[cfe-commits] r169328 - in /cfe/trunk: lib/Driver/Tools.cpp test/Driver/asan-ld.c
Kostya Serebryany
kcc at google.com
Wed Dec 5 05:24:34 PST 2012
On Wed, Dec 5, 2012 at 1:30 PM, Evgeniy Stepanov <eugenis at google.com> wrote:
> We could reimplement the __cxa_guard_* stuff in TSan...
>
Dmitry did this in r169376.
We still have a similar problem in asan with __cxa_throw (less likely to
appear in real life, but still possible).
--kcc
>
>
> On Wed, Dec 5, 2012 at 12:47 PM, Kostya Serebryany <kcc at google.com> wrote:
>
>> And with tsan the situation is worse because it has to
>> intercept __cxa_guard_acquire/__cxa_guard_release,
>>
>>
>> On Wed, Dec 5, 2012 at 12:45 PM, Kostya Serebryany <kcc at google.com>wrote:
>>
>>>
>>>
>>> On Wed, Dec 5, 2012 at 12:36 PM, Chandler Carruth <chandlerc at gmail.com>wrote:
>>>
>>>> On Wed, Dec 5, 2012 at 12:13 AM, Kostya Serebryany <kcc at google.com>wrote:
>>>>
>>>>> +asan/tsan/msan folks
>>>>>
>>>>> That's not as simple as this, I afraid.
>>>>> In *san there are two different kinds of interceptors.
>>>>> 1. foo from libc/libstc++ is completely replaced with foo from asan.
>>>>> Example: malloc, operator new
>>>>> 2. foo from libc/libstc++ is wrapped, such that when a user calls foo
>>>>> it calls the asan copy, but then the asan function calls the original foo.
>>>>> Example: pthread_create, __cxa_throw
>>>>>
>>>>> This change allows to use -static-libstdc++ with asan w/o link
>>>>> failures, but asan is still broken for -static-libstdc++ in a subtle way
>>>>> (since the __cxa_throw is not intercepted, asan will have rare false
>>>>> positives in presence of exceptions).
>>>>>
>>>>
>>>> Can you describe the rare false positive? What would be needed to fully
>>>> fix this?
>>>>
>>>
>>> __cxa_throw is unfriendly to asan as it never returns from the current
>>> function.
>>> If there is poisoned stack it will neve get unpoisoned after throw. Some
>>> one else later will step on the poisoned stack and get a false positive.
>>> This is why we
>>> 1. Intercept __cxa_throw and call __asan_handle_no_return
>>> (asan/asan_interceptors.cc)
>>> 2. We also call __asan_handle_no_return before any noreturn call when
>>> we instrument it.
>>>
>>> Today if you use -static-libstdc++ the asan's __cxa_throw interceptor
>>> is not called.
>>> So, if a throw happens in a code that we don't instrument, we will not
>>> call __asan_handle_no_return at all. Booom.
>>>
>>>
>>>
>>>
>>>>
>>>>
>>>>> Tsan also intercepts __cxa_guard in the similar way, so it will have
>>>>> false positives on function scope statics.
>>>>>
>>>>> Do we really care that much about linking asan with static libstdc++?
>>>>>
>>>>
>>>> In my opinion, yes. We already have too much that is special about
>>>> linking with asan....
>>>>
>>>
>>> Well, yes. E.g. it does not support fully static linking at all, and
>>> hardly ever will.
>>>
>>> --kcc
>>>
>>>
>>>
>>>>
>>>>
>>>>>
>>>>> --kcc
>>>>>
>>>>>
>>>>> On Wed, Dec 5, 2012 at 2:54 AM, Chandler Carruth <chandlerc at gmail.com>wrote:
>>>>>
>>>>>> Author: chandlerc
>>>>>> Date: Tue Dec 4 16:54:37 2012
>>>>>> New Revision: 169328
>>>>>>
>>>>>> URL: http://llvm.org/viewvc/llvm-project?rev=169328&view=rev
>>>>>> Log:
>>>>>> Add -whole-archive around the ASan runtime archive in the link
>>>>>> command.
>>>>>>
>>>>>> This ensures that even though it comes first, we pick up its .o files.
>>>>>> Note that if we can use this (or something similar / equivalent) on
>>>>>> other platforms, we could potentially remove
>>>>>> ReplaceOperatorsNewAndDelete from the ASan runtimes.
>>>>>>
>>>>>> We should probably do something similar for TSan and MSan as well.
>>>>>>
>>>>>> Modified:
>>>>>> cfe/trunk/lib/Driver/Tools.cpp
>>>>>> cfe/trunk/test/Driver/asan-ld.c
>>>>>>
>>>>>> Modified: cfe/trunk/lib/Driver/Tools.cpp
>>>>>> URL:
>>>>>> http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Driver/Tools.cpp?rev=169328&r1=169327&r2=169328&view=diff
>>>>>>
>>>>>> ==============================================================================
>>>>>> --- cfe/trunk/lib/Driver/Tools.cpp (original)
>>>>>> +++ cfe/trunk/lib/Driver/Tools.cpp Tue Dec 4 16:54:37 2012
>>>>>> @@ -1524,8 +1524,14 @@
>>>>>> // The ASan runtime needs to come before -lstdc++ (or -lc++,
>>>>>> libstdc++.a,
>>>>>> // etc.) so that the linker picks ASan's versions of the
>>>>>> global 'operator
>>>>>> // new' and 'operator delete' symbols. We take the extreme
>>>>>> (but simple)
>>>>>> - // strategy of inserting it at the front of the link command.
>>>>>> - CmdArgs.insert(CmdArgs.begin(), Args.MakeArgString(LibAsan));
>>>>>> + // strategy of inserting it at the front of the link command.
>>>>>> It also
>>>>>> + // needs to be forced to end up in the executable, so wrap it
>>>>>> in
>>>>>> + // whole-archive.
>>>>>> + SmallVector<const char*, 3> PrefixArgs;
>>>>>> + PrefixArgs.push_back("-whole-archive");
>>>>>> + PrefixArgs.push_back(Args.MakeArgString(LibAsan));
>>>>>> + PrefixArgs.push_back("-no-whole-archive");
>>>>>> + CmdArgs.insert(CmdArgs.begin(), PrefixArgs.begin(),
>>>>>> PrefixArgs.end());
>>>>>> CmdArgs.push_back("-lpthread");
>>>>>> CmdArgs.push_back("-ldl");
>>>>>> CmdArgs.push_back("-export-dynamic");
>>>>>>
>>>>>> Modified: cfe/trunk/test/Driver/asan-ld.c
>>>>>> URL:
>>>>>> http://llvm.org/viewvc/llvm-project/cfe/trunk/test/Driver/asan-ld.c?rev=169328&r1=169327&r2=169328&view=diff
>>>>>>
>>>>>> ==============================================================================
>>>>>> --- cfe/trunk/test/Driver/asan-ld.c (original)
>>>>>> +++ cfe/trunk/test/Driver/asan-ld.c Tue Dec 4 16:54:37 2012
>>>>>> @@ -19,7 +19,7 @@
>>>>>> //
>>>>>> // CHECK-LINUX-CXX: "{{.*}}ld{{(.exe)?}}"
>>>>>> // CHECK-LINUX-CXX-NOT: "-lc"
>>>>>> -// CHECK-LINUX-CXX: libclang_rt.asan-i386.a"
>>>>>> +// CHECK-LINUX-CXX: "-whole-archive" "{{.*}}libclang_rt.asan-i386.a"
>>>>>> "-no-whole-archive"
>>>>>> // CHECK-LINUX-CXX: "-lpthread"
>>>>>> // CHECK-LINUX-CXX: "-ldl"
>>>>>> // CHECK-LINUX-CXX: "-export-dynamic"
>>>>>> @@ -32,7 +32,7 @@
>>>>>> //
>>>>>> // CHECK-LINUX-CXX-STATIC: "{{.*}}ld{{(.exe)?}}"
>>>>>> // CHECK-LINUX-CXX-STATIC-NOT: stdc++
>>>>>> -// CHECK-LINUX-CXX-STATIC: libclang_rt.asan-i386.a"
>>>>>> +// CHECK-LINUX-CXX-STATIC: "-whole-archive"
>>>>>> "{{.*}}libclang_rt.asan-i386.a" "-no-whole-archive"
>>>>>> // CHECK-LINUX-CXX-STATIC: stdc++
>>>>>>
>>>>>> // RUN: %clang -no-canonical-prefixes %s -### -o %t.o 2>&1 \
>>>>>>
>>>>>>
>>>>>> _______________________________________________
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>>>>>>
>>>>>
>>>>>
>>>>> _______________________________________________
>>>>> cfe-commits mailing list
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>>>>>
>>>>>
>>>>
>>>
>>
>
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