threads / patch / 46344

patch, 5 partsbuilding git with clang/gcc address sanitizer

Subject: [PATCH 0/5] building git with clang/gcc address sanitizer

## tl;dr

18 messages between Jul 10, 2017 and Jul 16, 2017. Diffs are folded; open one to read it.

replies: 17people: 5as markdown or json

Jeff King· Jul 10, 2017, 13:24 UTC · lore

I mentioned recently that I sometimes run the test suite with ASan, so here are a few tweaks to make this easier (most of which I've been carrying in my personal config.mak for a few years).

In my experience ASan does at least as well as valgrind at finding memory bugs, and runs way faster. With this series, running:

  make SANITIZE=address test

takes about 4.5 minutes on my machine. A normal build+test is about 1.5 minutes on the same machine. I haven't timed a full run with --valgrind recently, but I know that it is much much slower. :)

If you want to see it in action, you can do:
  make SANITIZE=address
  ./git log -g HEAD HEAD >/dev/null
which finds a bug I recently fixed (but the fix isn't in master yet).
There are other sanitizers, too. I _thought_ I had
  make SANITIZE=undefined test

running cleanly at one point, but it's definitely not clean now. Patch 5 helps a little by disabling unaligned loads in our get_be32() macros. Once upon a time I had to set INTERNAL_QSORT, but it isn't necessary anymore since everything goes through sane_qsort(). Most of the remaining bugs are of a similar form, doing something like:

  memcpy(NULL, NULL, 0);

I don't know if it's worth having a sane_memcpy() there, or simply tweaking the code to avoid the call (almost all of them are a single call from apply.c:2870).

It looks like we also have a case of shifting off the left side of a signed int, which is undefined.

You can also try:
  make SANITIZE=thread test

but it's not clean. I poked at some of the errors, and I don't think there a problem in practice (though they may be worth cleaning up in the name of code hygiene).

There's also:
  make SANITIZE=memory test

This is clang-only. It's supposed to find uses of uninitialized memory. But it complains about writing out anything that zlib has touched. I seem to recall that valgrind had a similar problem. I'm not sure what zlib does to confuse these analyzers. For valgrind we were able to add a suppression. We could probably do the same here, but I haven't looked into it.

  [1/5]: test-lib: set ASAN_OPTIONS variable before we run git
  [2/5]: test-lib: turn on ASan abort_on_error by default
  [3/5]: Makefile: add helper for compiling with -fsanitize
  [4/5]: Makefile: turn off -fomit-frame-pointer with sanitizers
  [5/5]: Makefile: disable unaligned loads with UBSan
 Makefile      |  8 ++++++++
 t/test-lib.sh | 11 ++++++++---
 2 files changed, 16 insertions(+), 3 deletions(-)
-Peff
Jeff King· Jul 10, 2017, 13:24 UTC · re: Jeff King · lore

[PATCH 1/5] test-lib: set ASAN_OPTIONS variable before we run git

We turn off ASan's leak detection by default in the test suite because it's too noisy. But we don't do so until part-way through test-lib. This is before we've run any tests, but after we do our initial "./git" to see if the binary has even been built.

When built with clang, this seems to work fine. However, using "gcc -fsanitize=address", the leak checker seems to complain more aggressively:

  $ ./git
  ...
  ==5352==ERROR: LeakSanitizer: detected memory leaks
  Direct leak of 2 byte(s) in 1 object(s) allocated from:
      #0 0x7f120e7afcf8 in malloc (/usr/lib/x86_64-linux-gnu/libasan.so.3+0xc1cf8)
      #1 0x559fc2a3ce41 in do_xmalloc /home/peff/compile/git/wrapper.c:60
      #2 0x559fc2a3cf1a in do_xmallocz /home/peff/compile/git/wrapper.c:100
      #3 0x559fc2a3d0ad in xmallocz /home/peff/compile/git/wrapper.c:108
      #4 0x559fc2a3d0ad in xmemdupz /home/peff/compile/git/wrapper.c:124
      #5 0x559fc2a3d0ad in xstrndup /home/peff/compile/git/wrapper.c:130
      #6 0x559fc274535a in main /home/peff/compile/git/common-main.c:39
      #7 0x7f120dabd2b0 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x202b0)

This is a leak in the sense that we never free it, but it's in a global that is meant to last the whole program. So it's not really interesting or in need of fixing. And at any rate, mentioning leaks outside of the test_expect blocks is certainly unwelcome, as it pollutes stderr.

Let's bump the setting of ASAN_OPTIONS higher in test-lib.sh to catch our initial "can we even run git?" test. While we're at it, we can add a comment to make it a bit less inscrutable.

Signed-off-by: Jeff King <peff@peff.net>
---
 t/test-lib.sh | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)
Show changes to t/test-lib.sh +8 −3
diff --git a/t/test-lib.sh b/t/test-lib.sh
index 2306574dc..961194a50 100644
--- a/t/test-lib.sh
+++ b/t/test-lib.sh
@@ -36,6 +36,14 @@ then
 fi
 GIT_BUILD_DIR="$TEST_DIRECTORY"/..
 
+# If we were built with ASAN, it may complain about leaks
+# of program-lifetime variables. Disable it by default to lower
+# the noise level. This needs to happen at the start of the script,
+# before we even do our "did we build git yet" check (since we don't
+# want that one to complain to stderr).
+: ${ASAN_OPTIONS=detect_leaks=0}
+export ASAN_OPTIONS
+
 ################################################################
 # It appears that people try to run tests without building...
 "$GIT_BUILD_DIR/git" >/dev/null
@@ -148,9 +156,6 @@ else
 	}
 fi
 
-: ${ASAN_OPTIONS=detect_leaks=0}
-export ASAN_OPTIONS
-
 # Protect ourselves from common misconfiguration to export
 # CDPATH into the environment
 unset CDPATH

-- 
2.13.2.1071.gcd8104b61
Jeff King· Jul 10, 2017, 13:24 UTC · re: Jeff King · lore

[PATCH 3/5] Makefile: add helper for compiling with -fsanitize

You can already build and test with ASan by doing:
  make CFLAGS=-fsanitize=address test
but there are a few slight annoyances:
  1. It's a little long to type.
  2. It override your CFLAGS completely. You'd probably
     still want -O2, for instance.
  3. It's a good idea to also turn off "recovery", which
     lets the program keep running after a problem is
     detected (with the intention of finding as many bugs as
     possible in a given run). Since Git's test suite should
     generally run without triggering any problems, it's
     better to abort immediately and fail the test when we
     do find an issue.

With this patch, all of that happens automatically when you run:

  make SANITIZE=address test
Signed-off-by: Jeff King <peff@peff.net>
---
 Makefile | 4 ++++
 1 file changed, 4 insertions(+)
Show changes to Makefile +4 −0
diff --git a/Makefile b/Makefile
index 9c9c42f8f..59f6bdcd7 100644
--- a/Makefile
+++ b/Makefile
@@ -1012,6 +1012,10 @@ ifdef DEVELOPER
 CFLAGS += $(DEVELOPER_CFLAGS)
 endif
 
+ifdef SANITIZE
+BASIC_CFLAGS += -fsanitize=$(SANITIZE) -fno-sanitize-recover=$(SANITIZE)
+endif
+
 ifndef sysconfdir
 ifeq ($(prefix),/usr)
 sysconfdir = /etc

-- 
2.13.2.1071.gcd8104b61
Junio C Hamano· Jul 10, 2017, 17:35 UTC · re: Jeff King · lore

Re: [PATCH 3/5] Makefile: add helper for compiling with -fsanitize

Jeff King <peff@peff.net> writes:
Show 18 quoted lines
> You can already build and test with ASan by doing:
>
>   make CFLAGS=-fsanitize=address test
>
> but there are a few slight annoyances:
>
>   1. It's a little long to type.
>
>   2. It override your CFLAGS completely. You'd probably
>      still want -O2, for instance.
>
>   3. It's a good idea to also turn off "recovery", which
>      lets the program keep running after a problem is
>      detected (with the intention of finding as many bugs as
>      possible in a given run). Since Git's test suite should
>      generally run without triggering any problems, it's
>      better to abort immediately and fail the test when we
>      do find an issue.

Unfortunately I do not think Comparing between versions in https://gcc.gnu.org/onlinedocs, it appears that -fsanitize-recover is not configurable for folks still with GCC 4.x series, and this patch is not very useful unless you disable the recovery for the purpose of running our tests as you said X-<.

Show 25 quoted lines
> With this patch, all of that happens automatically when you
> run:
>
>   make SANITIZE=address test
>
> Signed-off-by: Jeff King <peff@peff.net>
> ---
>  Makefile | 4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/Makefile b/Makefile
> index 9c9c42f8f..59f6bdcd7 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -1012,6 +1012,10 @@ ifdef DEVELOPER
>  CFLAGS += $(DEVELOPER_CFLAGS)
>  endif
>  
> +ifdef SANITIZE
> +BASIC_CFLAGS += -fsanitize=$(SANITIZE) -fno-sanitize-recover=$(SANITIZE)
> +endif
> +
>  ifndef sysconfdir
>  ifeq ($(prefix),/usr)
>  sysconfdir = /etc
Jeff King· Jul 10, 2017, 17:44 UTC · re: Junio C Hamano · lore

Re: [PATCH 3/5] Makefile: add helper for compiling with -fsanitize

On Mon, Jul 10, 2017 at 10:35:24AM -0700, Junio C Hamano wrote:
Show 26 quoted lines
> Jeff King <peff@peff.net> writes:
> 
> > You can already build and test with ASan by doing:
> >
> >   make CFLAGS=-fsanitize=address test
> >
> > but there are a few slight annoyances:
> >
> >   1. It's a little long to type.
> >
> >   2. It override your CFLAGS completely. You'd probably
> >      still want -O2, for instance.
> >
> >   3. It's a good idea to also turn off "recovery", which
> >      lets the program keep running after a problem is
> >      detected (with the intention of finding as many bugs as
> >      possible in a given run). Since Git's test suite should
> >      generally run without triggering any problems, it's
> >      better to abort immediately and fail the test when we
> >      do find an issue.
> 
> Unfortunately I do not think Comparing between versions in
> https://gcc.gnu.org/onlinedocs, it appears that -fsanitize-recover
> is not configurable for folks still with GCC 4.x series, and this
> patch is not very useful unless you disable the recovery for the
> purpose of running our tests as you said X-<.

I didn't actually dig into the history of gcc support at all. Back in the 4.x time-frame I tried using ASan and couldn't get it to work at all. I ended up just always building with clang (which from my mostly-ignorant view seems to to be the primary platform for ASan development).

Since this is an optional build that doesn't need to be available everywhere, I'd actually be fine with saying "just use clang". But as far as I can tell, gcc seems to work fine these days. I consider this mostly a best-effort tool.

I'm also not sure of the behavior without -fno-sanitize-recover. I think ASan may barf either way. The commit message for my config.mak from a year or two ago claims that the problem was actually with UBSan. It would be useful in the long run for that to work, too.

-Peff
Junio C Hamano· Jul 10, 2017, 18:07 UTC · re: Jeff King · lore

Re: [PATCH 3/5] Makefile: add helper for compiling with -fsanitize

Jeff King <peff@peff.net> writes:
Show 44 quoted lines
> On Mon, Jul 10, 2017 at 10:35:24AM -0700, Junio C Hamano wrote:
>
>> Jeff King <peff@peff.net> writes:
>> 
>> > You can already build and test with ASan by doing:
>> >
>> >   make CFLAGS=-fsanitize=address test
>> >
>> > but there are a few slight annoyances:
>> >
>> >   1. It's a little long to type.
>> >
>> >   2. It override your CFLAGS completely. You'd probably
>> >      still want -O2, for instance.
>> >
>> >   3. It's a good idea to also turn off "recovery", which
>> >      lets the program keep running after a problem is
>> >      detected (with the intention of finding as many bugs as
>> >      possible in a given run). Since Git's test suite should
>> >      generally run without triggering any problems, it's
>> >      better to abort immediately and fail the test when we
>> >      do find an issue.
>> 
>> Unfortunately I do not think Comparing between versions in
>> https://gcc.gnu.org/onlinedocs, it appears that -fsanitize-recover
>> is not configurable for folks still with GCC 4.x series, and this
>> patch is not very useful unless you disable the recovery for the
>> purpose of running our tests as you said X-<.
>
> I didn't actually dig into the history of gcc support at all. Back in
> the 4.x time-frame I tried using ASan and couldn't get it to work at
> all. I ended up just always building with clang (which from my
> mostly-ignorant view seems to to be the primary platform for ASan
> development).
>
> Since this is an optional build that doesn't need to be available
> everywhere, I'd actually be fine with saying "just use clang". But as
> far as I can tell, gcc seems to work fine these days. I consider this
> mostly a best-effort tool.
>
> I'm also not sure of the behavior without -fno-sanitize-recover. I think
> ASan may barf either way. The commit message for my config.mak from a
> year or two ago claims that the problem was actually with UBSan. It
> would be useful in the long run for that to work, too.

Yes. I'd agree with all of the above. While copyediting my response, I somehow ended up removing one paragraph before that "Unfortunately" by accident X-<, but the paragraph said essentially the same "this is optional so it is a strict improvement, and I do agree recovery must be disabled to be useful in our context".

Sorry for a possible confusion.
Ramsay Jones· Jul 10, 2017, 20:02 UTC · re: Jeff King · lore

Re: [PATCH 3/5] Makefile: add helper for compiling with -fsanitize

On 10/07/17 18:44, Jeff King wrote:
Show 44 quoted lines
> On Mon, Jul 10, 2017 at 10:35:24AM -0700, Junio C Hamano wrote:
> 
>> Jeff King <peff@peff.net> writes:
>>
>>> You can already build and test with ASan by doing:
>>>
>>>   make CFLAGS=-fsanitize=address test
>>>
>>> but there are a few slight annoyances:
>>>
>>>   1. It's a little long to type.
>>>
>>>   2. It override your CFLAGS completely. You'd probably
>>>      still want -O2, for instance.
>>>
>>>   3. It's a good idea to also turn off "recovery", which
>>>      lets the program keep running after a problem is
>>>      detected (with the intention of finding as many bugs as
>>>      possible in a given run). Since Git's test suite should
>>>      generally run without triggering any problems, it's
>>>      better to abort immediately and fail the test when we
>>>      do find an issue.
>>
>> Unfortunately I do not think Comparing between versions in
>> https://gcc.gnu.org/onlinedocs, it appears that -fsanitize-recover
>> is not configurable for folks still with GCC 4.x series, and this
>> patch is not very useful unless you disable the recovery for the
>> purpose of running our tests as you said X-<.
> 
> I didn't actually dig into the history of gcc support at all. Back in
> the 4.x time-frame I tried using ASan and couldn't get it to work at
> all. I ended up just always building with clang (which from my
> mostly-ignorant view seems to to be the primary platform for ASan
> development).
> 
> Since this is an optional build that doesn't need to be available
> everywhere, I'd actually be fine with saying "just use clang". But as
> far as I can tell, gcc seems to work fine these days. I consider this
> mostly a best-effort tool.
> 
> I'm also not sure of the behavior without -fno-sanitize-recover. I think
> ASan may barf either way. The commit message for my config.mak from a
> year or two ago claims that the problem was actually with UBSan. It
> would be useful in the long run for that to work, too.

Just FYI, I had a quick look at this tonight. I applied your patches to master, the tried 'make SANITIZE=address test', which worked fine. I then tried 'make SANITIZE=undefined test' and I had to control+C it after nearly two hours on one test! ;-) (somewhere in the t4xxx - unfortunately I overwrote the output file without thinking).

[BTW I am on Linux Mint 18.2 x86_64, gcc version 5.4.0]

After a quick look at the ./t0000-basic.sh test, I managed to get the test to complete (with 15 tests failing), with the following patch applied:

-- >8 --
Show changes to 2 files +5 −1

Makefile, sha1dc/sha1.c

diff --git a/Makefile b/Makefile
index 3c341b2a6..8e6433738 100644
--- a/Makefile
+++ b/Makefile
@@ -1016,7 +1016,7 @@ ifdef SANITIZE
 BASIC_CFLAGS += -fsanitize=$(SANITIZE) -fno-sanitize-recover=$(SANITIZE)
 BASIC_CFLAGS += -fno-omit-frame-pointer
 ifeq ($(SANITIZE),undefined)
-BASIC_CFLAGS += -DNO_UNALIGNED_LOADS
+BASIC_CFLAGS += -DNO_UNALIGNED_LOADS -DSHA1DC_FORCE_ALIGNED_ACCESS
 endif
 endif
 
diff --git a/sha1dc/sha1.c b/sha1dc/sha1.c
index 25eded139..3baddc636 100644
--- a/sha1dc/sha1.c
+++ b/sha1dc/sha1.c
@@ -118,6 +118,10 @@
 #define SHA1DC_ALLOW_UNALIGNED_ACCESS
 #endif /*UNALIGNMENT DETECTION*/
 
+#if defined(SHA1DC_ALLOW_UNALIGNED_ACCESS) && defined(SHA1DC_FORCE_ALIGNED_ACCESS)
+#undef SHA1DC_ALLOW_UNALIGNED_ACCESS
+#endif
+
 
 #define rotate_right(x,n) (((x)>>(n))|((x)<<(32-(n))))
 #define rotate_left(x,n)  (((x)<<(n))|((x)>>(32-(n))))
--------

Hmm, hopefully that is not whitespace damaged.

ATB,
Ramsay Jones
Jeff King· Jul 11, 2017, 04:44 UTC · re: Ramsay Jones · lore

Re: [PATCH 3/5] Makefile: add helper for compiling with -fsanitize

On Mon, Jul 10, 2017 at 09:02:24PM +0100, Ramsay Jones wrote:
Show 17 quoted lines
> After a quick look at the ./t0000-basic.sh test, I managed to get
> the test to complete (with 15 tests failing), with the following
> patch applied:
> 
> -- >8 --
> diff --git a/Makefile b/Makefile
> index 3c341b2a6..8e6433738 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -1016,7 +1016,7 @@ ifdef SANITIZE
>  BASIC_CFLAGS += -fsanitize=$(SANITIZE) -fno-sanitize-recover=$(SANITIZE)
>  BASIC_CFLAGS += -fno-omit-frame-pointer
>  ifeq ($(SANITIZE),undefined)
> -BASIC_CFLAGS += -DNO_UNALIGNED_LOADS
> +BASIC_CFLAGS += -DNO_UNALIGNED_LOADS -DSHA1DC_FORCE_ALIGNED_ACCESS
>  endif
>  endif

Thanks, I forgot to mention SHA1DC. When I had originally tested with "undefined", it was before we had SHA1DC. I hacked around it earlier today by just using OPENSSL_SHA1. ;)

I agree if we can ask it to avoid unaligned access that is even better.
Show 11 quoted lines
> diff --git a/sha1dc/sha1.c b/sha1dc/sha1.c
> index 25eded139..3baddc636 100644
> --- a/sha1dc/sha1.c
> +++ b/sha1dc/sha1.c
> @@ -118,6 +118,10 @@
>  #define SHA1DC_ALLOW_UNALIGNED_ACCESS
>  #endif /*UNALIGNMENT DETECTION*/
>  
> +#if defined(SHA1DC_ALLOW_UNALIGNED_ACCESS) && defined(SHA1DC_FORCE_ALIGNED_ACCESS)
> +#undef SHA1DC_ALLOW_UNALIGNED_ACCESS
> +#endif

I think our current strategy is to avoid touching sha1.c as much as possible. I think we'd prefer a patch to the upstream project to support FORCE_ALIGNED_ACCESS (unfortunately I do not see a way to tweak it using only external defines.

-Peff
Jeff King· Jul 10, 2017, 13:24 UTC · re: Jeff King · lore

[PATCH 2/5] test-lib: turn on ASan abort_on_error by default

By default, ASan will exit with code 1 when it sees an error. This means we'll notice a problem when we expected git to succeed, but not in a test_must_fail block.

Let's ask it to actually raise SIGABRT instead. That will give us a signal death that test_must_fail will notice. As a bonus, it may also leave a coredump, which can be handy for digging into a failure.

Signed-off-by: Jeff King <peff@peff.net>
---
 t/test-lib.sh | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
Show changes to t/test-lib.sh +1 −1
diff --git a/t/test-lib.sh b/t/test-lib.sh
index 961194a50..1b6e53f78 100644
--- a/t/test-lib.sh
+++ b/t/test-lib.sh
@@ -41,7 +41,7 @@ GIT_BUILD_DIR="$TEST_DIRECTORY"/..
 # the noise level. This needs to happen at the start of the script,
 # before we even do our "did we build git yet" check (since we don't
 # want that one to complain to stderr).
-: ${ASAN_OPTIONS=detect_leaks=0}
+: ${ASAN_OPTIONS=detect_leaks=0:abort_on_error=1}
 export ASAN_OPTIONS
 
 ################################################################

-- 
2.13.2.1071.gcd8104b61
Junio C Hamano· Jul 10, 2017, 17:18 UTC · re: Jeff King · lore

Re: [PATCH 2/5] test-lib: turn on ASan abort_on_error by default

Jeff King <peff@peff.net> writes:
Show 8 quoted lines
> By default, ASan will exit with code 1 when it sees an
> error. This means we'll notice a problem when we expected
> git to succeed, but not in a test_must_fail block.
>
> Let's ask it to actually raise SIGABRT instead. That will
> give us a signal death that test_must_fail will notice. As a
> bonus, it may also leave a coredump, which can be handy for
> digging into a failure.
Well thought-out.  Thanks.
Show 18 quoted lines
> Signed-off-by: Jeff King <peff@peff.net>
> ---
>  t/test-lib.sh | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/t/test-lib.sh b/t/test-lib.sh
> index 961194a50..1b6e53f78 100644
> --- a/t/test-lib.sh
> +++ b/t/test-lib.sh
> @@ -41,7 +41,7 @@ GIT_BUILD_DIR="$TEST_DIRECTORY"/..
>  # the noise level. This needs to happen at the start of the script,
>  # before we even do our "did we build git yet" check (since we don't
>  # want that one to complain to stderr).
> -: ${ASAN_OPTIONS=detect_leaks=0}
> +: ${ASAN_OPTIONS=detect_leaks=0:abort_on_error=1}
>  export ASAN_OPTIONS
>  
>  ################################################################
Jeff King· Jul 10, 2017, 13:24 UTC · re: Jeff King · lore

[PATCH 5/5] Makefile: disable unaligned loads with UBSan

The undefined behavior sanitizer complains about unaligned loads, even if they're OK for a particular platform in practice. It's possible that they _are_ a problem, of course, but since it's a known tradeoff the UBSan errors are just noise.

Let's quiet it automatically by building with NO_UNALIGNED_LOADS when SANITIZE=undefined is in use.

Signed-off-by: Jeff King <peff@peff.net>
---
 Makefile | 3 +++
 1 file changed, 3 insertions(+)
Show changes to Makefile +3 −0
diff --git a/Makefile b/Makefile
index cc03b3c95..3c341b2a6 100644
--- a/Makefile
+++ b/Makefile
@@ -1015,6 +1015,9 @@ endif
 ifdef SANITIZE
 BASIC_CFLAGS += -fsanitize=$(SANITIZE) -fno-sanitize-recover=$(SANITIZE)
 BASIC_CFLAGS += -fno-omit-frame-pointer
+ifeq ($(SANITIZE),undefined)
+BASIC_CFLAGS += -DNO_UNALIGNED_LOADS
+endif
 endif
 
 ifndef sysconfdir

-- 
2.13.2.1071.gcd8104b61
René Scharfe· Jul 15, 2017, 17:18 UTC · re: Jeff King · lore

Re: [PATCH 5/5] Makefile: disable unaligned loads with UBSan

Am 10.07.2017 um 15:24 schrieb Jeff King:
Show 28 quoted lines
> The undefined behavior sanitizer complains about unaligned
> loads, even if they're OK for a particular platform in
> practice. It's possible that they _are_ a problem, of
> course, but since it's a known tradeoff the UBSan errors are
> just noise.
> 
> Let's quiet it automatically by building with
> NO_UNALIGNED_LOADS when SANITIZE=undefined is in use.
> 
> Signed-off-by: Jeff King <peff@peff.net>
> ---
>   Makefile | 3 +++
>   1 file changed, 3 insertions(+)
> 
> diff --git a/Makefile b/Makefile
> index cc03b3c95..3c341b2a6 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -1015,6 +1015,9 @@ endif
>   ifdef SANITIZE
>   BASIC_CFLAGS += -fsanitize=$(SANITIZE) -fno-sanitize-recover=$(SANITIZE)
>   BASIC_CFLAGS += -fno-omit-frame-pointer
> +ifeq ($(SANITIZE),undefined)
> +BASIC_CFLAGS += -DNO_UNALIGNED_LOADS
> +endif
>   endif
>   
>   ifndef sysconfdir
Nice, but let's be even nicer!
-- >8 --
Subject: [PATCH] Makefile: allow combining UBSan with other sanitizers

Multiple sanitizers can be specified as a comma-separated list. Set the flag NO_UNALIGNED_LOADS even if UndefinedBehaviorSanitizer is not the only sanitizer to build with.

Signed-off-by: Rene Scharfe <l.s.r@web.de>
---
 Makefile | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)
Show changes to Makefile +6 −1
diff --git a/Makefile b/Makefile
index ba4359ef8d..9b98535a04 100644
--- a/Makefile
+++ b/Makefile
@@ -1022,10 +1022,15 @@ ifdef DEVELOPER
 CFLAGS += $(DEVELOPER_CFLAGS)
 endif
 
+comma := ,
+empty :=
+space := $(empty) $(empty)
+
 ifdef SANITIZE
+SANITIZERS := $(foreach flag,$(subst $(comma),$(space),$(SANITIZE)),$(flag))
 BASIC_CFLAGS += -fsanitize=$(SANITIZE) -fno-sanitize-recover=$(SANITIZE)
 BASIC_CFLAGS += -fno-omit-frame-pointer
-ifeq ($(SANITIZE),undefined)
+ifneq ($(filter undefined,$(SANITIZERS)),)
 BASIC_CFLAGS += -DNO_UNALIGNED_LOADS
 endif
 endif

-- 
2.13.3
Jeff King· Jul 16, 2017, 10:17 UTC · re: René Scharfe · lore

Re: [PATCH 5/5] Makefile: disable unaligned loads with UBSan

On Sat, Jul 15, 2017 at 07:18:56PM +0200, René Scharfe wrote:
Show 6 quoted lines
> -- >8 --
> Subject: [PATCH] Makefile: allow combining UBSan with other sanitizers
> 
> Multiple sanitizers can be specified as a comma-separated list.  Set
> the flag NO_UNALIGNED_LOADS even if UndefinedBehaviorSanitizer is not
> the only sanitizer to build with.
Nice, I didn't know you could do comma-separation here. ;)

I always just built the various sanitizers separately since I was testing whether each one worked. But if we can get UBSan to build cleanly, I agree that "make SANITIZE=address,undefined test" would be a nice thing to run periodically.

Show 18 quoted lines
> diff --git a/Makefile b/Makefile
> index ba4359ef8d..9b98535a04 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -1022,10 +1022,15 @@ ifdef DEVELOPER
>  CFLAGS += $(DEVELOPER_CFLAGS)
>  endif
>  
> +comma := ,
> +empty :=
> +space := $(empty) $(empty)
> +
>  ifdef SANITIZE
> +SANITIZERS := $(foreach flag,$(subst $(comma),$(space),$(SANITIZE)),$(flag))
>  BASIC_CFLAGS += -fsanitize=$(SANITIZE) -fno-sanitize-recover=$(SANITIZE)
>  BASIC_CFLAGS += -fno-omit-frame-pointer
> -ifeq ($(SANITIZE),undefined)
> +ifneq ($(filter undefined,$(SANITIZERS)),)

The implementation is convoluted in the way that "make" usually forces us into. ;)

I would have written it as:
  ifeq ($findstring $(SANITIZERS), undefined), undefined)
but I think your version:
  1. Isn't fooled by superstrings like a potential undefined-foo
     sanitizer.
  2. Handles SANITIZE=undefined,undefined correctly.
Neither are expected, but it doesn't hurt to be a bit more robust.
-Peff
René Scharfe· Jul 16, 2017, 11:02 UTC · re: Jeff King · lore

Re: [PATCH 5/5] Makefile: disable unaligned loads with UBSan

Am 16.07.2017 um 12:17 schrieb Jeff King:
Show 15 quoted lines
> On Sat, Jul 15, 2017 at 07:18:56PM +0200, René Scharfe wrote:
> 
>> -- >8 --
>> Subject: [PATCH] Makefile: allow combining UBSan with other sanitizers
>>
>> Multiple sanitizers can be specified as a comma-separated list.  Set
>> the flag NO_UNALIGNED_LOADS even if UndefinedBehaviorSanitizer is not
>> the only sanitizer to build with.
> 
> Nice, I didn't know you could do comma-separation here. ;)
> 
> I always just built the various sanitizers separately since I was
> testing whether each one worked. But if we can get UBSan to build
> cleanly, I agree that "make SANITIZE=address,undefined test" would be a
> nice thing to run periodically.

There are *some* restrictions: You can only use one of address, memory and thread, as mentioned here:

http://clang.llvm.org/docs/UsersManual.html#controlling-code-generation
Combining ASan and UBSan works fine.
René
Jeff King· Jul 10, 2017, 13:24 UTC · re: Jeff King · lore

[PATCH 4/5] Makefile: turn off -fomit-frame-pointer with sanitizers

The ASan manual recommends disabling this optimization, as it can make the backtraces produced by the tool harder to follow (and since this is a test-debug build, we don't care about squeezing out every last drop of performance).

Signed-off-by: Jeff King <peff@peff.net>
---
 Makefile | 1 +
 1 file changed, 1 insertion(+)
Show changes to Makefile +1 −0
diff --git a/Makefile b/Makefile
index 59f6bdcd7..cc03b3c95 100644
--- a/Makefile
+++ b/Makefile
@@ -1014,6 +1014,7 @@ endif
 
 ifdef SANITIZE
 BASIC_CFLAGS += -fsanitize=$(SANITIZE) -fno-sanitize-recover=$(SANITIZE)
+BASIC_CFLAGS += -fno-omit-frame-pointer
 endif
 
 ifndef sysconfdir

-- 
2.13.2.1071.gcd8104b61
Jeff King· Jul 10, 2017, 13:30 UTC · re: Jeff King · lore

Re: [PATCH 0/5] building git with clang/gcc address sanitizer

On Mon, Jul 10, 2017 at 09:24:18AM -0400, Jeff King wrote:
Show 7 quoted lines
> You can also try:
> 
>   make SANITIZE=thread test
> 
> but it's not clean. I poked at some of the errors, and I don't think
> there a problem in practice (though they may be worth cleaning up in the
> name of code hygiene).

Here's an example that I fixed up long ago, but never quite had the stomach to seriously propose.

If it were the last one, it might be worth applying to get a clean run of "make test", but I think it's just one of many.

-- >8 --
Date: Mon, 8 Dec 2014 03:02:34 -0500
Subject: [PATCH] transport-helper: initialize debug flag before starting
 threads

The transport_debug() function uses a static variable to lazily cache the boolean value of $TRANSPORT_DEBUG. If a program uses transport-helper's bidirectional_transfer_loop (as remote-ext and remote-fd do), then two threads may both try to write the variable at the same time.

We can fix this by initializing the variable right before starting the threads.

Noticed by "-fsanitize=thread". This probably isn't a problem in practice, as both threads will write the same value, and we are unlikely to see a torn write on an "int" (i.e., on sane platforms a write to an int is atomic).

Signed-off-by: Jeff King <peff@peff.net>
---
 transport-helper.c | 18 ++++++++++++++----
 1 file changed, 14 insertions(+), 4 deletions(-)
Show changes to transport-helper.c +14 −4
diff --git a/transport-helper.c b/transport-helper.c
index 33cff38cc..76f19ddb0 100644
--- a/transport-helper.c
+++ b/transport-helper.c
@@ -1113,17 +1113,23 @@ int transport_helper_init(struct transport *transport, const char *name)
 /* This should be enough to hold debugging message. */
 #define PBUFFERSIZE 8192
 
+static int transport_debug_enabled(void)
+{
+	static int debug_enabled = -1;
+
+	if (debug_enabled < 0)
+		debug_enabled = getenv("GIT_TRANSLOOP_DEBUG") ? 1 : 0;
+	return debug_enabled;
+}
+
 /* Print bidirectional transfer loop debug message. */
 __attribute__((format (printf, 1, 2)))
 static void transfer_debug(const char *fmt, ...)
 {
 	va_list args;
 	char msgbuf[PBUFFERSIZE];
-	static int debug_enabled = -1;
 
-	if (debug_enabled < 0)
-		debug_enabled = getenv("GIT_TRANSLOOP_DEBUG") ? 1 : 0;
-	if (!debug_enabled)
+	if (!transport_debug_enabled())
 		return;
 
 	va_start(args, fmt);
@@ -1292,6 +1298,10 @@ static int tloop_spawnwait_tasks(struct bidirectional_transfer_state *s)
 	pthread_t ptg_thread;
 	int err;
 	int ret = 0;
+
+	/* initialize static global debug flag as a side effect */
+	transport_debug_enabled();
+
 	err = pthread_create(&gtp_thread, NULL, udt_copy_task_routine,
 		&s->gtp);
 	if (err)

-- 
2.13.2.1071.gcd8104b61
Lars Schneider· Jul 10, 2017, 14:40 UTC · re: Jeff King · lore

Re: [PATCH 0/5] building git with clang/gcc address sanitizer

Show 21 quoted lines
> On 10 Jul 2017, at 15:24, Jeff King <peff@peff.net> wrote:
> 
> I mentioned recently that I sometimes run the test suite with ASan, so
> here are a few tweaks to make this easier (most of which I've been
> carrying in my personal config.mak for a few years).
> 
> In my experience ASan does at least as well as valgrind at finding
> memory bugs, and runs way faster. With this series, running:
> 
>  make SANITIZE=address test
> 
> takes about 4.5 minutes on my machine. A normal build+test is about 1.5
> minutes on the same machine. I haven't timed a full run with --valgrind
> recently, but I know that it is much much slower. :)
> 
> If you want to see it in action, you can do:
> 
>  make SANITIZE=address
>  ./git log -g HEAD HEAD >/dev/null
> 
> which finds a bug I recently fixed (but the fix isn't in master yet).

Do you think it would make sense to run these sanitizers on TravisCI to ensure they keep clean? If yes, should we run only "address" or all of them (if they run clean)?

- Lars
Show 50 quoted lines
> 
> There are other sanitizers, too. I _thought_ I had
> 
>  make SANITIZE=undefined test
> 
> running cleanly at one point, but it's definitely not clean now. Patch 5
> helps a little by disabling unaligned loads in our get_be32() macros.
> Once upon a time I had to set INTERNAL_QSORT, but it isn't necessary
> anymore since everything goes through sane_qsort(). Most of the
> remaining bugs are of a similar form, doing something like:
> 
>  memcpy(NULL, NULL, 0);
> 
> I don't know if it's worth having a sane_memcpy() there, or simply
> tweaking the code to avoid the call (almost all of them are a single
> call from apply.c:2870).
> 
> It looks like we also have a case of shifting off the left side of a
> signed int, which is undefined.
> 
> You can also try:
> 
>  make SANITIZE=thread test
> 
> but it's not clean. I poked at some of the errors, and I don't think
> there a problem in practice (though they may be worth cleaning up in the
> name of code hygiene).
> 
> There's also:
> 
>  make SANITIZE=memory test
> 
> This is clang-only. It's supposed to find uses of uninitialized memory.
> But it complains about writing out anything that zlib has touched. I
> seem to recall that valgrind had a similar problem. I'm not sure what
> zlib does to confuse these analyzers. For valgrind we were able to add a
> suppression. We could probably do the same here, but I haven't looked
> into it.
> 
>  [1/5]: test-lib: set ASAN_OPTIONS variable before we run git
>  [2/5]: test-lib: turn on ASan abort_on_error by default
>  [3/5]: Makefile: add helper for compiling with -fsanitize
>  [4/5]: Makefile: turn off -fomit-frame-pointer with sanitizers
>  [5/5]: Makefile: disable unaligned loads with UBSan
> 
> Makefile      |  8 ++++++++
> t/test-lib.sh | 11 ++++++++---
> 2 files changed, 16 insertions(+), 3 deletions(-)
> 
> -Peff
Jeff King· Jul 10, 2017, 15:58 UTC · re: Lars Schneider · lore

Re: [PATCH 0/5] building git with clang/gcc address sanitizer

On Mon, Jul 10, 2017 at 04:40:42PM +0200, Lars Schneider wrote:
Show 10 quoted lines
> > If you want to see it in action, you can do:
> > 
> >  make SANITIZE=address
> >  ./git log -g HEAD HEAD >/dev/null
> > 
> > which finds a bug I recently fixed (but the fix isn't in master yet).
> 
> Do you think it would make sense to run these sanitizers on TravisCI
> to ensure they keep clean? If yes, should we run only "address" or all
> of them (if they run clean)?

Maybe. It's expensive and it's relatively rare that it catches anything. I used to run valgrind (which is even more expensive) once every release or so. This is much cheaper, but I've noticed that the Travis environment is a lot slower than my laptop. So it might take an hour to run there, which I think would trigger some timeouts?

I guess the best way is to try it and see. I probably wouldn't do an ASan run for each environment, but just one Linux ASan run, due to the CPU expense. (TBH, I think the existing gcc versus clang on both platforms is already slight overkill. But I guess if we have CPU to burn, more coverage is better than less).

I think "address" is the only one that runs clean right now. With some work I think we could get "undefined" to run clean. The others, I'm not so sure.

Some of them can actually be combined in a single build, but I'd have to dig into the documentation to see which (I think "thread" and "address" don't work well together, but "undefined" and "address" might). My SANITIZE trick doesn't handle multiple entries, but it could probably be taught to.

-Peff

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