[cfe-commits] r169328 - in /cfe/trunk: lib/Driver/Tools.cpp test/Driver/asan-ld.c
Kostya Serebryany
kcc at google.com
Wed Dec 5 00:47:04 PST 2012
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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>>>
>>>
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>>
>
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