diff --git a/include/mcheck.h b/include/mcheck.h
index 8883c3d53e..5ad7cd1313 100644
--- a/include/mcheck.h
+++ b/include/mcheck.h
@@ -3,9 +3,5 @@
 #include <malloc/mcheck.h>
 
 # ifndef _ISOMAC
-
-libc_hidden_proto (mcheck)
-libc_hidden_proto (mcheck_check_all)
-
 # endif /* !_ISOMAC */
 #endif
diff --git a/malloc/Makefile b/malloc/Makefile
index 86228b101d..b1c8e3c9e0 100644
--- a/malloc/Makefile
+++ b/malloc/Makefile
@@ -90,9 +90,6 @@ tests-exclude-mcheck = tst-mallocstate \
 	tst-malloc-thread-fail \
 	tst-malloc-usable-tunables \
 	tst-malloc_info \
-	tst-memalign \
-	tst-posix_memalign \
-	tst-posix-realloc \
 	tst-compathooks-off tst-compathooks-on
 
 tests-mcheck = $(filter-out $(tests-exclude-mcheck), $(tests))
diff --git a/malloc/hooks.c b/malloc/hooks.c
index f0adcd9308..04a909b52a 100644
--- a/malloc/hooks.c
+++ b/malloc/hooks.c
@@ -59,7 +59,6 @@ generic_hook_ini (void)
   if (hook != NULL)
     (*hook)();
 #endif
-  __malloc_initialized = 1;
 }
 
 static void *
diff --git a/malloc/malloc-debug.c b/malloc/malloc-debug.c
index 1c80c33f43..daf48e0633 100644
--- a/malloc/malloc-debug.c
+++ b/malloc/malloc-debug.c
@@ -43,6 +43,35 @@ DEBUG_FN(valloc);
 DEBUG_FN(pvalloc);
 DEBUG_FN(calloc);
 
+static bool malloc_called;
+
+enum malloc_debug_hooks
+{
+  MALLOC_NONE_HOOK = 0,
+  MALLOC_MCHECK_HOOK = 1 << 0, /* mcheck()  */
+};
+static unsigned __malloc_debugging_hooks;
+
+static __always_inline bool
+__is_malloc_debug_enabled (enum malloc_debug_hooks flag)
+{
+  return __malloc_debugging_hooks & flag;
+}
+
+static __always_inline void
+__malloc_debug_enable (enum malloc_debug_hooks flag)
+{
+  __malloc_debugging_hooks |= flag;
+}
+
+static __always_inline void
+__malloc_debug_disable (enum malloc_debug_hooks flag)
+{
+  __malloc_debugging_hooks &= ~flag;
+}
+
+#include "mcheck.c"
+
 extern void (*__free_hook) (void *, const void *);
 compat_symbol_reference (libc, __free_hook, __free_hook, GLIBC_2_0);
 extern void * (*__malloc_hook) (size_t, const void *);
@@ -63,7 +92,19 @@ __debug_malloc (size_t bytes)
   if (__builtin_expect (hook != NULL, 0))
     return (*hook)(bytes, RETURN_ADDRESS (0));
 
-  return __libc_malloc (bytes);
+  malloc_called = true;
+
+  void *victim = NULL;
+  size_t orig_bytes = bytes;
+  if (!__is_malloc_debug_enabled (MALLOC_MCHECK_HOOK)
+      || !malloc_mcheck_before (&bytes, &victim))
+    {
+      victim = __libc_malloc (bytes);
+    }
+  if (__is_malloc_debug_enabled (MALLOC_MCHECK_HOOK) && victim != NULL)
+    victim = malloc_mcheck_after (victim, orig_bytes);
+
+  return victim;
 }
 strong_alias (__debug_malloc, malloc)
 
@@ -76,6 +117,10 @@ __debug_free (void *mem)
       (*hook)(mem, RETURN_ADDRESS (0));
       return;
     }
+
+  if (__is_malloc_debug_enabled (MALLOC_MCHECK_HOOK))
+    mem = free_mcheck (mem);
+
   __libc_free (mem);
 }
 strong_alias (__debug_free, free)
@@ -88,7 +133,21 @@ __debug_realloc (void *oldmem, size_t bytes)
   if (__builtin_expect (hook != NULL, 0))
     return (*hook)(oldmem, bytes, RETURN_ADDRESS (0));
 
-  return __libc_realloc (oldmem, bytes);
+  malloc_called = true;
+
+  size_t orig_bytes = bytes, oldsize = 0;
+  void *victim = NULL;
+
+  if (!__is_malloc_debug_enabled (MALLOC_MCHECK_HOOK)
+      || !realloc_mcheck_before (&oldmem, &bytes, &oldsize, &victim))
+    {
+      victim = __libc_realloc (oldmem, bytes);
+    }
+  if (__is_malloc_debug_enabled (MALLOC_MCHECK_HOOK) && victim != NULL)
+    victim = realloc_mcheck_after (victim, oldmem, orig_bytes,
+				   oldsize);
+
+  return victim;
 }
 strong_alias (__debug_realloc, realloc)
 
@@ -100,7 +159,20 @@ _mid_memalign (size_t alignment, size_t bytes, const void *address)
   if (__builtin_expect (hook != NULL, 0))
     return (*hook)(alignment, bytes, address);
 
-  return __libc_memalign (alignment, bytes);
+  malloc_called = true;
+
+  void *victim = NULL;
+  size_t orig_bytes = bytes;
+
+  if (!__is_malloc_debug_enabled (MALLOC_MCHECK_HOOK)
+      || !memalign_mcheck_before (alignment, &bytes, &victim))
+    {
+      victim = __libc_memalign (alignment, bytes);
+    }
+  if (__is_malloc_debug_enabled (MALLOC_MCHECK_HOOK) && victim != NULL)
+    victim = memalign_mcheck_after (victim, alignment, orig_bytes);
+
+  return victim;
 }
 
 static void *
@@ -165,17 +237,17 @@ strong_alias (__debug_posix_memalign, posix_memalign)
 static void *
 __debug_calloc (size_t nmemb, size_t size)
 {
+  size_t bytes;
+
+  if (__glibc_unlikely (__builtin_mul_overflow (nmemb, size, &bytes)))
+    {
+      errno = ENOMEM;
+      return NULL;
+    }
+
   void *(*hook) (size_t, const void *) = atomic_forced_read (__malloc_hook);
   if (__builtin_expect (hook != NULL, 0))
     {
-      size_t bytes;
-
-      if (__glibc_unlikely (__builtin_mul_overflow (nmemb, size, &bytes)))
-	{
-	  errno = ENOMEM;
-	  return NULL;
-	}
-
       void *mem = (*hook)(bytes, RETURN_ADDRESS (0));
 
       if (mem != NULL)
@@ -184,6 +256,22 @@ __debug_calloc (size_t nmemb, size_t size)
       return mem;
     }
 
-  return __libc_calloc (nmemb, size);
+  malloc_called = true;
+
+  size_t orig_bytes = bytes;
+  void *victim = NULL;
+
+  if (!__is_malloc_debug_enabled (MALLOC_MCHECK_HOOK)
+      || !malloc_mcheck_before (&bytes, &victim))
+    {
+      victim = __libc_malloc (bytes);
+    }
+  if (victim != NULL)
+    {
+      if (__is_malloc_debug_enabled (MALLOC_MCHECK_HOOK))
+	victim = malloc_mcheck_after (victim, orig_bytes);
+      memset (victim, 0, orig_bytes);
+    }
+  return victim;
 }
 strong_alias (__debug_calloc, calloc)
diff --git a/malloc/mcheck-impl.c b/malloc/mcheck-impl.c
new file mode 100644
index 0000000000..9d6451f738
--- /dev/null
+++ b/malloc/mcheck-impl.c
@@ -0,0 +1,406 @@
+/* mcheck debugging hooks for malloc.
+   Copyright (C) 1990-2021 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+   Written May 1989 by Mike Haertel.
+
+   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/>.  */
+
+#include <malloc-internal.h>
+#include <mcheck.h>
+#include <libintl.h>
+#include <stdint.h>
+#include <stdio.h>
+
+/* Arbitrary magical numbers.  */
+#define MAGICWORD       0xfedabeeb
+#define MAGICFREE       0xd8675309
+#define MAGICBYTE       ((char) 0xd7)
+#define MALLOCFLOOD     ((char) 0x93)
+#define FREEFLOOD       ((char) 0x95)
+
+/* Function to call when something awful happens.  */
+static void (*abortfunc) (enum mcheck_status);
+
+struct hdr
+{
+  size_t size;                  /* Exact size requested by user.  */
+  unsigned long int magic;      /* Magic number to check header integrity.  */
+  struct hdr *prev;
+  struct hdr *next;
+  void *block;                  /* Real block allocated, for memalign.  */
+  unsigned long int magic2;     /* Extra, keeps us doubleword aligned.  */
+};
+
+/* This is the beginning of the list of all memory blocks allocated.
+   It is only constructed if the pedantic testing is requested.  */
+static struct hdr *__mcheck_root;
+
+/* Nonzero if pedentic checking of all blocks is requested.  */
+static bool pedantic;
+
+#if defined _LIBC || defined STDC_HEADERS || defined USG
+# include <string.h>
+# define flood memset
+#else
+static void flood (void *, int, size_t);
+static void
+flood (void *ptr, int val, size_t size)
+{
+  char *cp = ptr;
+  while (size--)
+    *cp++ = val;
+}
+#endif
+
+static enum mcheck_status
+checkhdr (const struct hdr *hdr)
+{
+  enum mcheck_status status;
+  bool mcheck_used = __is_malloc_debug_enabled (MALLOC_MCHECK_HOOK);
+
+  if (!mcheck_used)
+    /* Maybe the mcheck used is disabled?  This happens when we find
+       an error and report it.  */
+    return MCHECK_OK;
+
+  switch (hdr->magic ^ ((uintptr_t) hdr->prev + (uintptr_t) hdr->next))
+    {
+    default:
+      status = MCHECK_HEAD;
+      break;
+    case MAGICFREE:
+      status = MCHECK_FREE;
+      break;
+    case MAGICWORD:
+      if (((char *) &hdr[1])[hdr->size] != MAGICBYTE)
+	status = MCHECK_TAIL;
+      else if ((hdr->magic2 ^ (uintptr_t) hdr->block) != MAGICWORD)
+	status = MCHECK_HEAD;
+      else
+	status = MCHECK_OK;
+      break;
+    }
+  if (status != MCHECK_OK)
+    {
+      mcheck_used = 0;
+      (*abortfunc) (status);
+      mcheck_used = 1;
+    }
+  return status;
+}
+
+static enum mcheck_status
+__mcheck_checkptr (const void *ptr)
+{
+  if (!__is_malloc_debug_enabled (MALLOC_MCHECK_HOOK))
+      return MCHECK_DISABLED;
+
+  if (ptr != NULL)
+    return checkhdr (((struct hdr *) ptr) - 1);
+
+  /* Walk through all the active blocks and test whether they were tampered
+     with.  */
+  struct hdr *runp = __mcheck_root;
+
+  /* Temporarily turn off the checks.  */
+  pedantic = false;
+
+  while (runp != NULL)
+    {
+      (void) checkhdr (runp);
+
+      runp = runp->next;
+    }
+
+  /* Turn checks on again.  */
+  pedantic = true;
+
+  return MCHECK_OK;
+}
+
+static void
+unlink_blk (struct hdr *ptr)
+{
+  if (ptr->next != NULL)
+    {
+      ptr->next->prev = ptr->prev;
+      ptr->next->magic = MAGICWORD ^ ((uintptr_t) ptr->next->prev
+                                      + (uintptr_t) ptr->next->next);
+    }
+  if (ptr->prev != NULL)
+    {
+      ptr->prev->next = ptr->next;
+      ptr->prev->magic = MAGICWORD ^ ((uintptr_t) ptr->prev->prev
+                                      + (uintptr_t) ptr->prev->next);
+    }
+  else
+    __mcheck_root = ptr->next;
+}
+
+static void
+link_blk (struct hdr *hdr)
+{
+  hdr->prev = NULL;
+  hdr->next = __mcheck_root;
+  __mcheck_root = hdr;
+  hdr->magic = MAGICWORD ^ (uintptr_t) hdr->next;
+
+  /* And the next block.  */
+  if (hdr->next != NULL)
+    {
+      hdr->next->prev = hdr;
+      hdr->next->magic = MAGICWORD ^ ((uintptr_t) hdr
+                                      + (uintptr_t) hdr->next->next);
+    }
+}
+
+static void *
+free_mcheck (void *ptr)
+{
+  if (pedantic)
+    __mcheck_checkptr (NULL);
+  if (ptr)
+    {
+      struct hdr *hdr = ((struct hdr *) ptr) - 1;
+      checkhdr (hdr);
+      hdr->magic = MAGICFREE;
+      hdr->magic2 = MAGICFREE;
+      unlink_blk (hdr);
+      hdr->prev = hdr->next = NULL;
+      flood (ptr, FREEFLOOD, hdr->size);
+      ptr = hdr->block;
+    }
+  return ptr;
+}
+
+static bool
+malloc_mcheck_before (size_t *sizep, void **victimp)
+{
+  size_t size = *sizep;
+
+  if (pedantic)
+    __mcheck_checkptr (NULL);
+
+  if (size > ~((size_t) 0) - (sizeof (struct hdr) + 1))
+    {
+      __set_errno (ENOMEM);
+      *victimp = NULL;
+      return true;
+    }
+
+  *sizep = sizeof (struct hdr) + size + 1;
+  return false;
+}
+
+static void *
+malloc_mcheck_after (void *mem, size_t size)
+{
+  struct hdr *hdr = mem;
+
+  if (hdr == NULL)
+    return NULL;
+
+  hdr->size = size;
+  link_blk (hdr);
+  hdr->block = hdr;
+  hdr->magic2 = (uintptr_t) hdr ^ MAGICWORD;
+  ((char *) &hdr[1])[size] = MAGICBYTE;
+  flood ((void *) (hdr + 1), MALLOCFLOOD, size);
+  return (void *) (hdr + 1);
+}
+
+static bool
+memalign_mcheck_before (size_t alignment, size_t *sizep, void **victimp)
+{
+  struct hdr *hdr;
+  size_t slop, size = *sizep;
+
+  /* Punt to malloc to avoid double headers.  */
+  if (alignment <= MALLOC_ALIGNMENT)
+    {
+      *victimp = __debug_malloc (size);
+      return true;
+    }
+
+  if (pedantic)
+    __mcheck_checkptr (NULL);
+
+  slop = (sizeof *hdr + alignment - 1) & - alignment;
+
+  if (size > ~((size_t) 0) - (slop + 1))
+    {
+      __set_errno (ENOMEM);
+      *victimp = NULL;
+      return true;
+    }
+
+  *sizep = slop + size + 1;
+  return false;
+}
+
+static void *
+memalign_mcheck_after (void *block, size_t alignment, size_t size)
+{
+  if (block == NULL)
+    return NULL;
+
+  /* This was served by __debug_malloc, so return as is.  */
+  if (alignment <= MALLOC_ALIGNMENT)
+    return block;
+
+  size_t slop = (sizeof (struct hdr) + alignment - 1) & - alignment;
+  struct hdr *hdr = ((struct hdr *) (block + slop)) - 1;
+
+  hdr->size = size;
+  link_blk (hdr);
+  hdr->block = (void *) block;
+  hdr->magic2 = (uintptr_t) block ^ MAGICWORD;
+  ((char *) &hdr[1])[size] = MAGICBYTE;
+  flood ((void *) (hdr + 1), MALLOCFLOOD, size);
+  return (void *) (hdr + 1);
+}
+
+static bool
+realloc_mcheck_before (void **ptrp, size_t *sizep, size_t *oldsize,
+		       void **victimp)
+{
+  size_t size = *sizep;
+  void *ptr = *ptrp;
+
+  if (ptr == NULL)
+    {
+      *victimp = __debug_malloc (size);
+      *oldsize = 0;
+      return true;
+    }
+
+  if (size == 0)
+    {
+      __debug_free (ptr);
+      *victimp = NULL;
+      return true;
+    }
+
+  if (size > ~((size_t) 0) - (sizeof (struct hdr) + 1))
+    {
+      __set_errno (ENOMEM);
+      *victimp = NULL;
+      *oldsize = 0;
+      return true;
+    }
+
+  if (pedantic)
+    __mcheck_checkptr (NULL);
+
+  struct hdr *hdr;
+  size_t osize;
+
+  /* Update the oldptr for glibc realloc.  */
+  *ptrp = hdr = ((struct hdr *) ptr) - 1;
+
+  osize = hdr->size;
+
+  checkhdr (hdr);
+  unlink_blk (hdr);
+  if (size < osize)
+    flood ((char *) ptr + size, FREEFLOOD, osize - size);
+
+  *oldsize = osize;
+  *sizep = sizeof (struct hdr) + size + 1;
+  return false;
+}
+
+static void *
+realloc_mcheck_after (void *ptr, void *oldptr, size_t size, size_t osize)
+{
+  struct hdr *hdr = ptr;
+
+  if (hdr == NULL)
+    return NULL;
+
+  /* Malloc already added the header so don't tamper with it.  */
+  if (oldptr == NULL)
+    return ptr;
+
+  hdr->size = size;
+  link_blk (hdr);
+  hdr->block = hdr;
+  hdr->magic2 = (uintptr_t) hdr ^ MAGICWORD;
+  ((char *) &hdr[1])[size] = MAGICBYTE;
+  if (size > osize)
+    flood ((char *) (hdr + 1) + osize, MALLOCFLOOD, size - osize);
+  return (void *) (hdr + 1);
+}
+
+__attribute__ ((noreturn))
+static void
+mabort (enum mcheck_status status)
+{
+  const char *msg;
+  switch (status)
+    {
+    case MCHECK_OK:
+      msg = _ ("memory is consistent, library is buggy\n");
+      break;
+    case MCHECK_HEAD:
+      msg = _ ("memory clobbered before allocated block\n");
+      break;
+    case MCHECK_TAIL:
+      msg = _ ("memory clobbered past end of allocated block\n");
+      break;
+    case MCHECK_FREE:
+      msg = _ ("block freed twice\n");
+      break;
+    default:
+      msg = _ ("bogus mcheck_status, library is buggy\n");
+      break;
+    }
+#ifdef _LIBC
+  __libc_fatal (msg);
+#else
+  fprintf (stderr, "mcheck: %s", msg);
+  fflush (stderr);
+  abort ();
+#endif
+}
+
+/* Memory barrier so that GCC does not optimize out the argument.  */
+#define malloc_opt_barrier(x) \
+  ({ __typeof (x) __x = x; __asm ("" : "+m" (__x)); __x; })
+
+static int
+__mcheck_initialize (void (*func) (enum mcheck_status), bool in_pedantic)
+{
+  abortfunc = (func != NULL) ? func : &mabort;
+
+  if (__is_malloc_debug_enabled (MALLOC_MCHECK_HOOK))
+    goto out;
+
+  /* There was a call to malloc before this initializer was called.  */
+  if (malloc_called)
+    return -1;
+
+  /* We call malloc() once here to ensure it is initialized.  */
+  void *p = malloc (0);
+  /* GCC might optimize out the malloc/free pair without a barrier.  */
+  p = malloc_opt_barrier (p);
+  free (p);
+  /* FALLTHROUGH */
+  __malloc_debug_enable (MALLOC_MCHECK_HOOK);
+
+out:
+  pedantic = in_pedantic;
+  return 0;
+}
diff --git a/malloc/mcheck.c b/malloc/mcheck.c
index b46b9b26bf..74c20ffe25 100644
--- a/malloc/mcheck.c
+++ b/malloc/mcheck.c
@@ -1,4 +1,4 @@
-/* Standard debugging hooks for `malloc'.
+/* The mcheck() interface.
    Copyright (C) 1990-2021 Free Software Foundation, Inc.
    This file is part of the GNU C Library.
    Written May 1989 by Mike Haertel.
@@ -17,401 +17,46 @@
    License along with the GNU C Library; if not, see
    <https://www.gnu.org/licenses/>.  */
 
-#ifndef _MALLOC_INTERNAL
-# define _MALLOC_INTERNAL
-# include <malloc.h>
-# include <mcheck.h>
-# include <stdint.h>
-# include <stdio.h>
-# include <libintl.h>
-# include <errno.h>
-# include <malloc-internal.h>
-#endif
-
-/* Old hook values.  */
-static void (*old_free_hook)(void *ptr, const void *);
-static void *(*old_malloc_hook) (size_t size, const void *);
-static void *(*old_memalign_hook) (size_t alignment, size_t size,
-				   const void *);
-static void *(*old_realloc_hook) (void *ptr, size_t size,
-				  const void *);
-
-/* Function to call when something awful happens.  */
-static void (*abortfunc) (enum mcheck_status);
-
-/* Arbitrary magical numbers.  */
-#define MAGICWORD       0xfedabeeb
-#define MAGICFREE       0xd8675309
-#define MAGICBYTE       ((char) 0xd7)
-#define MALLOCFLOOD     ((char) 0x93)
-#define FREEFLOOD       ((char) 0x95)
-
-struct hdr
-{
-  size_t size;                  /* Exact size requested by user.  */
-  unsigned long int magic;      /* Magic number to check header integrity.  */
-  struct hdr *prev;
-  struct hdr *next;
-  void *block;                  /* Real block allocated, for memalign.  */
-  unsigned long int magic2;     /* Extra, keeps us doubleword aligned.  */
-};
-
-/* This is the beginning of the list of all memory blocks allocated.
-   It is only constructed if the pedantic testing is requested.  */
-static struct hdr *root;
-
-static int mcheck_used;
-
-/* Nonzero if pedentic checking of all blocks is requested.  */
-static int pedantic;
-
-#if defined _LIBC || defined STDC_HEADERS || defined USG
-# include <string.h>
-# define flood memset
+#if !IS_IN (libc)
+# include "mcheck-impl.c"
 #else
-static void flood (void *, int, size_t);
-static void
-flood (void *ptr, int val, size_t size)
-{
-  char *cp = ptr;
-  while (size--)
-    *cp++ = val;
-}
+# include <mcheck.h>
 #endif
 
-static enum mcheck_status
-checkhdr (const struct hdr *hdr)
-{
-  enum mcheck_status status;
-
-  if (!mcheck_used)
-    /* Maybe the mcheck used is disabled?  This happens when we find
-       an error and report it.  */
-    return MCHECK_OK;
-
-  switch (hdr->magic ^ ((uintptr_t) hdr->prev + (uintptr_t) hdr->next))
-    {
-    default:
-      status = MCHECK_HEAD;
-      break;
-    case MAGICFREE:
-      status = MCHECK_FREE;
-      break;
-    case MAGICWORD:
-      if (((char *) &hdr[1])[hdr->size] != MAGICBYTE)
-        status = MCHECK_TAIL;
-      else if ((hdr->magic2 ^ (uintptr_t) hdr->block) != MAGICWORD)
-        status = MCHECK_HEAD;
-      else
-        status = MCHECK_OK;
-      break;
-    }
-  if (status != MCHECK_OK)
-    {
-      mcheck_used = 0;
-      (*abortfunc) (status);
-      mcheck_used = 1;
-    }
-  return status;
-}
-
 void
 mcheck_check_all (void)
 {
-  /* Walk through all the active blocks and test whether they were tampered
-     with.  */
-  struct hdr *runp = root;
-
-  /* Temporarily turn off the checks.  */
-  pedantic = 0;
-
-  while (runp != NULL)
-    {
-      (void) checkhdr (runp);
-
-      runp = runp->next;
-    }
-
-  /* Turn checks on again.  */
-  pedantic = 1;
-}
-#ifdef _LIBC
-libc_hidden_def (mcheck_check_all)
+#if !IS_IN (libc)
+  __mcheck_checkptr (NULL);
 #endif
-
-static void
-unlink_blk (struct hdr *ptr)
-{
-  if (ptr->next != NULL)
-    {
-      ptr->next->prev = ptr->prev;
-      ptr->next->magic = MAGICWORD ^ ((uintptr_t) ptr->next->prev
-                                      + (uintptr_t) ptr->next->next);
-    }
-  if (ptr->prev != NULL)
-    {
-      ptr->prev->next = ptr->next;
-      ptr->prev->magic = MAGICWORD ^ ((uintptr_t) ptr->prev->prev
-                                      + (uintptr_t) ptr->prev->next);
-    }
-  else
-    root = ptr->next;
-}
-
-static void
-link_blk (struct hdr *hdr)
-{
-  hdr->prev = NULL;
-  hdr->next = root;
-  root = hdr;
-  hdr->magic = MAGICWORD ^ (uintptr_t) hdr->next;
-
-  /* And the next block.  */
-  if (hdr->next != NULL)
-    {
-      hdr->next->prev = hdr;
-      hdr->next->magic = MAGICWORD ^ ((uintptr_t) hdr
-                                      + (uintptr_t) hdr->next->next);
-    }
 }
-static void
-freehook (void *ptr, const void *caller)
-{
-  if (pedantic)
-    mcheck_check_all ();
-  if (ptr)
-    {
-      struct hdr *hdr = ((struct hdr *) ptr) - 1;
-      checkhdr (hdr);
-      hdr->magic = MAGICFREE;
-      hdr->magic2 = MAGICFREE;
-      unlink_blk (hdr);
-      hdr->prev = hdr->next = NULL;
-      flood (ptr, FREEFLOOD, hdr->size);
-      ptr = hdr->block;
-    }
-  __free_hook = old_free_hook;
-  if (old_free_hook != NULL)
-    (*old_free_hook)(ptr, caller);
-  else
-    free (ptr);
-  __free_hook = freehook;
-}
-
-static void *
-mallochook (size_t size, const void *caller)
-{
-  struct hdr *hdr;
-
-  if (pedantic)
-    mcheck_check_all ();
-
-  if (size > ~((size_t) 0) - (sizeof (struct hdr) + 1))
-    {
-      __set_errno (ENOMEM);
-      return NULL;
-    }
-
-  __malloc_hook = old_malloc_hook;
-  if (old_malloc_hook != NULL)
-    hdr = (struct hdr *) (*old_malloc_hook)(sizeof (struct hdr) + size + 1,
-                                            caller);
-  else
-    hdr = (struct hdr *) malloc (sizeof (struct hdr) + size + 1);
-  __malloc_hook = mallochook;
-  if (hdr == NULL)
-    return NULL;
-
-  hdr->size = size;
-  link_blk (hdr);
-  hdr->block = hdr;
-  hdr->magic2 = (uintptr_t) hdr ^ MAGICWORD;
-  ((char *) &hdr[1])[size] = MAGICBYTE;
-  flood ((void *) (hdr + 1), MALLOCFLOOD, size);
-  return (void *) (hdr + 1);
-}
-
-static void *
-memalignhook (size_t alignment, size_t size,
-              const void *caller)
-{
-  struct hdr *hdr;
-  size_t slop;
-  char *block;
-
-  if (pedantic)
-    mcheck_check_all ();
-
-  slop = (sizeof *hdr + alignment - 1) & - alignment;
-
-  if (size > ~((size_t) 0) - (slop + 1))
-    {
-      __set_errno (ENOMEM);
-      return NULL;
-    }
-
-  __memalign_hook = old_memalign_hook;
-  if (old_memalign_hook != NULL)
-    block = (*old_memalign_hook)(alignment, slop + size + 1, caller);
-  else
-    block = memalign (alignment, slop + size + 1);
-  __memalign_hook = memalignhook;
-  if (block == NULL)
-    return NULL;
-
-  hdr = ((struct hdr *) (block + slop)) - 1;
-
-  hdr->size = size;
-  link_blk (hdr);
-  hdr->block = (void *) block;
-  hdr->magic2 = (uintptr_t) block ^ MAGICWORD;
-  ((char *) &hdr[1])[size] = MAGICBYTE;
-  flood ((void *) (hdr + 1), MALLOCFLOOD, size);
-  return (void *) (hdr + 1);
-}
-
-static void *
-reallochook (void *ptr, size_t size, const void *caller)
-{
-  if (size == 0)
-    {
-      freehook (ptr, caller);
-      return NULL;
-    }
-
-  struct hdr *hdr;
-  size_t osize;
-
-  if (pedantic)
-    mcheck_check_all ();
-
-  if (size > ~((size_t) 0) - (sizeof (struct hdr) + 1))
-    {
-      __set_errno (ENOMEM);
-      return NULL;
-    }
-
-  if (ptr)
-    {
-      hdr = ((struct hdr *) ptr) - 1;
-      osize = hdr->size;
-
-      checkhdr (hdr);
-      unlink_blk (hdr);
-      if (size < osize)
-        flood ((char *) ptr + size, FREEFLOOD, osize - size);
-    }
-  else
-    {
-      osize = 0;
-      hdr = NULL;
-    }
-  __free_hook = old_free_hook;
-  __malloc_hook = old_malloc_hook;
-  __memalign_hook = old_memalign_hook;
-  __realloc_hook = old_realloc_hook;
-  if (old_realloc_hook != NULL)
-    hdr = (struct hdr *) (*old_realloc_hook)((void *) hdr,
-                                             sizeof (struct hdr) + size + 1,
-                                             caller);
-  else
-    hdr = (struct hdr *) realloc ((void *) hdr,
-                                  sizeof (struct hdr) + size + 1);
-  __free_hook = freehook;
-  __malloc_hook = mallochook;
-  __memalign_hook = memalignhook;
-  __realloc_hook = reallochook;
-  if (hdr == NULL)
-    return NULL;
-
-  hdr->size = size;
-  link_blk (hdr);
-  hdr->block = hdr;
-  hdr->magic2 = (uintptr_t) hdr ^ MAGICWORD;
-  ((char *) &hdr[1])[size] = MAGICBYTE;
-  if (size > osize)
-    flood ((char *) (hdr + 1) + osize, MALLOCFLOOD, size - osize);
-  return (void *) (hdr + 1);
-}
-
-__attribute__ ((noreturn))
-static void
-mabort (enum mcheck_status status)
-{
-  const char *msg;
-  switch (status)
-    {
-    case MCHECK_OK:
-      msg = _ ("memory is consistent, library is buggy\n");
-      break;
-    case MCHECK_HEAD:
-      msg = _ ("memory clobbered before allocated block\n");
-      break;
-    case MCHECK_TAIL:
-      msg = _ ("memory clobbered past end of allocated block\n");
-      break;
-    case MCHECK_FREE:
-      msg = _ ("block freed twice\n");
-      break;
-    default:
-      msg = _ ("bogus mcheck_status, library is buggy\n");
-      break;
-    }
-#ifdef _LIBC
-  __libc_fatal (msg);
-#else
-  fprintf (stderr, "mcheck: %s", msg);
-  fflush (stderr);
-  abort ();
-#endif
-}
-
-/* Memory barrier so that GCC does not optimize out the argument.  */
-#define malloc_opt_barrier(x) \
-  ({ __typeof (x) __x = x; __asm ("" : "+m" (__x)); __x; })
 
 int
 mcheck (void (*func) (enum mcheck_status))
 {
-  abortfunc = (func != NULL) ? func : &mabort;
-
-  /* These hooks may not be safely inserted if malloc is already in use.  */
-  if (__malloc_initialized <= 0 && !mcheck_used)
-    {
-      /* We call malloc() once here to ensure it is initialized.  */
-      void *p = malloc (0);
-      /* GCC might optimize out the malloc/free pair without a barrier.  */
-      p = malloc_opt_barrier (p);
-      free (p);
-
-      old_free_hook = __free_hook;
-      __free_hook = freehook;
-      old_malloc_hook = __malloc_hook;
-      __malloc_hook = mallochook;
-      old_memalign_hook = __memalign_hook;
-      __memalign_hook = memalignhook;
-      old_realloc_hook = __realloc_hook;
-      __realloc_hook = reallochook;
-      mcheck_used = 1;
-    }
-
-  return mcheck_used ? 0 : -1;
-}
-#ifdef _LIBC
-libc_hidden_def (mcheck)
+#if IS_IN (libc)
+  return -1;
+#else
+  return __mcheck_initialize (func, false);
 #endif
+}
 
 int
 mcheck_pedantic (void (*func) (enum mcheck_status))
 {
-  int res = mcheck (func);
-  if (res == 0)
-    pedantic = 1;
-  return res;
+#if IS_IN (libc)
+  return -1;
+#else
+  return __mcheck_initialize (func, true);
+#endif
 }
 
 enum mcheck_status
 mprobe (void *ptr)
 {
-  return mcheck_used ? checkhdr (((struct hdr *) ptr) - 1) : MCHECK_DISABLED;
+#if IS_IN (libc)
+  return MCHECK_DISABLED;
+#else
+  return __mcheck_checkptr (ptr);
+#endif
 }
