Lennart Poettering
319a4f4bc4
We recently started making more use of malloc_usable_size() and rely on it (see the string_erase() story). Given that we don't really support sytems where malloc_usable_size() cannot be trusted beyond statistics anyway, let's go fully in and rework GREEDY_REALLOC() on top of it: instead of passing around and maintaining the currenly allocated size everywhere, let's just derive it automatically from malloc_usable_size(). I am mostly after this for the simplicity this brings. It also brings minor efficiency improvements I guess, but things become so much nicer to look at if we can avoid these allocation size variables everywhere. Note that the malloc_usable_size() man page says relying on it wasn't "good programming practice", but I think it does this for reasons that don't apply here: the greedy realloc logic specifically doesn't rely on the returned extra size, beyond the fact that it is equal or larger than what was requested. (This commit was supposed to be a quick patch btw, but apparently we use the greedy realloc stuff quite a bit across the codebase, so this ends up touching *a*lot* of code.)
106 lines
2.5 KiB
C
106 lines
2.5 KiB
C
/* SPDX-License-Identifier: LGPL-2.1-or-later */
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#include <malloc.h>
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#include <stdint.h>
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#include <string.h>
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#include "alloc-util.h"
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#include "macro.h"
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#include "memory-util.h"
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void* memdup(const void *p, size_t l) {
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void *ret;
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assert(l == 0 || p);
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ret = malloc(l ?: 1);
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if (!ret)
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return NULL;
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memcpy(ret, p, l);
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return ret;
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}
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void* memdup_suffix0(const void *p, size_t l) {
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void *ret;
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assert(l == 0 || p);
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/* The same as memdup() but place a safety NUL byte after the allocated memory */
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if (_unlikely_(l == SIZE_MAX)) /* prevent overflow */
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return NULL;
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ret = malloc(l + 1);
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if (!ret)
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return NULL;
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*((uint8_t*) mempcpy(ret, p, l)) = 0;
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return ret;
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}
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void* greedy_realloc(
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void **p,
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size_t need,
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size_t size) {
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size_t a, newalloc;
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void *q;
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assert(p);
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/* We use malloc_usable_size() for determining the current allocated size. On all systems we care
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* about this should be safe to rely on. Should there ever arise the need to avoid relying on this we
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* can instead locally fall back to realloc() on every call, rounded up to the next exponent of 2 or
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* so. */
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if (*p && (size == 0 || (MALLOC_SIZEOF_SAFE(*p) / size >= need)))
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return *p;
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if (_unlikely_(need > SIZE_MAX/2)) /* Overflow check */
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return NULL;
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newalloc = need * 2;
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if (size_multiply_overflow(newalloc, size))
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return NULL;
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a = newalloc * size;
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if (a < 64) /* Allocate at least 64 bytes */
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a = 64;
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q = realloc(*p, a);
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if (!q)
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return NULL;
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return *p = q;
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}
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void* greedy_realloc0(
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void **p,
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size_t need,
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size_t size) {
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size_t before, after;
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uint8_t *q;
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assert(p);
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before = MALLOC_SIZEOF_SAFE(*p); /* malloc_usable_size() will return 0 on NULL input, as per docs */
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q = greedy_realloc(p, need, size);
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if (!q)
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return NULL;
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after = MALLOC_SIZEOF_SAFE(q);
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if (size == 0) /* avoid division by zero */
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before = 0;
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else
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before = (before / size) * size; /* Round down */
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if (after > before)
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memzero(q + before, after - before);
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return q;
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}
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