118 lines
3.8 KiB
C
118 lines
3.8 KiB
C
/* Minimal malloc implementation for dynamic linker and static
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initialization.
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Copyright (C) 1995-2022 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<https://www.gnu.org/licenses/>. */
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/* Mark symbols hidden in static PIE for early self relocation to work.
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Note: string.h may have ifuncs which cannot be hidden on i686. */
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#if BUILD_PIE_DEFAULT
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# pragma GCC visibility push(hidden)
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#endif
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#include <assert.h>
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#include <string.h>
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#include <ldsodefs.h>
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#include <malloc/malloc-internal.h>
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static void *alloc_ptr, *alloc_end, *alloc_last_block;
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/* Allocate an aligned memory block. */
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void *
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__minimal_malloc (size_t n)
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{
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if (alloc_end == 0)
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{
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/* Consume any unused space in the last page of our data segment. */
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extern int _end attribute_hidden;
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alloc_ptr = &_end;
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alloc_end = (void *) 0 + (((alloc_ptr - (void *) 0)
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+ GLRO(dl_pagesize) - 1)
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& ~(GLRO(dl_pagesize) - 1));
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}
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/* Make sure the allocation pointer is ideally aligned. */
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alloc_ptr = (void *) 0 + (((alloc_ptr - (void *) 0) + MALLOC_ALIGNMENT - 1)
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& ~(MALLOC_ALIGNMENT - 1));
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if (alloc_ptr + n >= alloc_end || n >= -(uintptr_t) alloc_ptr)
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{
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/* Insufficient space left; allocate another page plus one extra
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page to reduce number of mmap calls. */
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caddr_t page;
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size_t nup = (n + GLRO(dl_pagesize) - 1) & ~(GLRO(dl_pagesize) - 1);
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if (__glibc_unlikely (nup == 0 && n != 0))
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return NULL;
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nup += GLRO(dl_pagesize);
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page = __mmap (0, nup, PROT_READ|PROT_WRITE,
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MAP_ANON|MAP_PRIVATE, -1, 0);
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if (page == MAP_FAILED)
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return NULL;
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if (page != alloc_end)
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alloc_ptr = page;
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alloc_end = page + nup;
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}
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alloc_last_block = (void *) alloc_ptr;
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alloc_ptr += n;
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return alloc_last_block;
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}
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/* We use this function occasionally since the real implementation may
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be optimized when it can assume the memory it returns already is
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set to NUL. */
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void *
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__minimal_calloc (size_t nmemb, size_t size)
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{
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/* New memory from the trivial malloc above is always already cleared.
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(We make sure that's true in the rare occasion it might not be,
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by clearing memory in free, below.) */
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size_t bytes = nmemb * size;
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#define HALF_SIZE_T (((size_t) 1) << (8 * sizeof (size_t) / 2))
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if (__builtin_expect ((nmemb | size) >= HALF_SIZE_T, 0)
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&& size != 0 && bytes / size != nmemb)
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return NULL;
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return malloc (bytes);
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}
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/* This will rarely be called. */
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void
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__minimal_free (void *ptr)
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{
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/* We can free only the last block allocated. */
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if (ptr == alloc_last_block)
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{
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/* Since this is rare, we clear the freed block here
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so that calloc can presume malloc returns cleared memory. */
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memset (alloc_last_block, '\0', alloc_ptr - alloc_last_block);
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alloc_ptr = alloc_last_block;
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}
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}
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/* This is only called with the most recent block returned by malloc. */
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void *
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__minimal_realloc (void *ptr, size_t n)
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{
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if (ptr == NULL)
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return malloc (n);
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assert (ptr == alloc_last_block);
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size_t old_size = alloc_ptr - alloc_last_block;
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alloc_ptr = alloc_last_block;
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void *new = malloc (n);
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return new != ptr ? memcpy (new, ptr, old_size) : new;
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}
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