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/* Minimal malloc implementation for dynamic linker and static
initialization.
Copyright (C) 1995-2024 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library 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
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<https://www.gnu.org/licenses/>. */
/* Mark symbols hidden in static PIE for early self relocation to work.
Note: string.h may have ifuncs which cannot be hidden on i686. */
#if BUILD_PIE_DEFAULT
# pragma GCC visibility push(hidden)
#endif
#include <assert.h>
#include <string.h>
#include <ldsodefs.h>
#include <malloc/malloc-internal.h>
#include <setvmaname.h>
static void *alloc_ptr, *alloc_end, *alloc_last_block;
/* Allocate an aligned memory block. */
void *
__minimal_malloc (size_t n)
{
if (alloc_end == 0)
{
/* Consume any unused space in the last page of our data segment. */
extern int _end attribute_hidden;
alloc_ptr = &_end;
alloc_end = (void *) 0 + ((((uintptr_t) alloc_ptr)
+ GLRO(dl_pagesize) - 1)
& ~(GLRO(dl_pagesize) - 1));
}
/* Make sure the allocation pointer is ideally aligned. */
alloc_ptr = (void *) 0 + ((((uintptr_t) alloc_ptr) + MALLOC_ALIGNMENT - 1)
& ~(MALLOC_ALIGNMENT - 1));
if (alloc_ptr + n >= alloc_end || n >= -(uintptr_t) alloc_ptr)
{
/* Insufficient space left; allocate another page plus one extra
page to reduce number of mmap calls. */
caddr_t page;
size_t nup = (n + GLRO(dl_pagesize) - 1) & ~(GLRO(dl_pagesize) - 1);
if (__glibc_unlikely (nup == 0 && n != 0))
return NULL;
nup += GLRO(dl_pagesize);
page = __mmap (0, nup, PROT_READ|PROT_WRITE,
MAP_ANON|MAP_PRIVATE, -1, 0);
if (page == MAP_FAILED)
return NULL;
__set_vma_name (page, nup, " glibc: loader malloc");
if (page != alloc_end)
alloc_ptr = page;
alloc_end = page + nup;
}
alloc_last_block = (void *) alloc_ptr;
alloc_ptr += n;
return alloc_last_block;
}
/* We use this function occasionally since the real implementation may
be optimized when it can assume the memory it returns already is
set to NUL. */
void *
__minimal_calloc (size_t nmemb, size_t size)
{
/* New memory from the trivial malloc above is always already cleared.
(We make sure that's true in the rare occasion it might not be,
by clearing memory in free, below.) */
size_t bytes = nmemb * size;
#define HALF_SIZE_T (((size_t) 1) << (8 * sizeof (size_t) / 2))
if (__builtin_expect ((nmemb | size) >= HALF_SIZE_T, 0)
&& size != 0 && bytes / size != nmemb)
return NULL;
return malloc (bytes);
}
/* This will rarely be called. */
void
__minimal_free (void *ptr)
{
/* We can free only the last block allocated. */
if (ptr == alloc_last_block)
{
/* Since this is rare, we clear the freed block here
so that calloc can presume malloc returns cleared memory. */
memset (alloc_last_block, '\0', alloc_ptr - alloc_last_block);
alloc_ptr = alloc_last_block;
}
}
/* This is only called with the most recent block returned by malloc. */
void *
__minimal_realloc (void *ptr, size_t n)
{
if (ptr == NULL)
return malloc (n);
assert (ptr == alloc_last_block);
size_t old_size = alloc_ptr - alloc_last_block;
alloc_ptr = alloc_last_block;
void *new = malloc (n);
return new != ptr ? memcpy (new, ptr, old_size) : new;
}
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