diff mbox series

[v5,1/8] Move malloc hooks into a compat DSO

Message ID 20210705170814.4132997-2-siddhesh@sourceware.org
State Superseded
Headers show
Series malloc hooks removal | expand

Checks

Context Check Description
dj/TryBot-apply_patch success Patch applied to master at the time it was sent

Commit Message

Siddhesh Poyarekar July 5, 2021, 5:08 p.m. UTC
Remove all malloc hook uses from core malloc functions and move it
into a new library libc_malloc_debug.so.  With this, the hooks now no
longer have any effect on the core library.

libc_malloc_debug.so is a malloc interposer that needs to be preloaded
to get hooks functionality back so that the debugging features that
depend on the hooks, i.e. malloc-check, mcheck and mtrace work again.
Without the preloaded DSO these debugging features will be nops.
These features will be ported away from hooks in subsequent patches.

Similarly, legacy applications that need hooks functionality need to
preload libc_malloc_debug.so.

Finally, static binaries will no longer be able to use malloc
debugging features since they cannot preload the debugging DSO.
---
 Makeconfig                                 |   2 +-
 NEWS                                       |   6 +
 Rules                                      |   9 +-
 catgets/Makefile                           |   4 +-
 elf/Makefile                               |  18 +-
 elf/tst-leaks1-static.c                    |   1 -
 iconvdata/Makefile                         |   3 +-
 intl/tst-gettext.sh                        |   1 +
 libio/Makefile                             |  12 +-
 localedata/Makefile                        |   3 +-
 malloc/Makefile                            |  44 +++--
 malloc/arena.c                             |   7 -
 malloc/hooks.c                             |  60 +++++--
 malloc/malloc-debug.c                      | 189 +++++++++++++++++++++
 malloc/malloc.c                            |  77 ++-------
 malloc/mcheck.c                            |   1 +
 malloc/mtrace.c                            |   1 +
 malloc/tst-compathooks-off.c               | 145 ++++++++++++++++
 malloc/tst-compathooks-on.c                |   2 +
 malloc/tst-malloc-usable-static-tunables.c |   1 -
 malloc/tst-malloc-usable-static.c          |   1 -
 malloc/tst-mtrace.sh                       |   1 +
 manual/memory.texi                         |  16 +-
 manual/tunables.texi                       |   4 +-
 misc/Makefile                              |   6 +-
 nptl/Makefile                              |   3 +-
 posix/Makefile                             |  40 +++--
 resolv/Makefile                            |   9 +-
 stdio-common/Makefile                      |  15 +-
 sysdeps/pthread/Makefile                   |   3 +-
 30 files changed, 534 insertions(+), 150 deletions(-)
 delete mode 100644 elf/tst-leaks1-static.c
 create mode 100644 malloc/malloc-debug.c
 create mode 100644 malloc/tst-compathooks-off.c
 create mode 100644 malloc/tst-compathooks-on.c
 delete mode 100644 malloc/tst-malloc-usable-static-tunables.c
 delete mode 100644 malloc/tst-malloc-usable-static.c

Comments

Florian Weimer July 6, 2021, 10:17 a.m. UTC | #1
* Siddhesh Poyarekar:

> Remove all malloc hook uses from core malloc functions and move it
> into a new library libc_malloc_debug.so.  With this, the hooks now no
> longer have any effect on the core library.

There are still a few references to libmalloc_compathooks.

> diff --git a/elf/Makefile b/elf/Makefile
> index 698a6ab985..b432e78d39 100644
> --- a/elf/Makefile
> +++ b/elf/Makefile
> @@ -156,7 +156,7 @@ $(inst_auditdir)/sotruss-lib.so: $(objpfx)sotruss-lib.so $(+force)

> @@ -1561,7 +1558,8 @@ $(objpfx)tst-nodelete-dlclose.out: $(objpfx)tst-nodelete-dlclose-dso.so \
>  				   $(objpfx)tst-nodelete-dlclose-plugin.so
>  
>  tst-env-setuid-ENV = MALLOC_CHECK_=2 MALLOC_MMAP_THRESHOLD_=4096 \
> -		     LD_HWCAP_MASK=0x1
> +		     LD_HWCAP_MASK=0x1 \
> +		     LD_PRELOAD=$(common-objpfx)/malloc/libc_malloc_debug.so

I don't think this test needs the debugging allocator, it uses getenv to
see if the environment has been scrubbed.

In general, it looks like it's time to add support for mtrace tests to
the setsuite (that is, tests-mtrace like tests-time64).

Thanks,
Florian
Siddhesh Poyarekar July 6, 2021, 1 p.m. UTC | #2
On 7/6/21 3:47 PM, Florian Weimer via Libc-alpha wrote:
> * Siddhesh Poyarekar:
> 
>> Remove all malloc hook uses from core malloc functions and move it
>> into a new library libc_malloc_debug.so.  With this, the hooks now no
>> longer have any effect on the core library.
> 
> There are still a few references to libmalloc_compathooks.

Fixed locally.

>> diff --git a/elf/Makefile b/elf/Makefile
>> index 698a6ab985..b432e78d39 100644
>> --- a/elf/Makefile
>> +++ b/elf/Makefile
>> @@ -156,7 +156,7 @@ $(inst_auditdir)/sotruss-lib.so: $(objpfx)sotruss-lib.so $(+force)
> 
>> @@ -1561,7 +1558,8 @@ $(objpfx)tst-nodelete-dlclose.out: $(objpfx)tst-nodelete-dlclose-dso.so \
>>   				   $(objpfx)tst-nodelete-dlclose-plugin.so
>>   
>>   tst-env-setuid-ENV = MALLOC_CHECK_=2 MALLOC_MMAP_THRESHOLD_=4096 \
>> -		     LD_HWCAP_MASK=0x1
>> +		     LD_HWCAP_MASK=0x1 \
>> +		     LD_PRELOAD=$(common-objpfx)/malloc/libc_malloc_debug.so
> 
> I don't think this test needs the debugging allocator, it uses getenv to
> see if the environment has been scrubbed.

You're right, it doesn't.  I'll remove that.

> In general, it looks like it's time to add support for mtrace tests to
> the setsuite (that is, tests-mtrace like tests-time64).

... or tests-mcheck/tests-malloc-check.  Would you be OK with having the 
test driver call mtrace() at all times?  Only the tests in tests-mtrace 
(which for starters we could add all tests in malloc to) will actually 
have any impact.

Thanks,
Siddhesh
Siddhesh Poyarekar July 6, 2021, 1:12 p.m. UTC | #3
On 7/6/21 6:30 PM, Siddhesh Poyarekar via Libc-alpha wrote:
>> In general, it looks like it's time to add support for mtrace tests to
>> the setsuite (that is, tests-mtrace like tests-time64).
> 
> ... or tests-mcheck/tests-malloc-check.  Would you be OK with having the 
> test driver call mtrace() at all times?  Only the tests in tests-mtrace 
> (which for starters we could add all tests in malloc to) will actually 
> have any impact.


I forgot to ask, would you like that to be part of this patchset or 
would you be OK with the testing enhancement coming in later?  Mtrace 
already has some testing coverage through tst-mtrace for example and 
other tests using mtrace.

Siddhesh
Florian Weimer July 6, 2021, 2:29 p.m. UTC | #4
* Siddhesh Poyarekar:

>> In general, it looks like it's time to add support for mtrace tests to
>> the setsuite (that is, tests-mtrace like tests-time64).
>
> ... or tests-mcheck/tests-malloc-check.  Would you be OK with having
> the test driver call mtrace() at all times?

Could we enable mtrace directly via LD_PRELOAD (or static linking),
without calling the function?

There's also the matter of not flagging potentially leaking allocations
from the test harness itself.

> I forgot to ask, would you like that to be part of this patchset or
> would you be OK with the testing enhancement coming in later?  Mtrace 
> already has some testing coverage through tst-mtrace for example and
> other tests using mtrace.

I don't have a strong preference.  Given the open questions, it's
probably best to delay the cleanup.

Thanks,
Florian
Siddhesh Poyarekar July 6, 2021, 2:40 p.m. UTC | #5
On 7/6/21 7:59 PM, Florian Weimer via Libc-alpha wrote:
> * Siddhesh Poyarekar:
> 
>>> In general, it looks like it's time to add support for mtrace tests to
>>> the setsuite (that is, tests-mtrace like tests-time64).
>>
>> ... or tests-mcheck/tests-malloc-check.  Would you be OK with having
>> the test driver call mtrace() at all times?
> 
> Could we enable mtrace directly via LD_PRELOAD (or static linking),
> without calling the function?
> 
> There's also the matter of not flagging potentially leaking allocations
> from the test harness itself.

We could link tests with an object that calls mtrace through the 
initialization hook like we do for tests-mcheck, but it will be 
equivalent to calling mtrace() in the driver.  If anything, it may end 
up getting called earlier, possibly recording dynamic linker allocations.

>> I forgot to ask, would you like that to be part of this patchset or
>> would you be OK with the testing enhancement coming in later?  Mtrace
>> already has some testing coverage through tst-mtrace for example and
>> other tests using mtrace.
> 
> I don't have a strong preference.  Given the open questions, it's
> probably best to delay the cleanup.

OK thanks.  I won't delay too long, just that I'd like it if it doesn't 
block this patchset.

Thanks,
Siddhesh
diff mbox series

Patch

diff --git a/Makeconfig b/Makeconfig
index efc7351d71..6319941ef9 100644
--- a/Makeconfig
+++ b/Makeconfig
@@ -951,7 +951,7 @@  libio-include = -I$(..)libio
 built-modules = iconvprogs iconvdata ldconfig lddlibc4 libmemusage \
 		libSegFault libpcprofile librpcsvc locale-programs \
 		memusagestat nonlib nscd extramodules libnldbl libsupport \
-		testsuite
+		testsuite libc_malloc_debug
 
 in-module = $(subst -,_,$(firstword $(libof-$(basename $(@F))) \
 				    $(libof-$(<F)) \
diff --git a/NEWS b/NEWS
index 8e72946c3f..213d790024 100644
--- a/NEWS
+++ b/NEWS
@@ -97,6 +97,12 @@  Deprecated and removed features, and other changes affecting compatibility:
   mtrace.  Similar functionality can be achieved by using conditional
   breakpoints within mtrace functions from within gdb.
 
+* Debugging features in malloc such as the MALLOC_CHECK_ environment variable
+  (or the glibc.malloc.check tunable), mtrace() and mcheck() have now been
+  disabled by default in the main C library.  Users looking to use these
+  features now need to preload a new debugging DSO libc_malloc_debug.so to get
+  this functionality back.
+
 Changes to build and runtime requirements:
 
 * On Linux, the shm_open, sem_open, and related functions now expect the
diff --git a/Rules b/Rules
index ba13598df6..b1137afe71 100644
--- a/Rules
+++ b/Rules
@@ -279,10 +279,17 @@  endif
 
 # All malloc-check tests will be run with MALLOC_CHECK_=3
 define malloc-check-ENVS
-$(1)-malloc-check-ENV = MALLOC_CHECK_=3
+$(1)-malloc-check-ENV = MALLOC_CHECK_=3 \
+			LD_PRELOAD=$(common-objpfx)/malloc/libc_malloc_debug.so
 endef
 $(foreach t,$(tests-malloc-check),$(eval $(call malloc-check-ENVS,$(t))))
 
+# mcheck tests need the debug DSO to support -lmcheck.
+define mcheck-ENVS
+$(1)-mcheck-ENV = LD_PRELOAD=$(common-objpfx)/malloc/libc_malloc_debug.so
+endef
+$(foreach t,$(tests-mcheck),$(eval $(call mcheck-ENVS,$(t))))
+
 ifneq "$(strip $(tests) $(tests-internal) $(xtests) $(test-srcs))" ""
 # These are the implicit rules for making test outputs
 # from the test programs and whatever input files are present.
diff --git a/catgets/Makefile b/catgets/Makefile
index 54da9a985f..215965b352 100644
--- a/catgets/Makefile
+++ b/catgets/Makefile
@@ -56,7 +56,9 @@  generated += tst-catgets.mtrace tst-catgets-mem.out
 
 generated-dirs += de
 
-tst-catgets-ENV = NLSPATH="$(objpfx)%l/%N.cat" LANG=de MALLOC_TRACE=$(objpfx)tst-catgets.mtrace
+tst-catgets-ENV = NLSPATH="$(objpfx)%l/%N.cat" LANG=de \
+		  MALLOC_TRACE=$(objpfx)tst-catgets.mtrace \
+		  LD_PRELOAD=$(common-objpfx)/malloc/libc_malloc_debug.so
 
 ifeq ($(run-built-tests),yes)
 # This test just checks whether the program produces any error or not.
diff --git a/elf/Makefile b/elf/Makefile
index 698a6ab985..b432e78d39 100644
--- a/elf/Makefile
+++ b/elf/Makefile
@@ -156,7 +156,7 @@  $(inst_auditdir)/sotruss-lib.so: $(objpfx)sotruss-lib.so $(+force)
 	$(do-install-program)
 endif
 
-tests-static-normal := tst-leaks1-static tst-array1-static tst-array5-static \
+tests-static-normal := tst-array1-static tst-array5-static \
 	       tst-dl-iter-static \
 	       tst-tlsalign-static tst-tlsalign-extern-static \
 	       tst-linkall-static tst-env-setuid tst-env-setuid-tunables \
@@ -242,7 +242,7 @@  endif
 tests += $(tests-execstack-$(have-z-execstack))
 ifeq ($(run-built-tests),yes)
 tests-special += $(objpfx)tst-leaks1-mem.out \
-		 $(objpfx)tst-leaks1-static-mem.out $(objpfx)noload-mem.out \
+		 $(objpfx)noload-mem.out \
 		 $(objpfx)tst-ldconfig-X.out $(objpfx)tst-rtld-help.out
 endif
 tlsmod17a-suffixes = 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
@@ -895,7 +895,8 @@  $(objpfx)noload.out: $(objpfx)testobj5.so
 $(objpfx)noload-mem.out: $(objpfx)noload.out
 	$(common-objpfx)malloc/mtrace $(objpfx)noload.mtrace > $@; \
 	$(evaluate-test)
-noload-ENV = MALLOC_TRACE=$(objpfx)noload.mtrace
+noload-ENV = MALLOC_TRACE=$(objpfx)noload.mtrace \
+	     LD_PRELOAD=$(common-objpfx)/malloc/libc_malloc_debug.so
 
 LDFLAGS-nodelete = -rdynamic
 LDFLAGS-nodelmod1.so = -Wl,--enable-new-dtags,-z,nodelete
@@ -1273,12 +1274,8 @@  $(objpfx)tst-leaks1-mem.out: $(objpfx)tst-leaks1.out
 	$(common-objpfx)malloc/mtrace $(objpfx)tst-leaks1.mtrace > $@; \
 	$(evaluate-test)
 
-$(objpfx)tst-leaks1-static-mem.out: $(objpfx)tst-leaks1-static.out
-	$(common-objpfx)malloc/mtrace $(objpfx)tst-leaks1-static.mtrace > $@; \
-	$(evaluate-test)
-
-tst-leaks1-ENV = MALLOC_TRACE=$(objpfx)tst-leaks1.mtrace
-tst-leaks1-static-ENV = MALLOC_TRACE=$(objpfx)tst-leaks1-static.mtrace
+tst-leaks1-ENV = MALLOC_TRACE=$(objpfx)tst-leaks1.mtrace \
+		 LD_PRELOAD=$(common-objpfx)/malloc/libc_malloc_debug.so
 
 $(objpfx)tst-thrlock: $(shared-thread-library)
 
@@ -1561,7 +1558,8 @@  $(objpfx)tst-nodelete-dlclose.out: $(objpfx)tst-nodelete-dlclose-dso.so \
 				   $(objpfx)tst-nodelete-dlclose-plugin.so
 
 tst-env-setuid-ENV = MALLOC_CHECK_=2 MALLOC_MMAP_THRESHOLD_=4096 \
-		     LD_HWCAP_MASK=0x1
+		     LD_HWCAP_MASK=0x1 \
+		     LD_PRELOAD=$(common-objpfx)/malloc/libc_malloc_debug.so
 
 $(objpfx)tst-debug1.out: $(objpfx)tst-debug1mod1.so
 
diff --git a/elf/tst-leaks1-static.c b/elf/tst-leaks1-static.c
deleted file mode 100644
index b956d66905..0000000000
--- a/elf/tst-leaks1-static.c
+++ /dev/null
@@ -1 +0,0 @@ 
-#include "tst-leaks1.c"
diff --git a/iconvdata/Makefile b/iconvdata/Makefile
index bb3f621b49..c216f959df 100644
--- a/iconvdata/Makefile
+++ b/iconvdata/Makefile
@@ -301,7 +301,8 @@  cpp-srcs-left := $(modules) $(generated-modules) $(libJIS-routines) \
 lib := iconvdata
 include $(patsubst %,$(..)libof-iterator.mk,$(cpp-srcs-left))
 
-tst-loading-ENV = MALLOC_TRACE=$(objpfx)tst-loading.mtrace
+tst-loading-ENV = MALLOC_TRACE=$(objpfx)tst-loading.mtrace \
+		  LD_PRELOAD=$(common-objpfx)/malloc/libc_malloc_debug.so
 $(objpfx)mtrace-tst-loading.out: $(objpfx)tst-loading.out
 	$(common-objpfx)malloc/mtrace $(objpfx)tst-loading.mtrace > $@; \
 	$(evaluate-test)
diff --git a/intl/tst-gettext.sh b/intl/tst-gettext.sh
index 77864de18c..37d9fcb80a 100755
--- a/intl/tst-gettext.sh
+++ b/intl/tst-gettext.sh
@@ -50,6 +50,7 @@  msgfmt -o ${objpfx}domaindir/existing-locale/LC_TIME/existing-time-domain.mo \
 ${test_program_prefix_before_env} \
 ${run_program_env} \
 MALLOC_TRACE=$malloc_trace \
+LD_PRELOAD=${common_objpfx}malloc/libc_malloc_debug.so \
 LOCPATH=${objpfx}localedir:${common_objpfx}localedata \
 ${test_program_prefix_after_env} \
 ${objpfx}tst-gettext > ${objpfx}tst-gettext.out ${objpfx}domaindir
diff --git a/libio/Makefile b/libio/Makefile
index 73f731e064..5336b7d595 100644
--- a/libio/Makefile
+++ b/libio/Makefile
@@ -165,10 +165,14 @@  LDFLAGS-tst-bz24228 = -Wl,--version-script=tst-bz24228.map
 
 tst_wprintf2-ARGS = "Some Text"
 
-test-fmemopen-ENV = MALLOC_TRACE=$(objpfx)test-fmemopen.mtrace
-tst-fopenloc-ENV = MALLOC_TRACE=$(objpfx)tst-fopenloc.mtrace
-tst-bz22415-ENV = MALLOC_TRACE=$(objpfx)tst-bz22415.mtrace
-tst-bz24228-ENV = MALLOC_TRACE=$(objpfx)tst-bz24228.mtrace
+test-fmemopen-ENV = MALLOC_TRACE=$(objpfx)test-fmemopen.mtrace \
+		    LD_PRELOAD=$(common-objpfx)/malloc/libc_malloc_debug.so
+tst-fopenloc-ENV = MALLOC_TRACE=$(objpfx)tst-fopenloc.mtrace \
+		   LD_PRELOAD=$(common-objpfx)/malloc/libc_malloc_debug.so
+tst-bz22415-ENV = MALLOC_TRACE=$(objpfx)tst-bz22415.mtrace \
+		  LD_PRELOAD=$(common-objpfx)/malloc/libc_malloc_debug.so
+tst-bz24228-ENV = MALLOC_TRACE=$(objpfx)tst-bz24228.mtrace \
+		  LD_PRELOAD=$(common-objpfx)/malloc/libc_malloc_debug.so
 
 generated += test-fmemopen.mtrace test-fmemopen.check
 generated += tst-fopenloc.mtrace tst-fopenloc.check
diff --git a/localedata/Makefile b/localedata/Makefile
index 14e04cd3c5..f585e0dd41 100644
--- a/localedata/Makefile
+++ b/localedata/Makefile
@@ -456,7 +456,8 @@  $(INSTALL-SUPPORTED-LOCALE-FILES): install-locales-dir
 tst-setlocale-ENV = LC_ALL=ja_JP.EUC-JP
 tst-wctype-ENV = LC_ALL=ja_JP.EUC-JP
 
-tst-leaks-ENV = MALLOC_TRACE=$(objpfx)tst-leaks.mtrace
+tst-leaks-ENV = MALLOC_TRACE=$(objpfx)tst-leaks.mtrace \
+		LD_PRELOAD=$(common-objpfx)/malloc/libc_malloc_debug.so
 $(objpfx)mtrace-tst-leaks.out: $(objpfx)tst-leaks.out
 	$(common-objpfx)malloc/mtrace $(objpfx)tst-leaks.mtrace > $@; \
 	$(evaluate-test)
diff --git a/malloc/Makefile b/malloc/Makefile
index 2f9b3d596d..deff659d34 100644
--- a/malloc/Makefile
+++ b/malloc/Makefile
@@ -42,11 +42,11 @@  tests := mallocbug tst-malloc tst-valloc tst-calloc tst-obstack \
 	 tst-malloc-stats-cancellation \
 	 tst-tcfree1 tst-tcfree2 tst-tcfree3 \
 	 tst-safe-linking \
+	 tst-compathooks-off tst-compathooks-on
 
 tests-static := \
 	 tst-interpose-static-nothread \
-	 tst-interpose-static-thread \
-	 tst-malloc-usable-static \
+	 tst-interpose-static-thread
 
 # Test for the malloc_set_state symbol removed in glibc 2.25.
 ifeq ($(have-GLIBC_2.24)$(build-shared),yesyes)
@@ -63,7 +63,6 @@  tests-internal += \
 
 ifneq (no,$(have-tunables))
 tests += tst-malloc-usable-tunables tst-mxfast
-tests-static += tst-malloc-usable-static-tunables
 endif
 
 tests += $(tests-static)
@@ -72,7 +71,8 @@  test-srcs = tst-mtrace
 # These tests either are run with MALLOC_CHECK_=3 by default or do not work
 # with MALLOC_CHECK_=3 because they expect a specific failure.
 tests-exclude-malloc-check = tst-malloc-check tst-malloc-usable \
-	tst-mxfast tst-safe-linking
+	tst-mxfast tst-safe-linking \
+	tst-compathooks-off tst-compathooks-on
 
 # Run all tests with MALLOC_CHECK_=3
 tests-malloc-check = $(filter-out $(tests-exclude-malloc-check),$(tests))
@@ -88,12 +88,11 @@  tests-exclude-mcheck = tst-mallocstate \
 	tst-malloc-tcache-leak \
 	tst-malloc-thread-exit \
 	tst-malloc-thread-fail \
-	tst-malloc-usable-static \
-	tst-malloc-usable-static-tunables \
 	tst-malloc-usable-tunables \
 	tst-malloc_info \
 	tst-memalign \
-	tst-posix_memalign
+	tst-posix_memalign \
+	tst-compathooks-off tst-compathooks-on
 
 tests-mcheck = $(filter-out $(tests-exclude-mcheck), $(tests))
 
@@ -115,8 +114,8 @@  routines = malloc morecore mcheck mtrace obstack reallocarray \
 install-lib := libmcheck.a
 non-lib.a := libmcheck.a
 
-# Additional library.
-extra-libs = libmemusage
+# Additional libraries.
+extra-libs = libmemusage libc_malloc_debug
 extra-libs-others = $(extra-libs)
 
 # Helper objects for some tests.
@@ -131,6 +130,9 @@  test-extras = \
 libmemusage-routines = memusage
 libmemusage-inhibit-o = $(filter-out .os,$(object-suffixes))
 
+libc_malloc_debug-routines = malloc-debug
+libc_malloc_debug-inhibit-o = $(filter-out .os,$(object-suffixes))
+
 $(objpfx)tst-malloc-backtrace: $(shared-thread-library)
 $(objpfx)tst-malloc-thread-exit: $(shared-thread-library)
 $(objpfx)tst-malloc-thread-fail: $(shared-thread-library)
@@ -236,11 +238,12 @@  endif
 endif
 endif
 
-tst-malloc-check-ENV = MALLOC_CHECK_=3
-tst-malloc-usable-ENV = MALLOC_CHECK_=3
-tst-malloc-usable-static-ENV = $(tst-malloc-usable-ENV)
-tst-malloc-usable-tunables-ENV = GLIBC_TUNABLES=glibc.malloc.check=3
-tst-malloc-usable-static-tunables-ENV = $(tst-malloc-usable-tunables-ENV)
+tst-malloc-check-ENV = MALLOC_CHECK_=3 \
+		       LD_PRELOAD=$(objpfx)/libc_malloc_debug.so
+tst-malloc-usable-ENV = MALLOC_CHECK_=3 \
+		       LD_PRELOAD=$(objpfx)/libc_malloc_debug.so
+tst-malloc-usable-tunables-ENV = GLIBC_TUNABLES=glibc.malloc.check=3 \
+				 LD_PRELOAD=$(objpfx)/libc_malloc_debug.so
 
 tst-mxfast-ENV = GLIBC_TUNABLES=glibc.malloc.tcache_count=0:glibc.malloc.mxfast=0
 
@@ -295,12 +298,14 @@  $(objpfx)tst-interpose-static-thread-mcheck: \
 $(objpfx)tst-interpose-static-thread-malloc-check: \
   $(objpfx)tst-interpose-aux-thread.o $(static-thread-library)
 
-tst-dynarray-ENV = MALLOC_TRACE=$(objpfx)tst-dynarray.mtrace
+tst-dynarray-ENV = MALLOC_TRACE=$(objpfx)tst-dynarray.mtrace \
+		   LD_PRELOAD=$(objpfx)libc_malloc_debug.so
 $(objpfx)tst-dynarray-mem.out: $(objpfx)tst-dynarray.out
 	$(common-objpfx)malloc/mtrace $(objpfx)tst-dynarray.mtrace > $@; \
 	$(evaluate-test)
 
-tst-dynarray-fail-ENV = MALLOC_TRACE=$(objpfx)tst-dynarray-fail.mtrace
+tst-dynarray-fail-ENV = MALLOC_TRACE=$(objpfx)tst-dynarray-fail.mtrace \
+			LD_PRELOAD=$(objpfx)libc_malloc_debug.so
 $(objpfx)tst-dynarray-fail-mem.out: $(objpfx)tst-dynarray-fail.out
 	$(common-objpfx)malloc/mtrace $(objpfx)tst-dynarray-fail.mtrace > $@; \
 	$(evaluate-test)
@@ -314,3 +319,10 @@  $(objpfx)tst-mallocfork2-mcheck: $(shared-thread-library)
 $(objpfx)tst-malloc-tcache-leak-malloc-check: $(shared-thread-library)
 $(objpfx)tst-malloc_info-malloc-check: $(shared-thread-library)
 $(objpfx)tst-mallocfork2-malloc-check: $(shared-thread-library)
+
+tst-compathooks-on-ENV = LD_PRELOAD=$(objpfx)libc_malloc_debug.so
+tst-compathooks-on-mcheck-ENV = LD_PRELOAD=$(objpfx)libc_malloc_debug.so
+tst-compathooks-on-malloc-check-ENV = \
+	LD_PRELOAD=$(objpfx)libc_malloc_debug.so
+tst-mallocstate-ENV = LD_PRELOAD=$(objpfx)libc_malloc_debug.so
+tst-mallocstate-malloc-check-ENV = LD_PRELOAD=$(objpfx)libc_malloc_debug.so
diff --git a/malloc/arena.c b/malloc/arena.c
index 7eb110445e..8f890d5ff0 100644
--- a/malloc/arena.c
+++ b/malloc/arena.c
@@ -404,13 +404,6 @@  ptmalloc_init (void)
   if (s && s[0] != '\0' && s[0] != '0')
     __malloc_check_init ();
 #endif
-
-#if HAVE_MALLOC_INIT_HOOK
-  void (*hook) (void) = atomic_forced_read (__malloc_initialize_hook);
-  if (hook != NULL)
-    (*hook)();
-#endif
-  __malloc_initialized = 1;
 }
 
 /* Managing heaps and arenas (for concurrent threads) */
diff --git a/malloc/hooks.c b/malloc/hooks.c
index daa5c7cfae..b18c2b8c90 100644
--- a/malloc/hooks.c
+++ b/malloc/hooks.c
@@ -1,4 +1,4 @@ 
-/* Malloc implementation for multiple threads without lock contention.
+/* Compatibility code for malloc debugging and state management.
    Copyright (C) 2001-2021 Free Software Foundation, Inc.
    This file is part of the GNU C Library.
    Contributed by Wolfram Gloger <wg@malloc.de>, 2001.
@@ -17,32 +17,70 @@ 
    License along with the GNU C Library; see the file COPYING.LIB.  If
    not, see <https://www.gnu.org/licenses/>.  */
 
+#if SHLIB_COMPAT (libc, GLIBC_2_0, GLIBC_2_24)
+void (*__malloc_initialize_hook) (void) __attribute__ ((nocommon));
+compat_symbol (libc, __malloc_initialize_hook,
+	       __malloc_initialize_hook, GLIBC_2_0);
+#endif
+
+static void *malloc_hook_ini (size_t, const void *) __THROW;
+static void *realloc_hook_ini (void *, size_t, const void *) __THROW;
+static void *memalign_hook_ini (size_t, size_t, const void *) __THROW;
+
+void weak_variable (*__free_hook) (void *, const void *) = NULL;
+void *weak_variable (*__malloc_hook)
+  (size_t, const void *) = malloc_hook_ini;
+void *weak_variable (*__realloc_hook)
+  (void *, size_t, const void *) = realloc_hook_ini;
+void *weak_variable (*__memalign_hook)
+  (size_t, size_t, const void *) = memalign_hook_ini;
+
 /* Hooks for debugging versions.  The initial hooks just call the
    initialization routine, then do the normal work. */
 
-static void *
-malloc_hook_ini (size_t sz, const void *caller)
+/* These hooks will get executed only through the interposed allocator
+   functions in libmalloc_compathooks.  This means that the calls to malloc,
+   realloc, etc. will lead back into the interposed functions, which is what we
+   want.
+
+   These initial hooks are assumed to be called in a single-threaded context,
+   so it is safe to reset all hooks at once upon initialization.  */
+
+static void
+generic_hook_ini (void)
 {
   __malloc_hook = NULL;
+  __realloc_hook = NULL;
+  __memalign_hook = NULL;
   ptmalloc_init ();
-  return __libc_malloc (sz);
+
+#if SHLIB_COMPAT (libc, GLIBC_2_0, GLIBC_2_24)
+  void (*hook) (void) = atomic_forced_read (__malloc_initialize_hook);
+  if (hook != NULL)
+    (*hook)();
+#endif
+  __malloc_initialized = 1;
+}
+
+static void *
+malloc_hook_ini (size_t sz, const void *caller)
+{
+  generic_hook_ini ();
+  return malloc (sz);
 }
 
 static void *
 realloc_hook_ini (void *ptr, size_t sz, const void *caller)
 {
-  __malloc_hook = NULL;
-  __realloc_hook = NULL;
-  ptmalloc_init ();
-  return __libc_realloc (ptr, sz);
+  generic_hook_ini ();
+  return realloc (ptr, sz);
 }
 
 static void *
 memalign_hook_ini (size_t alignment, size_t sz, const void *caller)
 {
-  __memalign_hook = NULL;
-  ptmalloc_init ();
-  return __libc_memalign (alignment, sz);
+  generic_hook_ini ();
+  return memalign (alignment, sz);
 }
 
 #include "malloc-check.c"
diff --git a/malloc/malloc-debug.c b/malloc/malloc-debug.c
new file mode 100644
index 0000000000..1c80c33f43
--- /dev/null
+++ b/malloc/malloc-debug.c
@@ -0,0 +1,189 @@ 
+/* Malloc debug DSO.
+   Copyright (C) 2021 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; see the file COPYING.LIB.  If
+   not, see <https://www.gnu.org/licenses/>.  */
+
+#include <atomic.h>
+#include <libc-symbols.h>
+#include <shlib-compat.h>
+#include <string.h>
+#include <unistd.h>
+#include <sys/param.h>
+
+/* Support only the glibc allocators.  */
+extern void *__libc_malloc (size_t);
+extern void __libc_free (void *);
+extern void *__libc_realloc (void *, size_t);
+extern void *__libc_memalign (size_t, size_t);
+extern void *__libc_valloc (size_t);
+extern void *__libc_pvalloc (size_t);
+extern void *__libc_calloc (size_t, size_t);
+
+#define DEBUG_FN(fn) \
+  static __typeof (__libc_ ## fn) __debug_ ## fn
+
+DEBUG_FN(malloc);
+DEBUG_FN(free);
+DEBUG_FN(realloc);
+DEBUG_FN(memalign);
+DEBUG_FN(valloc);
+DEBUG_FN(pvalloc);
+DEBUG_FN(calloc);
+
+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 *);
+compat_symbol_reference (libc, __malloc_hook, __malloc_hook, GLIBC_2_0);
+extern void * (*__realloc_hook) (void *, size_t, const void *);
+compat_symbol_reference (libc, __realloc_hook, __realloc_hook, GLIBC_2_0);
+extern void * (*__memalign_hook) (size_t, size_t, const void *);
+compat_symbol_reference (libc, __memalign_hook, __memalign_hook, GLIBC_2_0);
+
+static size_t pagesize;
+
+/* The allocator functions.  */
+
+static void *
+__debug_malloc (size_t bytes)
+{
+  void *(*hook) (size_t, const void *) = atomic_forced_read (__malloc_hook);
+  if (__builtin_expect (hook != NULL, 0))
+    return (*hook)(bytes, RETURN_ADDRESS (0));
+
+  return __libc_malloc (bytes);
+}
+strong_alias (__debug_malloc, malloc)
+
+static void
+__debug_free (void *mem)
+{
+  void (*hook) (void *, const void *) = atomic_forced_read (__free_hook);
+  if (__builtin_expect (hook != NULL, 0))
+    {
+      (*hook)(mem, RETURN_ADDRESS (0));
+      return;
+    }
+  __libc_free (mem);
+}
+strong_alias (__debug_free, free)
+
+static void *
+__debug_realloc (void *oldmem, size_t bytes)
+{
+  void *(*hook) (void *, size_t, const void *) =
+    atomic_forced_read (__realloc_hook);
+  if (__builtin_expect (hook != NULL, 0))
+    return (*hook)(oldmem, bytes, RETURN_ADDRESS (0));
+
+  return __libc_realloc (oldmem, bytes);
+}
+strong_alias (__debug_realloc, realloc)
+
+static void *
+_mid_memalign (size_t alignment, size_t bytes, const void *address)
+{
+  void *(*hook) (size_t, size_t, const void *) =
+    atomic_forced_read (__memalign_hook);
+  if (__builtin_expect (hook != NULL, 0))
+    return (*hook)(alignment, bytes, address);
+
+  return __libc_memalign (alignment, bytes);
+}
+
+static void *
+__debug_memalign (size_t alignment, size_t bytes)
+{
+  return _mid_memalign (alignment, bytes, RETURN_ADDRESS (0));
+}
+strong_alias (__debug_memalign, memalign)
+strong_alias (__debug_memalign, aligned_alloc)
+
+static void *
+__debug_pvalloc (size_t bytes)
+{
+  size_t rounded_bytes;
+
+  if (!pagesize)
+    pagesize = sysconf (_SC_PAGESIZE);
+
+  /* ALIGN_UP with overflow check.  */
+  if (__glibc_unlikely (__builtin_add_overflow (bytes,
+						pagesize - 1,
+						&rounded_bytes)))
+    {
+      errno = ENOMEM;
+      return NULL;
+    }
+  rounded_bytes = rounded_bytes & -(pagesize - 1);
+
+  return _mid_memalign (pagesize, rounded_bytes, RETURN_ADDRESS (0));
+}
+strong_alias (__debug_pvalloc, pvalloc)
+
+static void *
+__debug_valloc (size_t bytes)
+{
+  if (!pagesize)
+    pagesize = sysconf (_SC_PAGESIZE);
+
+  return _mid_memalign (pagesize, bytes, RETURN_ADDRESS (0));
+}
+strong_alias (__debug_valloc, valloc)
+
+static int
+__debug_posix_memalign (void **memptr, size_t alignment, size_t bytes)
+{
+  /* Test whether the SIZE argument is valid.  It must be a power of
+     two multiple of sizeof (void *).  */
+  if (alignment % sizeof (void *) != 0
+      || !powerof2 (alignment / sizeof (void *))
+      || alignment == 0)
+    return EINVAL;
+
+  *memptr = _mid_memalign (alignment, bytes, RETURN_ADDRESS (0));
+
+  if (*memptr == NULL)
+    return ENOMEM;
+
+  return 0;
+}
+strong_alias (__debug_posix_memalign, posix_memalign)
+
+static void *
+__debug_calloc (size_t nmemb, size_t size)
+{
+  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)
+	memset (mem, 0, bytes);
+
+      return mem;
+    }
+
+  return __libc_calloc (nmemb, size);
+}
+strong_alias (__debug_calloc, calloc)
diff --git a/malloc/malloc.c b/malloc/malloc.c
index bb9a1642aa..d2e45664b1 100644
--- a/malloc/malloc.c
+++ b/malloc/malloc.c
@@ -570,16 +570,6 @@  tag_at (void *ptr)
 #define HAVE_MREMAP 0
 #endif
 
-/* We may need to support __malloc_initialize_hook for backwards
-   compatibility.  */
-
-#if SHLIB_COMPAT (libc, GLIBC_2_0, GLIBC_2_24)
-# define HAVE_MALLOC_INIT_HOOK 1
-#else
-# define HAVE_MALLOC_INIT_HOOK 0
-#endif
-
-
 /*
   This version of malloc supports the standard SVID/XPG mallinfo
   routine that returns a struct containing usage properties and
@@ -2013,30 +2003,6 @@  static void     malloc_consolidate (mstate);
 # define weak_variable weak_function
 #endif
 
-/* Forward declarations.  */
-static void *malloc_hook_ini (size_t sz,
-                              const void *caller) __THROW;
-static void *realloc_hook_ini (void *ptr, size_t sz,
-                               const void *caller) __THROW;
-static void *memalign_hook_ini (size_t alignment, size_t sz,
-                                const void *caller) __THROW;
-
-#if HAVE_MALLOC_INIT_HOOK
-void (*__malloc_initialize_hook) (void) __attribute__ ((nocommon));
-compat_symbol (libc, __malloc_initialize_hook,
-	       __malloc_initialize_hook, GLIBC_2_0);
-#endif
-
-void weak_variable (*__free_hook) (void *__ptr,
-                                   const void *) = NULL;
-void *weak_variable (*__malloc_hook)
-  (size_t __size, const void *) = malloc_hook_ini;
-void *weak_variable (*__realloc_hook)
-  (void *__ptr, size_t __size, const void *)
-  = realloc_hook_ini;
-void *weak_variable (*__memalign_hook)
-  (size_t __alignment, size_t __size, const void *)
-  = memalign_hook_ini;
 void weak_variable (*__after_morecore_hook) (void) = NULL;
 
 /* This function is called from the arena shutdown hook, to free the
@@ -3229,10 +3195,8 @@  __libc_malloc (size_t bytes)
   _Static_assert (PTRDIFF_MAX <= SIZE_MAX / 2,
                   "PTRDIFF_MAX is not more than half of SIZE_MAX");
 
-  void *(*hook) (size_t, const void *)
-    = atomic_forced_read (__malloc_hook);
-  if (__builtin_expect (hook != NULL, 0))
-    return (*hook)(bytes, RETURN_ADDRESS (0));
+  if (__malloc_initialized < 0)
+    ptmalloc_init ();
 #if USE_TCACHE
   /* int_free also calls request2size, be careful to not pad twice.  */
   size_t tbytes;
@@ -3293,14 +3257,6 @@  __libc_free (void *mem)
   mstate ar_ptr;
   mchunkptr p;                          /* chunk corresponding to mem */
 
-  void (*hook) (void *, const void *)
-    = atomic_forced_read (__free_hook);
-  if (__builtin_expect (hook != NULL, 0))
-    {
-      (*hook)(mem, RETURN_ADDRESS (0));
-      return;
-    }
-
   if (mem == 0)                              /* free(0) has no effect */
     return;
 
@@ -3352,10 +3308,8 @@  __libc_realloc (void *oldmem, size_t bytes)
 
   void *newp;             /* chunk to return */
 
-  void *(*hook) (void *, size_t, const void *) =
-    atomic_forced_read (__realloc_hook);
-  if (__builtin_expect (hook != NULL, 0))
-    return (*hook)(oldmem, bytes, RETURN_ADDRESS (0));
+  if (__malloc_initialized < 0)
+    ptmalloc_init ();
 
 #if REALLOC_ZERO_BYTES_FREES
   if (bytes == 0 && oldmem != NULL)
@@ -3490,6 +3444,9 @@  libc_hidden_def (__libc_realloc)
 void *
 __libc_memalign (size_t alignment, size_t bytes)
 {
+  if (__malloc_initialized < 0)
+    ptmalloc_init ();
+
   void *address = RETURN_ADDRESS (0);
   return _mid_memalign (alignment, bytes, address);
 }
@@ -3500,11 +3457,6 @@  _mid_memalign (size_t alignment, size_t bytes, void *address)
   mstate ar_ptr;
   void *p;
 
-  void *(*hook) (size_t, size_t, const void *) =
-    atomic_forced_read (__memalign_hook);
-  if (__builtin_expect (hook != NULL, 0))
-    return (*hook)(alignment, bytes, address);
-
   /* If we need less alignment than we give anyway, just relay to malloc.  */
   if (alignment <= MALLOC_ALIGNMENT)
     return __libc_malloc (bytes);
@@ -3613,16 +3565,8 @@  __libc_calloc (size_t n, size_t elem_size)
 
   sz = bytes;
 
-  void *(*hook) (size_t, const void *) =
-    atomic_forced_read (__malloc_hook);
-  if (__builtin_expect (hook != NULL, 0))
-    {
-      mem = (*hook)(sz, RETURN_ADDRESS (0));
-      if (mem == 0)
-        return 0;
-
-      return memset (mem, 0, sz);
-    }
+  if (__malloc_initialized < 0)
+    ptmalloc_init ();
 
   MAYBE_INIT_TCACHE ();
 
@@ -5651,6 +5595,9 @@  __posix_memalign (void **memptr, size_t alignment, size_t size)
 {
   void *mem;
 
+  if (__malloc_initialized < 0)
+    ptmalloc_init ();
+
   /* Test whether the SIZE argument is valid.  It must be a power of
      two multiple of sizeof (void *).  */
   if (alignment % sizeof (void *) != 0
diff --git a/malloc/mcheck.c b/malloc/mcheck.c
index 2a1fc645d4..b46b9b26bf 100644
--- a/malloc/mcheck.c
+++ b/malloc/mcheck.c
@@ -25,6 +25,7 @@ 
 # include <stdio.h>
 # include <libintl.h>
 # include <errno.h>
+# include <malloc-internal.h>
 #endif
 
 /* Old hook values.  */
diff --git a/malloc/mtrace.c b/malloc/mtrace.c
index f5b8321c6b..274db3fb47 100644
--- a/malloc/mtrace.c
+++ b/malloc/mtrace.c
@@ -22,6 +22,7 @@ 
 # define _MALLOC_INTERNAL
 # include <malloc.h>
 # include <mcheck.h>
+# include <malloc-internal.h>
 # include <libc-lock.h>
 #endif
 
diff --git a/malloc/tst-compathooks-off.c b/malloc/tst-compathooks-off.c
new file mode 100644
index 0000000000..b1290cf367
--- /dev/null
+++ b/malloc/tst-compathooks-off.c
@@ -0,0 +1,145 @@ 
+/* Minimal tests to verify libmalloc_compathooks.so functionality.
+   Copyright (C) 2021 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/>.  */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <malloc.h>
+#include <shlib-compat.h>
+#include <libc-diag.h>
+
+#include <support/check.h>
+#include <support/support.h>
+
+extern void (*volatile __free_hook) (void *, const void *);
+extern void *(*volatile __malloc_hook)(size_t, const void *);
+extern void *(*volatile __realloc_hook)(void *, size_t, const void *);
+extern void *(*volatile __memalign_hook)(size_t, size_t, const void *);
+
+int hook_count, call_count;
+
+DIAG_PUSH_NEEDS_COMMENT;
+DIAG_IGNORE_NEEDS_COMMENT (4.9, "-Wdeprecated-declarations");
+
+void
+free_called (void *mem, const void *address)
+{
+  hook_count++;
+  __free_hook = NULL;
+  free (mem);
+  __free_hook = free_called;
+}
+
+void *
+malloc_called (size_t bytes, const void *address)
+{
+  hook_count++;
+  __malloc_hook = NULL;
+  void *mem = malloc (bytes);
+  __malloc_hook = malloc_called;
+  return mem;
+}
+
+void *
+realloc_called (void *oldptr, size_t bytes, const void *address)
+{
+  hook_count++;
+  __realloc_hook = NULL;
+  void *mem = realloc (oldptr, bytes);
+  __realloc_hook = realloc_called;
+  return mem;
+}
+
+void *
+calloc_called (size_t n, size_t size, const void *address)
+{
+  hook_count++;
+  __malloc_hook = NULL;
+  void *mem = calloc (n, size);
+  __malloc_hook = malloc_called;
+  return mem;
+}
+
+void *
+memalign_called (size_t align, size_t size, const void *address)
+{
+  hook_count++;
+  __memalign_hook = NULL;
+  void *mem = memalign (align, size);
+  __memalign_hook = memalign_called;
+  return mem;
+}
+
+static void initialize_hooks (void)
+{
+  __free_hook = free_called;
+  __malloc_hook = malloc_called;
+  __realloc_hook = realloc_called;
+  __memalign_hook = memalign_called;
+}
+void (*__malloc_initialize_hook) (void) = initialize_hooks;
+compat_symbol_reference (libc, __malloc_initialize_hook,
+			 __malloc_initialize_hook, GLIBC_2_0);
+compat_symbol_reference (libc, __free_hook,
+			 __free_hook, GLIBC_2_0);
+compat_symbol_reference (libc, __malloc_hook,
+			 __malloc_hook, GLIBC_2_0);
+compat_symbol_reference (libc, __realloc_hook,
+			 __realloc_hook, GLIBC_2_0);
+compat_symbol_reference (libc, __memalign_hook,
+			 __memalign_hook, GLIBC_2_0);
+
+DIAG_POP_NEEDS_COMMENT;
+
+static int
+do_test (void)
+{
+  void *p;
+  p = malloc (0);
+  TEST_VERIFY_EXIT (p != NULL);
+  call_count++;
+
+  p = realloc (p, 0);
+  TEST_VERIFY_EXIT (p == NULL);
+  call_count++;
+
+  p = calloc (512, 1);
+  TEST_VERIFY_EXIT (p != NULL);
+  call_count++;
+
+  free (p);
+  call_count++;
+
+  p = memalign (0x100, 0x100);
+  TEST_VERIFY_EXIT (p != NULL);
+  call_count++;
+
+  free (p);
+  call_count++;
+
+  printf ("call_count: %d, hook_count: %d\n", call_count, hook_count);
+
+#ifdef HOOKS_ENABLED
+  TEST_VERIFY_EXIT (call_count == hook_count);
+#else
+  TEST_VERIFY_EXIT (hook_count == 0);
+#endif
+
+  exit (0);
+}
+
+#include <support/test-driver.c>
diff --git a/malloc/tst-compathooks-on.c b/malloc/tst-compathooks-on.c
new file mode 100644
index 0000000000..4da183687a
--- /dev/null
+++ b/malloc/tst-compathooks-on.c
@@ -0,0 +1,2 @@ 
+#define HOOKS_ENABLED 1
+#include "tst-compathooks-off.c"
diff --git a/malloc/tst-malloc-usable-static-tunables.c b/malloc/tst-malloc-usable-static-tunables.c
deleted file mode 100644
index 8907db01a5..0000000000
--- a/malloc/tst-malloc-usable-static-tunables.c
+++ /dev/null
@@ -1 +0,0 @@ 
-#include <malloc/tst-malloc-usable.c>
diff --git a/malloc/tst-malloc-usable-static.c b/malloc/tst-malloc-usable-static.c
deleted file mode 100644
index 8907db01a5..0000000000
--- a/malloc/tst-malloc-usable-static.c
+++ /dev/null
@@ -1 +0,0 @@ 
-#include <malloc/tst-malloc-usable.c>
diff --git a/malloc/tst-mtrace.sh b/malloc/tst-mtrace.sh
index 9295683aff..a830204d5e 100755
--- a/malloc/tst-mtrace.sh
+++ b/malloc/tst-mtrace.sh
@@ -30,6 +30,7 @@  trap "rm -f ${common_objpfx}malloc/tst-mtrace.leak; exit 1" 1 2 15
 ${test_program_prefix_before_env} \
 ${run_program_env} \
 MALLOC_TRACE=${common_objpfx}malloc/tst-mtrace.leak \
+LD_PRELOAD=${common_objpfx}malloc/libc_malloc_debug.so \
 ${test_program_prefix_after_env} \
   ${common_objpfx}malloc/tst-mtrace || status=1
 
diff --git a/manual/memory.texi b/manual/memory.texi
index 28ec2e4e63..0aae1f8720 100644
--- a/manual/memory.texi
+++ b/manual/memory.texi
@@ -1256,8 +1256,9 @@  environment variable @env{MALLOC_ARENA_MAX} to the desired value.
 @cindex consistency checking, of heap
 
 You can ask @code{malloc} to check the consistency of dynamic memory by
-using the @code{mcheck} function.  This function is a GNU extension,
-declared in @file{mcheck.h}.
+using the @code{mcheck} function and preloading the malloc debug library
+@file{libc_malloc_debug.so} using the @var{LD_PRELOAD} environment variable.
+This function is a GNU extension, declared in @file{mcheck.h}.
 @pindex mcheck.h
 
 @deftypefun int mcheck (void (*@var{abortfn}) (enum mcheck_status @var{status}))
@@ -1368,7 +1369,10 @@  non-zero value, a special (less efficient) implementation is used which
 is designed to be tolerant against simple errors, such as double calls
 of @code{free} with the same argument, or overruns of a single byte
 (off-by-one bugs).  Not all such errors can be protected against,
-however, and memory leaks can result.
+however, and memory leaks can result.  Like in the case of @code{mcheck},
+one would need to preload the @file{libc_malloc_debug.so} library to
+enable @code{MALLOC_CHECK_} functionality.  Without this preloaded
+library, setting @code{MALLOC_CHECK_} will have no effect.
 
 Any detected heap corruption results in immediate termination of the
 process.
@@ -1747,6 +1751,12 @@  penalties for the program if the debugging mode is not enabled.
 @c  fprintf dup (on newly-created stream) @aculock
 @c  __cxa_atexit (once) dup @asulock @aculock @acsmem
 @c  free dup @ascuheap @acsmem
+The @code{mtrace} function provides a way to trace memory allocation
+events in the program that calls it.  It is disabled by default in the
+library and can be enabled by preloading the debugging library
+@file{libc_malloc_debug.so} using the @code{LD_PRELOAD} environment
+variable.
+
 When the @code{mtrace} function is called it looks for an environment
 variable named @code{MALLOC_TRACE}.  This variable is supposed to
 contain a valid file name.  The user must have write access.  If the
diff --git a/manual/tunables.texi b/manual/tunables.texi
index d5d957fb5b..b9c52a0090 100644
--- a/manual/tunables.texi
+++ b/manual/tunables.texi
@@ -113,7 +113,9 @@  following tunables in the @code{malloc} namespace:
 
 @deftp Tunable glibc.malloc.check
 This tunable supersedes the @env{MALLOC_CHECK_} environment variable and is
-identical in features.
+identical in features. This tunable has no effect by default and needs the
+debug library @file{libc_malloc_debug.so} to be preloaded using the
+@code{LD_PRELOAD} environment variable.
 
 Setting this tunable to a non-zero value enables a special (less
 efficient) memory allocator for the @code{malloc} family of functions that is
diff --git a/misc/Makefile b/misc/Makefile
index ae03e26f1b..b144a3df6c 100644
--- a/misc/Makefile
+++ b/misc/Makefile
@@ -152,13 +152,15 @@  $(objpfx)libg.a: $(dep-dummy-lib); $(make-dummy-lib)
 
 $(objpfx)tst-tsearch: $(libm)
 
-tst-error1-ENV = MALLOC_TRACE=$(objpfx)tst-error1.mtrace
+tst-error1-ENV = MALLOC_TRACE=$(objpfx)tst-error1.mtrace \
+		 LD_PRELOAD=$(common-objpfx)/malloc/libc_malloc_debug.so
 tst-error1-ARGS = $(objpfx)tst-error1.out
 $(objpfx)tst-error1-mem.out: $(objpfx)tst-error1.out
 	$(common-objpfx)malloc/mtrace $(objpfx)tst-error1.mtrace > $@; \
 	$(evaluate-test)
 
-tst-allocate_once-ENV = MALLOC_TRACE=$(objpfx)tst-allocate_once.mtrace
+tst-allocate_once-ENV = MALLOC_TRACE=$(objpfx)tst-allocate_once.mtrace \
+			LD_PRELOAD=$(common-objpfx)/malloc/libc_malloc_debug.so
 $(objpfx)tst-allocate_once-mem.out: $(objpfx)tst-allocate_once.out
 	$(common-objpfx)malloc/mtrace $(objpfx)tst-allocate_once.mtrace > $@; \
 	$(evaluate-test)
diff --git a/nptl/Makefile b/nptl/Makefile
index 9b94bfcd31..ff4d590f11 100644
--- a/nptl/Makefile
+++ b/nptl/Makefile
@@ -494,7 +494,8 @@  CFLAGS-tst-initializers1-gnu11.c += $(CFLAGS-tst-initializers1-<)
 tst-cancel7-ARGS = --command "exec $(host-test-program-cmd)"
 tst-cancelx7-ARGS = $(tst-cancel7-ARGS)
 
-tst-stack3-ENV = MALLOC_TRACE=$(objpfx)tst-stack3.mtrace
+tst-stack3-ENV = MALLOC_TRACE=$(objpfx)tst-stack3.mtrace \
+		 LD_PRELOAD=$(common-objpfx)/malloc/libc_malloc_debug.so
 $(objpfx)tst-stack3-mem.out: $(objpfx)tst-stack3.out
 	$(common-objpfx)malloc/mtrace $(objpfx)tst-stack3.mtrace > $@; \
 	$(evaluate-test)
diff --git a/posix/Makefile b/posix/Makefile
index e91ea25ba1..3f1649369a 100644
--- a/posix/Makefile
+++ b/posix/Makefile
@@ -311,43 +311,50 @@  annexc-CFLAGS = -O
 $(objpfx)annexc: annexc.c
 	$(native-compile)
 
-tst-fnmatch-ENV += MALLOC_TRACE=$(objpfx)tst-fnmatch.mtrace
+tst-fnmatch-ENV += MALLOC_TRACE=$(objpfx)tst-fnmatch.mtrace \
+		   LD_PRELOAD=$(common-objpfx)/malloc/libc_malloc_debug.so
 
 $(objpfx)tst-fnmatch-mem.out: $(objpfx)tst-fnmatch.out
 	$(common-objpfx)malloc/mtrace $(objpfx)tst-fnmatch.mtrace > $@; \
 	$(evaluate-test)
 
-bug-regex2-ENV = MALLOC_TRACE=$(objpfx)bug-regex2.mtrace
+bug-regex2-ENV = MALLOC_TRACE=$(objpfx)bug-regex2.mtrace \
+		 LD_PRELOAD=$(common-objpfx)/malloc/libc_malloc_debug.so
 
 $(objpfx)bug-regex2-mem.out: $(objpfx)bug-regex2.out
 	$(common-objpfx)malloc/mtrace $(objpfx)bug-regex2.mtrace > $@; \
 	$(evaluate-test)
 
-bug-regex14-ENV = MALLOC_TRACE=$(objpfx)bug-regex14.mtrace
+bug-regex14-ENV = MALLOC_TRACE=$(objpfx)bug-regex14.mtrace \
+		  LD_PRELOAD=$(common-objpfx)/malloc/libc_malloc_debug.so
 
 $(objpfx)bug-regex14-mem.out: $(objpfx)bug-regex14.out
 	$(common-objpfx)malloc/mtrace $(objpfx)bug-regex14.mtrace > $@; \
 	$(evaluate-test)
 
-bug-regex21-ENV = MALLOC_TRACE=$(objpfx)bug-regex21.mtrace
+bug-regex21-ENV = MALLOC_TRACE=$(objpfx)bug-regex21.mtrace \
+		  LD_PRELOAD=$(common-objpfx)/malloc/libc_malloc_debug.so
 
 $(objpfx)bug-regex21-mem.out: $(objpfx)bug-regex21.out
 	$(common-objpfx)malloc/mtrace $(objpfx)bug-regex21.mtrace > $@; \
 	$(evaluate-test)
 
-bug-regex31-ENV = MALLOC_TRACE=$(objpfx)bug-regex31.mtrace
+bug-regex31-ENV = MALLOC_TRACE=$(objpfx)bug-regex31.mtrace \
+		  LD_PRELOAD=$(common-objpfx)/malloc/libc_malloc_debug.so
 
 $(objpfx)bug-regex31-mem.out: $(objpfx)bug-regex31.out
 	$(common-objpfx)malloc/mtrace $(objpfx)bug-regex31.mtrace > $@; \
 	$(evaluate-test)
 
-bug-regex36-ENV = MALLOC_TRACE=$(objpfx)bug-regex36.mtrace
+bug-regex36-ENV = MALLOC_TRACE=$(objpfx)bug-regex36.mtrace \
+		  LD_PRELOAD=$(common-objpfx)/malloc/libc_malloc_debug.so
 
 $(objpfx)bug-regex36-mem.out: $(objpfx)bug-regex36.out
 	$(common-objpfx)malloc/mtrace $(objpfx)bug-regex36.mtrace > $@; \
 	$(evaluate-test)
 
-tst-vfork3-ENV = MALLOC_TRACE=$(objpfx)tst-vfork3.mtrace
+tst-vfork3-ENV = MALLOC_TRACE=$(objpfx)tst-vfork3.mtrace \
+		 LD_PRELOAD=$(common-objpfx)/malloc/libc_malloc_debug.so
 
 $(objpfx)tst-vfork3-mem.out: $(objpfx)tst-vfork3.out
 	$(common-objpfx)malloc/mtrace $(objpfx)tst-vfork3.mtrace > $@; \
@@ -356,18 +363,22 @@  $(objpfx)tst-vfork3-mem.out: $(objpfx)tst-vfork3.out
 # tst-rxspencer.mtrace is not generated, only
 # tst-rxspencer-no-utf8.mtrace, since otherwise the file has almost
 # 100M and takes very long time to process.
-tst-rxspencer-no-utf8-ENV += MALLOC_TRACE=$(objpfx)tst-rxspencer-no-utf8.mtrace
+tst-rxspencer-no-utf8-ENV += \
+  MALLOC_TRACE=$(objpfx)tst-rxspencer-no-utf8.mtrace \
+  LD_PRELOAD=$(common-objpfx)/malloc/libc_malloc_debug.so
 $(objpfx)tst-rxspencer-no-utf8-mem.out: $(objpfx)tst-rxspencer-no-utf8.out
 	$(common-objpfx)malloc/mtrace $(objpfx)tst-rxspencer-no-utf8.mtrace \
 				      > $@; \
 	$(evaluate-test)
 
-tst-pcre-ENV = MALLOC_TRACE=$(objpfx)tst-pcre.mtrace
+tst-pcre-ENV = MALLOC_TRACE=$(objpfx)tst-pcre.mtrace \
+	       LD_PRELOAD=$(common-objpfx)/malloc/libc_malloc_debug.so
 $(objpfx)tst-pcre-mem.out: $(objpfx)tst-pcre.out
 	$(common-objpfx)malloc/mtrace $(objpfx)tst-pcre.mtrace > $@; \
 	$(evaluate-test)
 
-tst-boost-ENV = MALLOC_TRACE=$(objpfx)tst-boost.mtrace
+tst-boost-ENV = MALLOC_TRACE=$(objpfx)tst-boost.mtrace \
+		LD_PRELOAD=$(common-objpfx)/malloc/libc_malloc_debug.so
 $(objpfx)tst-boost-mem.out: $(objpfx)tst-boost.out
 	$(common-objpfx)malloc/mtrace $(objpfx)tst-boost.mtrace > $@; \
 	$(evaluate-test)
@@ -382,15 +393,18 @@  $(objpfx)bug-ga2-mem.out: $(objpfx)bug-ga2.out
 	&& $(common-objpfx)malloc/mtrace $(objpfx)bug-ga2.mtrace; } > $@; \
 	$(evaluate-test)
 
-bug-ga2-ENV = MALLOC_TRACE=$(objpfx)bug-ga2.mtrace
+bug-ga2-ENV = MALLOC_TRACE=$(objpfx)bug-ga2.mtrace \
+	      LD_PRELOAD=$(common-objpfx)/malloc/libc_malloc_debug.so
 
-bug-glob2-ENV = MALLOC_TRACE=$(objpfx)bug-glob2.mtrace
+bug-glob2-ENV = MALLOC_TRACE=$(objpfx)bug-glob2.mtrace \
+		LD_PRELOAD=$(common-objpfx)/malloc/libc_malloc_debug.so
 
 $(objpfx)bug-glob2-mem.out: $(objpfx)bug-glob2.out
 	$(common-objpfx)malloc/mtrace $(objpfx)bug-glob2.mtrace > $@; \
 	$(evaluate-test)
 
-tst-glob-tilde-ENV = MALLOC_TRACE=$(objpfx)tst-glob-tilde.mtrace
+tst-glob-tilde-ENV = MALLOC_TRACE=$(objpfx)tst-glob-tilde.mtrace \
+		     LD_PRELOAD=$(common-objpfx)/malloc/libc_malloc_debug.so
 
 $(objpfx)tst-glob-tilde-mem.out: $(objpfx)tst-glob-tilde.out
 	$(common-objpfx)malloc/mtrace $(objpfx)tst-glob-tilde.mtrace > $@; \
diff --git a/resolv/Makefile b/resolv/Makefile
index 1d3565d478..09b2f129eb 100644
--- a/resolv/Makefile
+++ b/resolv/Makefile
@@ -156,19 +156,22 @@  $(objpfx)tst-res_hconf_reorder: $(shared-thread-library)
 tst-res_hconf_reorder-ENV = RESOLV_REORDER=on
 
 $(objpfx)tst-leaks: $(objpfx)libresolv.so
-tst-leaks-ENV = MALLOC_TRACE=$(objpfx)tst-leaks.mtrace
+tst-leaks-ENV = MALLOC_TRACE=$(objpfx)tst-leaks.mtrace \
+		LD_PRELOAD=$(common-objpfx)/malloc/libc_malloc_debug.so
 $(objpfx)mtrace-tst-leaks.out: $(objpfx)tst-leaks.out
 	$(common-objpfx)malloc/mtrace $(objpfx)tst-leaks.mtrace > $@; \
 	$(evaluate-test)
 
-tst-leaks2-ENV = MALLOC_TRACE=$(objpfx)tst-leaks2.mtrace
+tst-leaks2-ENV = MALLOC_TRACE=$(objpfx)tst-leaks2.mtrace \
+		 LD_PRELOAD=$(common-objpfx)/malloc/libc_malloc_debug.so
 $(objpfx)mtrace-tst-leaks2.out: $(objpfx)tst-leaks2.out
 	{ test -r $(objpfx)tst-leaks2.mtrace \
 	|| ( echo "tst-leaks2.mtrace does not exist"; exit 77; ) \
 	&& $(common-objpfx)malloc/mtrace $(objpfx)tst-leaks2.mtrace; } > $@; \
 	$(evaluate-test)
 
-tst-resolv-res_ninit-ENV = MALLOC_TRACE=$(objpfx)tst-resolv-res_ninit.mtrace
+tst-resolv-res_ninit-ENV = MALLOC_TRACE=$(objpfx)tst-resolv-res_ninit.mtrace \
+			LD_PRELOAD=$(common-objpfx)/malloc/libc_malloc_debug.so
 $(objpfx)mtrace-tst-resolv-res_ninit.out: $(objpfx)tst-resolv-res_ninit.out
 	$(common-objpfx)malloc/mtrace \
 	  $(objpfx)tst-resolv-res_ninit.mtrace > $@; \
diff --git a/stdio-common/Makefile b/stdio-common/Makefile
index f87796a8ce..803f16dae0 100644
--- a/stdio-common/Makefile
+++ b/stdio-common/Makefile
@@ -110,15 +110,20 @@  $(objpfx)tst-swprintf.out: $(gen-locales)
 $(objpfx)tst-vfprintf-mbs-prec.out: $(gen-locales)
 endif
 
-tst-printf-bz18872-ENV = MALLOC_TRACE=$(objpfx)tst-printf-bz18872.mtrace
+tst-printf-bz18872-ENV = MALLOC_TRACE=$(objpfx)tst-printf-bz18872.mtrace \
+			LD_PRELOAD=$(common-objpfx)/malloc/libc_malloc_debug.so
 tst-vfprintf-width-prec-ENV = \
-  MALLOC_TRACE=$(objpfx)tst-vfprintf-width-prec.mtrace
+  MALLOC_TRACE=$(objpfx)tst-vfprintf-width-prec.mtrace \
+  LD_PRELOAD=$(common-objpfx)/malloc/libc_malloc_debug.so
 tst-printf-bz25691-ENV = \
-  MALLOC_TRACE=$(objpfx)tst-printf-bz25691.mtrace
+  MALLOC_TRACE=$(objpfx)tst-printf-bz25691.mtrace \
+  LD_PRELOAD=$(common-objpfx)/malloc/libc_malloc_debug.so
 tst-printf-fp-free-ENV = \
-  MALLOC_TRACE=$(objpfx)tst-printf-fp-free.mtrace
+  MALLOC_TRACE=$(objpfx)tst-printf-fp-free.mtrace \
+  LD_PRELOAD=$(common-objpfx)/malloc/libc_malloc_debug.so
 tst-printf-fp-leak-ENV = \
-  MALLOC_TRACE=$(objpfx)tst-printf-fp-leak.mtrace
+  MALLOC_TRACE=$(objpfx)tst-printf-fp-leak.mtrace \
+  LD_PRELOAD=$(common-objpfx)/malloc/libc_malloc_debug.so
 
 $(objpfx)tst-unbputc.out: tst-unbputc.sh $(objpfx)tst-unbputc
 	$(SHELL) $< $(common-objpfx) '$(test-program-prefix)'; \
diff --git a/sysdeps/pthread/Makefile b/sysdeps/pthread/Makefile
index 9b862b93c4..42f9fc5072 100644
--- a/sysdeps/pthread/Makefile
+++ b/sysdeps/pthread/Makefile
@@ -211,7 +211,8 @@  tst-umask1-ARGS = $(objpfx)tst-umask1.temp
 
 $(objpfx)tst-atfork2: $(shared-thread-library)
 LDFLAGS-tst-atfork2 = -rdynamic
-tst-atfork2-ENV = MALLOC_TRACE=$(objpfx)tst-atfork2.mtrace
+tst-atfork2-ENV = MALLOC_TRACE=$(objpfx)tst-atfork2.mtrace \
+		  LD_PRELOAD=$(common-objpfx)/malloc/libc_malloc_debug.so
 $(objpfx)tst-atfork2mod.so: $(shared-thread-library)
 
 ifeq ($(build-shared),yes)