171 lines
6.4 KiB
C
171 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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* size_ok: see if the segment sizes are feasible
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*/
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#include "mm.h"
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#include <signal.h>
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#include "mproc.h"
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#include "param.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()
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{
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/* Perform the brk(addr) system call.
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*
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* The call is complicated by the fact that on some machines (e.g., 8088),
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* the stack pointer can grow beyond the base of the stack segment without
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* anybody noticing it.
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* The parameter, 'addr' is the new virtual address in D space.
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*/
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register struct mproc *rmp;
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int r;
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vir_bytes v, new_sp;
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vir_clicks new_clicks;
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rmp = mp;
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v = (vir_bytes) m_in.addr;
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new_clicks = (vir_clicks) ( ((long) v + CLICK_SIZE - 1) >> CLICK_SHIFT);
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if (new_clicks < rmp->mp_seg[D].mem_vir) {
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rmp->mp_reply.reply_ptr = (char *) -1;
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return(ENOMEM);
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}
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new_clicks -= rmp->mp_seg[D].mem_vir;
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if ((r=p_getsp(who, &new_sp)) != OK) /* ask kernel for current sp value */
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panic("MM couldn't get stack pointer", r);
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r = adjust(rmp, new_clicks, new_sp);
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rmp->mp_reply.reply_ptr = (r == OK ? m_in.addr : (char *) -1);
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return(r); /* return new address or -1 */
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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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register struct mproc *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, lower, old_clicks;
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int changed, r, ft;
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long base_of_stack, delta; /* longs avoid certain problems */
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mem_dp = &rmp->mp_seg[D]; /* pointer to data segment map */
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mem_sp = &rmp->mp_seg[S]; /* pointer to stack segment map */
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changed = 0; /* set when either segment changed */
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if (mem_sp->mem_len == 0) return(OK); /* don't bother init */
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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) return(ENOMEM); /* sp too high */
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/* Compute size of gap between stack and data segments. */
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delta = (long) mem_sp->mem_vir - (long) sp_click;
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lower = (delta > 0 ? 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 ((SAFETY_BYTES + CLICK_SIZE - 1) / CLICK_SIZE)
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gap_base = mem_dp->mem_vir + data_clicks + SAFETY_CLICKS;
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if (lower < gap_base) return(ENOMEM); /* data and stack collided */
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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 (delta > 0) {
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mem_sp->mem_vir -= delta;
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mem_sp->mem_phys -= delta;
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mem_sp->mem_len += 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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ft = (rmp->mp_flags & SEPARATE);
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r = size_ok(ft, rmp->mp_seg[T].mem_len, rmp->mp_seg[D].mem_len,
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rmp->mp_seg[S].mem_len, rmp->mp_seg[D].mem_vir, rmp->mp_seg[S].mem_vir);
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if (r == OK) {
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if (changed) sys_newmap((int)(rmp - mproc), rmp->mp_seg);
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return(OK);
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}
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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 += delta;
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mem_sp->mem_phys += delta;
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mem_sp->mem_len -= delta;
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}
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return(ENOMEM);
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}
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/*===========================================================================*
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* size_ok *
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*===========================================================================*/
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PUBLIC int size_ok(file_type, tc, dc, sc, dvir, s_vir)
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int file_type; /* SEPARATE or 0 */
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vir_clicks tc; /* text size in clicks */
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vir_clicks dc; /* data size in clicks */
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vir_clicks sc; /* stack size in clicks */
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vir_clicks dvir; /* virtual address for start of data seg */
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vir_clicks s_vir; /* virtual address for start of stack seg */
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{
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/* Check to see if the sizes are feasible and enough segmentation registers
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* exist. On a machine with eight 8K pages, text, data, stack sizes of
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* (32K, 16K, 16K) will fit, but (33K, 17K, 13K) will not, even though the
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* former is bigger (64K) than the latter (63K). Even on the 8088 this test
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* is needed, since the data and stack may not exceed 4096 clicks.
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*/
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#if (CHIP == INTEL && _WORD_SIZE == 2)
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int pt, pd, ps; /* segment sizes in pages */
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pt = ( (tc << CLICK_SHIFT) + PAGE_SIZE - 1)/PAGE_SIZE;
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pd = ( (dc << CLICK_SHIFT) + PAGE_SIZE - 1)/PAGE_SIZE;
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ps = ( (sc << CLICK_SHIFT) + PAGE_SIZE - 1)/PAGE_SIZE;
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if (file_type == SEPARATE) {
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if (pt > MAX_PAGES || pd + ps > MAX_PAGES) return(ENOMEM);
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} else {
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if (pt + pd + ps > MAX_PAGES) return(ENOMEM);
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}
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#endif
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if (dvir + dc > s_vir) return(ENOMEM);
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return(OK);
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}
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