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