119 lines
2.4 KiB
C
119 lines
2.4 KiB
C
#include <stdlib.h>
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#include <stdint.h>
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#include <limits.h>
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#include <errno.h>
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#include <sys/mman.h>
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#include "libc.h"
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#include "lock.h"
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#include "syscall.h"
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#include "fork_impl.h"
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#define ALIGN 16
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/* This function returns true if the interval [old,new]
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* intersects the 'len'-sized interval below &libc.auxv
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* (interpreted as the main-thread stack) or below &b
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* (the current stack). It is used to defend against
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* buggy brk implementations that can cross the stack. */
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static int traverses_stack_p(uintptr_t old, uintptr_t new)
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{
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const uintptr_t len = 8<<20;
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uintptr_t a, b;
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b = (uintptr_t)libc.auxv;
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a = b > len ? b-len : 0;
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if (new>a && old<b) return 1;
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b = (uintptr_t)&b;
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a = b > len ? b-len : 0;
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if (new>a && old<b) return 1;
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return 0;
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}
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static volatile int lock[1];
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volatile int *const __bump_lockptr = lock;
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static void *__simple_malloc(size_t n)
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{
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static uintptr_t brk, cur, end;
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static unsigned mmap_step;
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size_t align=1;
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void *p;
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if (n > SIZE_MAX/2) {
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errno = ENOMEM;
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return 0;
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}
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if (!n) n++;
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while (align<n && align<ALIGN)
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align += align;
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LOCK(lock);
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cur += -cur & align-1;
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if (n > end-cur) {
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size_t req = n - (end-cur) + PAGE_SIZE-1 & -PAGE_SIZE;
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if (!cur) {
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brk = __syscall(SYS_brk, 0);
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brk += -brk & PAGE_SIZE-1;
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cur = end = brk;
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}
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if (brk == end && req < SIZE_MAX-brk
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&& !traverses_stack_p(brk, brk+req)
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&& __syscall(SYS_brk, brk+req)==brk+req) {
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brk = end += req;
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} else {
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int new_area = 0;
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req = n + PAGE_SIZE-1 & -PAGE_SIZE;
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/* Only make a new area rather than individual mmap
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* if wasted space would be over 1/8 of the map. */
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if (req-n > req/8) {
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/* Geometric area size growth up to 64 pages,
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* bounding waste by 1/8 of the area. */
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size_t min = PAGE_SIZE<<(mmap_step/2);
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if (min-n > end-cur) {
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if (req < min) {
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req = min;
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if (mmap_step < 12)
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mmap_step++;
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}
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new_area = 1;
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}
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}
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void *mem = __mmap(0, req, PROT_READ|PROT_WRITE,
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MAP_PRIVATE|MAP_ANONYMOUS, -1, 0);
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if (mem == MAP_FAILED || !new_area) {
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UNLOCK(lock);
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return mem==MAP_FAILED ? 0 : mem;
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}
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cur = (uintptr_t)mem;
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end = cur + req;
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}
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}
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p = (void *)cur;
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cur += n;
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UNLOCK(lock);
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return p;
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}
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weak_alias(__simple_malloc, __libc_malloc_impl);
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void *__libc_malloc(size_t n)
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{
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return __libc_malloc_impl(n);
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}
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static void *default_malloc(size_t n)
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{
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return __libc_malloc_impl(n);
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}
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weak_alias(default_malloc, malloc);
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