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/* SPDX-License-Identifier: GPL-2.0-only OR GPL-3.0-only */
/* Copyright (c) 2021-2022 Brett Sheffield <bacs@librecast.net> */
#define _GNU_SOURCE
#include <dlfcn.h>
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
static volatile int allock;
static size_t stackptr;
static char stackbuf[1024];
static void *(*_malloc)(size_t);
static void (*_free)(void *);
static int falloc_fail = -1; /* *alloc fails when zero - decremented each allocation */
static void *falloc_enomem(void)
{
fprintf(stderr, "falloc forcing ENOMEM\n");
errno = ENOMEM;
return NULL;
}
void *malloc(size_t size)
{
if (allock) {
/* thanks to FatalFlaw for the idea
* https://stackoverflow.com/questions/6083337/overriding-malloc-using-the-ld-preload-mechanism */
/* dlsym calls calloc() - hand it a block from our stack */
void *p;
p = stackbuf + stackptr;
stackptr += size;
return p;
}
else if (!_malloc) {
allock = 1;
*(void **)&_malloc = dlsym(RTLD_NEXT, "malloc");
*(void **)&_free = dlsym(RTLD_NEXT, "free");
allock = 0;
}
if (falloc_fail > 0) falloc_fail--;
if (!falloc_fail) return falloc_enomem();
return _malloc(size);
}
void *calloc(size_t nmemb, size_t size)
{
void *ptr;
size_t sz = nmemb * size;
ptr = malloc(sz);
if (!ptr) return NULL;
memset(ptr, 0, sz);
return ptr;
}
void free(void *ptr)
{
if (!ptr) return;
if ((char *)ptr < stackbuf || (char *)ptr > stackbuf + sizeof stackbuf)
_free(ptr);
}
void falloc_setfail(int failafter)
{
falloc_fail = failafter;
}
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