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/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8 :vi│
╞══════════════════════════════════════════════════════════════════════════════╡
│ Copyright 2020 Justine Alexandra Roberts Tunney │
│ │
│ This program is free software; you can redistribute it and/or modify │
│ it under the terms of the GNU General Public License as published by │
│ the Free Software Foundation; version 2 of the License. │
│ │
│ This program is distributed in the hope that it will be useful, but │
│ WITHOUT ANY WARRANTY; without even the implied warranty of │
│ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU │
│ General Public License for more details. │
│ │
│ You should have received a copy of the GNU General Public License │
│ along with this program; if not, write to the Free Software │
│ Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA │
│ 02110-1301 USA │
╚─────────────────────────────────────────────────────────────────────────────*/
#include "libc/assert.h"
#include "libc/bits/bits.h"
#include "libc/bits/popcnt.h"
#include "libc/bits/safemacros.h"
#include "libc/calls/calls.h"
#include "libc/runtime/buffer.h"
#include "libc/runtime/mappings.h"
#include "libc/runtime/runtime.h"
#include "libc/str/str.h"
#include "libc/sysv/consts/prot.h"
#define kGuard PAGESIZE
#define kGrain FRAMESIZE
/**
* Allocates page-guarded buffer.
*
* ┌─────────────────────────────────────┬s─i─g─s─e─g─v┐
* │ 𝑣₀..𝑣ₙ₋₁ │𝑣ₙ..𝑣ₙ₊₄₀₉₆₋₁│
* └─────────────────────────────────────┴s─i─g─s─e─g─v┘
*
* @param b is metadata object owned by caller, initialized to zero for
* first call; subsequent calls will resize
* @param a is alignment requirement in bytes, e.g. 1,2,4,8,16,...
* @param n is buffer size in bytes
* @return b->p
* @see ralloc()
*/
void *balloc(struct GuardedBuffer *b, unsigned a, size_t n) {
int rc;
char *p;
size_t mi, need;
struct AddrSize az;
struct MemoryCoord mc;
assert(a >= 1);
assert(a <= kGuard);
assert(kGuard < kGrain);
assert(popcnt(a) == 1);
assert(popcnt(kGuard) == 1);
assert(popcnt(kGrain) == 1);
assert(n < 0x800000000000ul - kGrain - kGuard);
if (n) {
az.addr = 0;
az.size = 0;
n = roundup(n, a);
need = roundup(n + kGuard, kGrain);
if (b->p) {
mc = ADDRSIZE_TO_COORD(b->p, 1);
mi = findmapping(mc.y);
if (mi && ISOVERLAPPING(mc, _mm.p[mi - 1])) {
az = COORD_TO_ADDRSIZE(_mm.p[mi - 1]);
if (az.size < need) {
rc = munmap(az.addr, az.size);
assert(rc != -1);
az.addr = NULL;
az.size = 0;
}
}
}
if (!az.size) {
if ((p = mapanon(need)) == MAP_FAILED) abort();
if (mprotect(p + need - kGuard, kGuard, PROT_NONE) == -1) abort();
} else {
p = az.addr;
}
b->p = p + need - kGuard - n;
}
return b->p;
}