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--- libmalloc/libmalloc-715.120.13/src/early_malloc.c
+++ libmalloc/libmalloc-521.100.59/src/early_malloc.c
@@ -69,7 +69,7 @@
 
 static_assert(CHAR_BIT == 8, "CHAR_BIT is 8");
 static_assert(powerof2(MFM_ALLOC_SIZE_MAX), "MFM_ALLOC_SIZE_MAX is a power of 2");
-static_assert(powerof2(MFM_BLOCK_SIZE_MAX), "MFM_BLOCK_SIZE_MAX is a power of 2");
+static_assert(powerof2(MFM_BLOCK_SIZE_MAX), "MFM_ALLOC_SIZE_MAX is a power of 2");
 
 #if !MALLOC_TARGET_EXCLAVES
 #define MFM_INTERNAL_CRASH(code, msg)  ({ \
@@ -95,7 +95,7 @@
 	void *__ptrauth(ptrauth_key_process_dependent_data, true,
 			ptrauth_string_discriminator("mfmb_next"),
 			"authenticates-null-values")
-							mfmb_next;
+	                        mfmb_next;
 #else
 	uint64_t                mfmb_next;
 #endif
@@ -109,9 +109,9 @@
 	size_t                  mfm_bump_hwm;
 	size_t                  mfm_alloc_count;
 	struct mfm_block        mfm_freelist[MFM_SIZE_CLASSES];
-#if MALLOC_TARGET_EXCLAVES || MALLOC_TARGET_EXCLAVES_INTROSPECTOR
+#if MALLOC_TARGET_EXCLAVES
 	plat_map_t              mfm_map;
-#endif // MALLOC_TARGET_EXCLAVES || MALLOC_TARGET_EXCLAVES_INTROSPECTOR
+#endif // MALLOC_TARGET_EXCLAVES
 };
 
 struct mfm_arena {
@@ -158,6 +158,7 @@
 
 static struct mfm_arena    *mfm_arena;
 
+
 #pragma mark validation and helper functions
 
 /*!
@@ -530,7 +531,6 @@
 #endif
 }
 
-
 /*!
  * @function __mfm_block_insert_head()
  *
@@ -544,18 +544,15 @@
 	struct mfm_block       *blk)
 {
 	uint64_t head, offs, next;
-	struct mfm_block *next_blk;
 
 	head = __mfm_block_offset(arena, hblk);
 	next = __mfm_block_next(hblk);
 	offs = __mfm_block_offset(arena, blk);
-	next_blk = &arena->mfm_base[next];
-
 
 	blk->mfmb_prev = head;
 	__mfm_block_set_next(blk, next);
 	__mfm_block_set_next(hblk, offs);
-	next_blk->mfmb_prev = offs;
+	arena->mfm_base[next].mfmb_prev = offs;
 }
 
 /*!
@@ -568,15 +565,11 @@
 __mfm_block_remove(struct mfm_arena *arena, struct mfm_block *blk)
 {
 	uint64_t next, prev;
-	struct mfm_block *next_blk, *prev_blk;
-
 
 	next = __mfm_block_next(blk);
 	prev = blk->mfmb_prev;
-	next_blk = &arena->mfm_base[next];
-	prev_blk = &arena->mfm_base[prev];
-	next_blk->mfmb_prev = prev;
-	__mfm_block_set_next(prev_blk, next);
+	arena->mfm_base[next].mfmb_prev = prev;
+	__mfm_block_set_next(&arena->mfm_base[prev], next);
 	__builtin_bzero(blk, sizeof(struct mfm_block));
 }
 
@@ -642,28 +635,49 @@
 mfm_initialize(void)
 {
 	struct mfm_arena *arena;
-	int debug_flags;
 #if MALLOC_TARGET_EXCLAVES
 	plat_map_t map = {0};
-	debug_flags = MALLOC_NO_POPULATE;
+#endif // MALLOC_TARGET_EXCLAVES
+
+	// FIXME: rdar://115739995
+	// On exclaves, we initialize the early allocator first, so probe addresses
+	// above the reserved 4GB region to map it. This will block the subsequent
+	// xzone data/pointer regions from landing in the reserved region as well.
+	// Note that we cannot exhaustively map the reserved region because the
+	// PMM may run out of untyped memory, and on ASAN, the shadow already
+	// occupies the reserved region
+#if MALLOC_TARGET_EXCLAVES
+#if !__LIBLIBC_F_ASAN_INSTRUMENTATION
+	arena = NULL;
+	for (uintptr_t probe_addr = GiB(4); !arena; probe_addr += MFM_ARENA_SIZE) {
+		arena = mvm_allocate_plat(probe_addr, MFM_ARENA_SIZE, 0,
+				VM_FLAGS_FIXED, DISABLE_ASLR | MALLOC_NO_POPULATE,
+				VM_MEMORY_MALLOC, mvm_plat_map(map));
+	}
 #else
-	int alloc_flags = 0;
-	debug_flags = DISABLE_ASLR | MALLOC_ADD_GUARD_PAGE_FLAGS;
+	arena = mvm_allocate_pages_plat(MFM_ARENA_SIZE, 0,
+			DISABLE_ASLR | MALLOC_NO_POPULATE, VM_MEMORY_MALLOC,
+			mvm_plat_map(map));
+#endif // !__LIBLIBC_F_ASAN_INSTRUMENTATION
+#else
+	/* this is called early, which means the address space _does_ have 8M */
+	arena = mvm_allocate_pages_plat(MFM_ARENA_SIZE, 0,
+			DISABLE_ASLR | MALLOC_ADD_GUARD_PAGE_FLAGS, VM_MEMORY_MALLOC,
+			NULL);
 #endif // MALLOC_TARGET_EXCLAVES
 
-
-	/* this is called early, which means the address space _does_ have 8M */
-	arena = mvm_allocate_pages_plat(MFM_ARENA_SIZE, 0, debug_flags,
-			VM_MEMORY_MALLOC, mvm_plat_map(map));
 	if (arena == NULL) {
 		MFM_INTERNAL_CRASH(arena, "failed to allocate memory");
 	}
 
 #if MALLOC_TARGET_EXCLAVES
 	/* populate the header up to the block storage */
-	mvm_madvise_plat(arena,
-			roundup(offsetof(struct mfm_arena, mfm_blocks), PAGE_SIZE),
-			MADV_FAULTABLE, MALLOC_ABORT_ON_ERROR, mvm_plat_map(map));
+	const uintptr_t addr = (uintptr_t)mvm_allocate_plat((uintptr_t)arena,
+			roundup(offsetof(struct mfm_arena, mfm_blocks), PAGE_SIZE), 0,
+			VM_FLAGS_FIXED, 0, 0, mvm_plat_map(map));
+	if (addr != (uintptr_t)arena) {
+		MFM_INTERNAL_CRASH(addr, "populate of header failed");
+	}
 
 	arena->mfm_header.mfm_map = map;
 #else
@@ -673,8 +687,7 @@
 	 * originally because the kernel would have placed it in the heap range */
 	mach_vm_address_t vm_addr = (mach_vm_address_t)arena;
 	mach_vm_size_t vm_size = (mach_vm_size_t)MFM_ARENA_SIZE;
-	alloc_flags |= VM_FLAGS_OVERWRITE | VM_MAKE_TAG(VM_MEMORY_MALLOC_TINY);
-
+	int alloc_flags = VM_FLAGS_OVERWRITE | VM_MAKE_TAG(VM_MEMORY_MALLOC_TINY);
 	kern_return_t kr = mach_vm_map(mach_task_self(), &vm_addr, vm_size,
 			/* mask */ 0, alloc_flags, MEMORY_OBJECT_NULL, /* offset */ 0,
 			/* copy */ false, VM_PROT_DEFAULT, VM_PROT_ALL, VM_INHERIT_DEFAULT);
@@ -713,7 +726,6 @@
 	struct mfm_arena *arena = os_atomic_load(&mfm_arena, dependency);
 	size_t index;
 
-
 	if (!__mfm_address_owned(arena, ptr)) {
 		return 0ul;
 	}
@@ -763,7 +775,7 @@
 			if (blk_size > size) {
 				__mfm_block_mark_start(arena, blk_index + size);
 				__mfm_free_block(arena, blk_index + size,
-					blk_size - size);
+				    blk_size - size);
 			}
 
 			__mfm_block_mark_allocated(arena, blk_index, size);
@@ -793,9 +805,12 @@
 			const uintptr_t end = roundup((uintptr_t)ptr + alloc_size, PAGE_SIZE);
 			const size_t bytes = end - begin;
 			if (bytes) {
-				mvm_madvise_plat((void*)begin, bytes, MADV_FAULTABLE,
-						MALLOC_ABORT_ON_ERROR,
+				const uintptr_t addr = (uintptr_t)mvm_allocate_plat(begin,
+						bytes, 0, VM_FLAGS_FIXED, 0, 0,
 						mvm_plat_map(arena->mfm_header.mfm_map));
+				if (addr != begin) {
+					MFM_INTERNAL_CRASH(ptr, "populate of pages failed");
+				}
 			}
 #endif
 
@@ -811,7 +826,6 @@
 #endif
 	__mfm_unlock(arena);
 
-
 	return ptr;
 }
 
@@ -820,23 +834,20 @@
 {
 	struct mfm_arena *arena = os_atomic_load(&mfm_arena, dependency);
 	size_t index, size;
-	void *addr = ptr;
 
 #if MFM_TRACE
 	dprintf(STDERR_FILENO, "{ -1, %p },\n", ptr);
 #endif
 
-
-	if (!__mfm_address_owned(arena, addr)) {
+	if (!__mfm_address_owned(arena, ptr)) {
 		MFM_INTERNAL_CRASH(ptr, "not MFM owned");
 	}
 
-	index = __mfm_block_index(arena, addr);
+	index = __mfm_block_index(arena, ptr);
 	if (!__mfm_block_is_allocated(arena, index)) {
 		MFM_CLIENT_CRASH(ptr, "not an allocated block");
 	}
 	size = __mfm_block_size(arena, index);
-
 
 	bzero(ptr, MFM_QUANTUM * size);
 
@@ -863,7 +874,7 @@
 	}
 
 	if (index + size < arena->mfmh_bump &&
-			!__mfm_block_is_allocated(arena, index + size)) {
+	    !__mfm_block_is_allocated(arena, index + size)) {
 		size_t next  = index + size;
 		size_t nsize = __mfm_block_size(arena, next);
 
@@ -924,7 +935,7 @@
 			size_t size  = __mfm_block_size(arena, index);
 
 			P("  [%p, %p) size=%zd\n",
-					blk, blk + size, size * MFM_QUANTUM);
+			    blk, blk + size, size * MFM_QUANTUM);
 		}
 	}
 	P("\n");