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Date: Mon, 8 Jun 2020 23:50:10 -0400
From: Rich Felker <dalias@libc.org>
To: musl@lists.openwall.com
Message-ID: <20200609035010.GE1079@brightrain.aerifal.cx>
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Content-Type: multipart/mixed; boundary="BOmey7/79ja+7F5w"
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User-Agent: Mutt/1.5.21 (2010-09-15)
Subject: [musl] mallocng switchover - opportunity to test


--BOmey7/79ja+7F5w
Content-Type: text/plain; charset=us-ascii
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I just pushed a series of changes in preparation for upstreaming
mallocng. Before it's actually imported, it can be tested by
performing the following simple 4 steps:

1. mkdir src/malloc/mallocng
2. echo "MALLOC_DIR = mallocng" >> config.mak
3. Dropping the attached files into src/malloc/mallocng
4. Symlinking or copying meta.h, malloc.c, realloc.c, free.c,
   malloc_usable_size.c, and aligned_alloc.c from mallocng source dir
   to src/malloc/mallocng. (You can also include dump.c if desired.)

This produces a near-fully-integrated malloc, including support for
reclaim_gaps donation from ldso. The only functionality missing, which
I expect to flesh out before actual import, is handling of the case of
incomplete malloc replacement by interposition (__malloc_replaced!=0).

Please report any problems encountered.

Rich

--BOmey7/79ja+7F5w
Content-Type: text/plain; charset=us-ascii
Content-Disposition: attachment; filename="glue.h"

#ifndef MALLOC_GLUE_H
#define MALLOC_GLUE_H

#include <stdint.h>
#include <sys/mman.h>
#include <pthread.h>
#include <unistd.h>
#include <elf.h>
#include <string.h>
#include "atomic.h"
#include "syscall.h"
#include "libc.h"
#include "lock.h"

// use macros to appropriately namespace these.
#define size_classes __malloc_size_classes
#define ctx __malloc_context
#define alloc_meta __malloc_alloc_meta

#define dump_heap __dump_heap

#if USE_REAL_ASSERT
#include <assert.h>
#else
#undef assert
#define assert(x) do { if (!(x)) a_crash(); } while(0)
#endif

#define brk(p) ((uintptr_t)__syscall(SYS_brk, p))

#define mmap __mmap
#define madvise __madvise
#define mremap __mremap

#ifndef a_clz_32
#define a_clz_32 a_clz_32
static inline int a_clz_32(uint32_t x)
{
#ifdef __GNUC__
	return __builtin_clz(x);
#else
	x--;
	x |= x >> 1;
	x |= x >> 2;
	x |= x >> 4;
	x |= x >> 8;
	x |= x >> 16;
	x++;
	return 31-a_ctz_32(x);
#endif
}
#endif

static inline uint64_t get_random_secret()
{
	uint64_t secret = (uintptr_t)&secret * 1103515245;
	for (size_t i=0; libc.auxv[i]; i+=2)
		if (libc.auxv[i]==AT_RANDOM)
			memcpy(&secret, (char *)libc.auxv[i+1], sizeof secret);
	return secret;
}

#ifndef PAGESIZE
#define PAGESIZE PAGE_SIZE
#endif

static inline size_t get_page_size()
{
	return PAGESIZE;
}

// no portable "is multithreaded" predicate so assume true
#define MT (libc.need_locks)

#define RDLOCK_IS_EXCLUSIVE 1

__attribute__((__visibility__("hidden")))
extern int __malloc_lock[1];

#define LOCK_OBJ_DEF \
int __malloc_lock[1];

static inline void rdlock()
{
	if (MT) LOCK(__malloc_lock);
}
static inline void wrlock()
{
	if (MT) LOCK(__malloc_lock);
}
static inline void unlock()
{
	UNLOCK(__malloc_lock);
}
static inline void upgradelock()
{
}

#endif

--BOmey7/79ja+7F5w
Content-Type: text/plain; charset=us-ascii
Content-Disposition: attachment; filename="donate.c"

#include <stdlib.h>
#include <stdint.h>
#include <limits.h>
#include <string.h>
#include <sys/mman.h>
#include <errno.h>

#include "meta.h"

static void donate(unsigned char *base, size_t len)
{
	uintptr_t a = (uintptr_t)base;
	uintptr_t b = a + len;
	a += -a & (UNIT-1);
	b -= b & (UNIT-1);
	memset(base, 0, len);
	for (int sc=47; sc>0 && b>a; sc-=4) {
		if (b-a < (size_classes[sc]+1)*UNIT) continue;
		struct meta *m = alloc_meta();
		m->avail_mask = 0;
		m->freed_mask = 1;
		m->mem = (void *)a;
		m->mem->meta = m;
		m->last_idx = 0;
		m->freeable = 0;
		m->sizeclass = sc;
		m->maplen = 0;
		*((unsigned char *)m->mem+UNIT-4) = 0;
		*((unsigned char *)m->mem+UNIT-3) = 255;
		m->mem->storage[size_classes[sc]*UNIT-4] = 0;
		queue(&ctx.active[sc], m);
		a += (size_classes[sc]+1)*UNIT;
	}
}

void __malloc_donate(char *start, char *end)
{
	donate((void *)start, end-start);
}

--BOmey7/79ja+7F5w
Content-Type: text/plain; charset=us-ascii
Content-Disposition: attachment; filename="replaced.c"

#include "meta.h"

int __malloc_replaced;

--BOmey7/79ja+7F5w--