_CHANGED) mem_dp->mem_len = old_clicks;
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if (changed & STACK_CHANGED) {
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mem_sp->mem_vir += sp_delta;
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mem_sp->mem_phys += sp_delta;
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mem_sp->mem_len -= sp_delta;
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}
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return(ENOMEM);
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}
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/*===========================================================================*
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* real_brk *
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*===========================================================================*/
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PUBLIC int real_brk(vmp, v)
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struct vmproc *vmp;
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vir_bytes v;
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{
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vir_bytes new_sp;
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vir_clicks new_clicks;
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int r;
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new_clicks = (vir_clicks) (CLICK_CEIL(v) >> CLICK_SHIFT);
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if (new_clicks < vmp->vm_arch.vm_seg[D].mem_vir) {
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printf("VM: real_brk failed because new_clicks too high: %d\n",
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new_clicks);
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return(ENOMEM);
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}
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new_clicks -= vmp->vm_arch.vm_seg[D].mem_vir;
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if ((r=get_stack_ptr(vmp->vm_endpoint, &new_sp)) != OK)
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panic("couldn't get stack pointer: %d", r);
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r = adjust(vmp, new_clicks, new_sp);
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return r;
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}
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