allow sbrk(-x) to de-allocate user memory

This commit is contained in:
Robert Morris 2010-08-10 17:08:41 -04:00
parent c4cc10da7e
commit 83d2db91f7
4 changed files with 89 additions and 4 deletions

1
defs.h
View file

@ -159,6 +159,7 @@ void vminit(void);
pde_t* setupkvm(void); pde_t* setupkvm(void);
char* uva2ka(pde_t*, char*); char* uva2ka(pde_t*, char*);
int allocuvm(pde_t*, char*, uint); int allocuvm(pde_t*, char*, uint);
int deallocuvm(pde_t *pgdir, char *addr, uint sz);
void freevm(pde_t*); void freevm(pde_t*);
void inituvm(pde_t*, char*, char*, uint); void inituvm(pde_t*, char*, char*, uint);
int loaduvm(pde_t*, char*, struct inode *ip, uint, uint); int loaduvm(pde_t*, char*, struct inode *ip, uint, uint);

5
proc.c
View file

@ -142,8 +142,13 @@ userinit(void)
int int
growproc(int n) growproc(int n)
{ {
if(n > 0){
if (!allocuvm(proc->pgdir, (char *)proc->sz, n)) if (!allocuvm(proc->pgdir, (char *)proc->sz, n))
return -1; return -1;
} else if(n < 0){
if (!deallocuvm(proc->pgdir, (char *)(proc->sz + n), 0 - n))
return -1;
}
proc->sz += n; proc->sz += n;
switchuvm(proc); switchuvm(proc);
return 0; return 0;

View file

@ -1232,7 +1232,11 @@ forktest(void)
void void
sbrktest(void) sbrktest(void)
{ {
int pid;
printf(stdout, "sbrk test\n"); printf(stdout, "sbrk test\n");
// can one sbrk() less than a page?
char *a = sbrk(0); char *a = sbrk(0);
int i; int i;
for(i = 0; i < 5000; i++){ for(i = 0; i < 5000; i++){
@ -1244,7 +1248,7 @@ sbrktest(void)
*b = 1; *b = 1;
a = b + 1; a = b + 1;
} }
int pid = fork(); pid = fork();
if(pid < 0){ if(pid < 0){
printf(stdout, "sbrk test fork failed\n"); printf(stdout, "sbrk test fork failed\n");
exit(); exit();
@ -1258,6 +1262,57 @@ sbrktest(void)
if(pid == 0) if(pid == 0)
exit(); exit();
wait(); wait();
// can one allocate the full 640K?
a = sbrk(0);
uint amt = (640 * 1024) - (uint) a;
char *p = sbrk(amt);
if(p != a){
printf(stdout, "sbrk test failed 640K test, p %x a %x\n", p, a);
exit();
}
char *lastaddr = (char *)(640 * 1024 - 1);
*lastaddr = 99;
// is one forbidden from allocating more than 640K?
c = sbrk(4096);
if(c != (char *) 0xffffffff){
printf(stdout, "sbrk allocated more than 640K, c %x\n", c);
exit();
}
// can one de-allocate?
a = sbrk(0);
c = sbrk(-4096);
if(c == (char *) 0xffffffff){
printf(stdout, "sbrk could not deallocate\n");
exit();
}
c = sbrk(0);
if(c != a - 4096){
printf(stdout, "sbrk deallocation produced wrong address, a %x c %x\n", a, c);
exit();
}
// can one re-allocate that page?
a = sbrk(0);
c = sbrk(4096);
if(c != a || sbrk(0) != a + 4096){
printf(stdout, "sbrk re-allocation failed, a %x c %x\n", a, c);
exit();
}
if(*lastaddr == 99){
// should be zero
printf(stdout, "sbrk de-allocation didn't really deallocate\n");
exit();
}
c = sbrk(4096);
if(c != (char *) 0xffffffff){
printf(stdout, "sbrk was able to re-allocate beyond 640K, c %x\n", c);
exit();
}
printf(stdout, "sbrk test OK\n"); printf(stdout, "sbrk test OK\n");
} }

26
vm.c
View file

@ -198,7 +198,7 @@ uva2ka(pde_t *pgdir, char *uva)
int int
allocuvm(pde_t *pgdir, char *addr, uint sz) allocuvm(pde_t *pgdir, char *addr, uint sz)
{ {
if (addr + sz >= (char*)USERTOP) if (addr + sz > (char*)USERTOP)
return 0; return 0;
char *first = PGROUNDDOWN(addr); char *first = PGROUNDDOWN(addr);
char *last = PGROUNDDOWN(addr + sz - 1); char *last = PGROUNDDOWN(addr + sz - 1);
@ -218,6 +218,30 @@ allocuvm(pde_t *pgdir, char *addr, uint sz)
return 1; return 1;
} }
// deallocate some of the user pages, in response to sbrk()
// with a negative argument. if addr is not page-aligned,
// then only deallocates starting at the next page boundary.
int
deallocuvm(pde_t *pgdir, char *addr, uint sz)
{
if (addr + sz > (char*)USERTOP)
return 0;
char *first = (char*) PGROUNDUP((uint)addr);
char *last = PGROUNDDOWN(addr + sz - 1);
char *a;
for(a = first; a <= last; a += PGSIZE){
pte_t *pte = walkpgdir(pgdir, a, 0);
if(pte && (*pte & PTE_P) != 0){
uint pa = PTE_ADDR(*pte);
if(pa == 0)
panic("deallocuvm");
kfree((void *) pa, PGSIZE);
*pte = 0;
}
}
return 1;
}
// free a page table and all the physical memory pages // free a page table and all the physical memory pages
// in the user part. // in the user part.
void void