1#include <stdlib.h>
  2#include <stdint.h>
  3#include <limits.h>
  4#include <errno.h>
  5#include <sys/mman.h>
  6#include "libc.h"
  7#include "lock.h"
  8#include "syscall.h"
  9#include "fork_impl.h"
 10
 11#define ALIGN 16
 12
 13/* This function returns true if the interval [old,new]
 14 * intersects the 'len'-sized interval below &libc.auxv
 15 * (interpreted as the main-thread stack) or below &b
 16 * (the current stack). It is used to defend against
 17 * buggy brk implementations that can cross the stack. */
 18
 19static int traverses_stack_p(uintptr_t old, uintptr_t new)
 20{
 21	const uintptr_t len = 8<<20;
 22	uintptr_t a, b;
 23
 24	b = (uintptr_t)libc.auxv;
 25	a = b > len ? b-len : 0;
 26	if (new>a && old<b) return 1;
 27
 28	b = (uintptr_t)&b;
 29	a = b > len ? b-len : 0;
 30	if (new>a && old<b) return 1;
 31
 32	return 0;
 33}
 34
 35static volatile int lock[1];
 36volatile int *const __bump_lockptr = lock;
 37
 38static void *__simple_malloc(size_t n)
 39{
 40	static uintptr_t brk, cur, end;
 41	static unsigned mmap_step;
 42	size_t align=1;
 43	void *p;
 44
 45	if (n > SIZE_MAX/2) {
 46		errno = ENOMEM;
 47		return 0;
 48	}
 49
 50	if (!n) n++;
 51	while (align<n && align<ALIGN)
 52		align += align;
 53
 54	LOCK(lock);
 55
 56	cur += -cur & align-1;
 57
 58	if (n > end-cur) {
 59		size_t req = n - (end-cur) + PAGE_SIZE-1 & -PAGE_SIZE;
 60
 61		if (!cur) {
 62			brk = __syscall(SYS_brk, 0);
 63			brk += -brk & PAGE_SIZE-1;
 64			cur = end = brk;
 65		}
 66
 67		if (brk == end && req < SIZE_MAX-brk
 68		    && !traverses_stack_p(brk, brk+req)
 69		    && __syscall(SYS_brk, brk+req)==brk+req) {
 70			brk = end += req;
 71		} else {
 72			int new_area = 0;
 73			req = n + PAGE_SIZE-1 & -PAGE_SIZE;
 74			/* Only make a new area rather than individual mmap
 75			 * if wasted space would be over 1/8 of the map. */
 76			if (req-n > req/8) {
 77				/* Geometric area size growth up to 64 pages,
 78				 * bounding waste by 1/8 of the area. */
 79				size_t min = PAGE_SIZE<<(mmap_step/2);
 80				if (min-n > end-cur) {
 81					if (req < min) {
 82						req = min;
 83						if (mmap_step < 12)
 84							mmap_step++;
 85					}
 86					new_area = 1;
 87				}
 88			}
 89			void *mem = __mmap(0, req, PROT_READ|PROT_WRITE,
 90				MAP_PRIVATE|MAP_ANONYMOUS, -1, 0);
 91			if (mem == MAP_FAILED || !new_area) {
 92				UNLOCK(lock);
 93				return mem==MAP_FAILED ? 0 : mem;
 94			}
 95			cur = (uintptr_t)mem;
 96			end = cur + req;
 97		}
 98	}
 99
100	p = (void *)cur;
101	cur += n;
102	UNLOCK(lock);
103	return p;
104}
105
106weak_alias(__simple_malloc, __libc_malloc_impl);
107
108void *__libc_malloc(size_t n)
109{
110	return __libc_malloc_impl(n);
111}
112
113static void *default_malloc(size_t n)
114{
115	return __libc_malloc_impl(n);
116}
117
118weak_alias(default_malloc, malloc);