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/*
* Copyright 2019 The Emscripten Authors. All rights reserved.
* Emscripten is available under two separate licenses, the MIT license and the
* University of Illinois/NCSA Open Source License. Both these licenses can be
* found in the LICENSE file.
*
*/
// libc files are compiled as -std=c99 which doesn't normally declare
// max_align_t.
#if __STDC_VERSION__ < 201112L
#define __NEED_max_align_t
#endif
#include <errno.h>
#include <limits.h>
#include <stddef.h>
#include <stdint.h>
#ifdef __EMSCRIPTEN_SHARED_MEMORY__ // for error handling, see below
#include <stdio.h>
#include <stdlib.h>
#endif
#ifdef __EMSCRIPTEN_TRACING__
void emscripten_memprof_sbrk_grow(intptr_t old, intptr_t new);
#else
#define emscripten_memprof_sbrk_grow(...) ((void)0)
#endif
#include <emscripten/heap.h>
extern size_t __heap_base;
static uintptr_t sbrk_val = (uintptr_t)&__heap_base;
uintptr_t* emscripten_get_sbrk_ptr() {
#ifdef __PIC__
// In relocatable code we may call emscripten_get_sbrk_ptr() during startup,
// potentially *before* the setup of the dynamically-linked __heap_base, when
// using SAFE_HEAP. (SAFE_HEAP instruments *all* memory accesses, so even the
// code doing dynamic linking itself ends up instrumented, which is why we can
// get such an instrumented call before sbrk_val has its proper value.)
if (sbrk_val == 0) {
sbrk_val = (uintptr_t)&__heap_base;
}
#endif
return &sbrk_val;
}
// Enforce preserving a minimal alignof(maxalign_t) alignment for sbrk.
#define SBRK_ALIGNMENT (__alignof__(max_align_t))
#ifdef __EMSCRIPTEN_SHARED_MEMORY__
#define READ_SBRK_PTR(sbrk_ptr) (__c11_atomic_load((_Atomic(uintptr_t)*)(sbrk_ptr), __ATOMIC_SEQ_CST))
#else
#define READ_SBRK_PTR(sbrk_ptr) (*(sbrk_ptr))
#endif
void *sbrk(intptr_t increment_) {
uintptr_t increment = (uintptr_t)increment_;
increment = (increment + (SBRK_ALIGNMENT-1)) & ~(SBRK_ALIGNMENT-1);
uintptr_t *sbrk_ptr = (uintptr_t*)emscripten_get_sbrk_ptr();
// To make sbrk thread-safe, implement a CAS loop to update the
// value of sbrk_ptr.
while (1) {
uintptr_t old_brk = READ_SBRK_PTR(sbrk_ptr);
uintptr_t new_brk = old_brk + increment;
// Check for a) an overflow, which would indicate that we are trying to
// allocate over maximum addressable memory. and b) if necessary,
// increase the WebAssembly Memory size, and abort if that fails.
if ((increment > 0 && new_brk <= old_brk)
|| (new_brk > emscripten_get_heap_size() && !emscripten_resize_heap(new_brk))) {
errno = ENOMEM;
return (void*)-1;
}
#ifdef __EMSCRIPTEN_SHARED_MEMORY__
// Attempt to update the dynamic top to new value. Another thread may have
// beat this one to the update, in which case we will need to start over
// by iterating the loop body again.
uintptr_t expected = old_brk;
__c11_atomic_compare_exchange_strong((_Atomic(uintptr_t)*)sbrk_ptr,
&expected, new_brk, __ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST);
if (expected != old_brk) continue; // CAS failed, another thread raced in between.
#else
*sbrk_ptr = new_brk;
#endif
emscripten_memprof_sbrk_grow(old_brk, new_brk);
return (void*)old_brk;
}
}
int brk(void* ptr) {
#ifdef __EMSCRIPTEN_SHARED_MEMORY__
// FIXME
printf("brk() is not theadsafe yet, https://github.com/emscripten-core/emscripten/issues/10006");
abort();
#else
uintptr_t last = (uintptr_t)sbrk(0);
if (sbrk((uintptr_t)ptr - last) == (void*)-1) {
return -1;
}
return 0;
#endif
}
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