[cfe-commits] r169328 - in /cfe/trunk: lib/Driver/Tools.cpp test/Driver/asan-ld.c

[Dmitry Vyukov]

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?

Stack shadow won't be unpoisoned in presence of exceptions.
We need to intercept __cxa_throw... which is impossible with static libstdc++.


>> 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....
>
>>
>>
>> --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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