diff options
| -rw-r--r-- | src/malloc/lite_malloc.c | 89 |
1 files changed, 72 insertions, 17 deletions
diff --git a/src/malloc/lite_malloc.c b/src/malloc/lite_malloc.c index 050d84f6..c3f0c129 100644 --- a/src/malloc/lite_malloc.c +++ b/src/malloc/lite_malloc.c @@ -2,44 +2,99 @@ #include <stdint.h> #include <limits.h> #include <errno.h> +#include <sys/mman.h> +#include "libc.h" #include "lock.h" -#include "malloc_impl.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 char *cur, *end; + static uintptr_t brk, cur, end; static volatile int lock[1]; - size_t align=1, pad; + 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); - pad = -(uintptr_t)cur & align-1; - - if (n <= SIZE_MAX/2 + ALIGN) n += pad; + cur += -cur & align-1; if (n > end-cur) { - size_t m = n; - char *new = __expand_heap(&m); - if (!new) { - UNLOCK(lock); - return 0; + 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 (new != end) { - cur = new; - n -= pad; - pad = 0; + + 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; } - end = new + m; } - p = cur + pad; + p = (void *)cur; cur += n; UNLOCK(lock); return p; |