[LLVMdev] compiler-rt with MSVC 2013

Thu Oct 23 13:35:33 PDT 2014

On Thu, Oct 23, 2014 at 3:59 PM, Timur Iskhodzhanov <timurrrr at google.com> wrote:
> compiler-rt libs must be built with /MT, so the MSVS build is doing
> the wrong thing here.

Tada! Fixed in r220506 -- we weren't setting the build flags properly
for *all* targets, just some of them. I was building RelWithDebInfo

~Aaron
>
> 2014-10-23 12:52 GMT-07:00 Aaron Ballman <aaron at aaronballman.com>:
>> On Thu, Oct 23, 2014 at 3:42 PM, Aaron Ballman <aaron at aaronballman.com> wrote:
>>> On Thu, Oct 23, 2014 at 3:38 PM, Aaron Ballman <aaron at aaronballman.com> wrote:
>>>> On Thu, Oct 23, 2014 at 2:57 PM, Aaron Ballman <aaron at aaronballman.com> wrote:
>>>>> On Thu, Oct 23, 2014 at 2:46 PM, Timur Iskhodzhanov <timurrrr at google.com> wrote:
>>>>>> 2014-10-23 11:34 GMT-07:00 Aaron Ballman <aaron at aaronballman.com>:
>>>>>>> On Thu, Oct 23, 2014 at 2:24 PM, Timur Iskhodzhanov <timurrrr at google.com> wrote:
>>>>>>>> I don't think this is the right approach.
>>>>>>>>
>>>>>>>> Currently we intentionally define malloc etc without changing the
>>>>>>>> names and (when stuff works ok) the linker just links all the mem
>>>>>>>> allocator calls with calls to our RTL.  This is kind of a link-time
>>>>>>>> interception.
>>>>>>>
>>>>>>> How could that work in the presence of also having the MSVC CRT
>>>>>>> libraries linked in? When the linker finds the duplicate definition of
>>>>>>> any of those functions, it will produce that link error. You can use
>>>>>>> /FORCE:multiple to work around that, but then any usage of free()
>>>>>>> within compiler-rt is liable to find the asan definition.
>>>>>>
>>>>>> I don't know, it just worked :)
>>>>>
>>>>> LoL, not a vote of confidence. ;-)
>>>>>
>>>>>>
>>>>>>>> I'm not 100% sure off the top of my head but I think __asan_init is
>>>>>>>> explicitly called from the CRT init code later than calloc gets
>>>>>>>> called() from CRT.  To handle everything correctly, calloc() must be
>>>>>>>> "statically" intercepted before __asan_init is called from the CRT
>>>>>>>> (hence before "dynamic" interceptors are set up).
>>>>>>>>
>>>>>>>> Can you please compare what happens in your build configuration compared to:
>>>>>>>> $ cmake -GNinja -DLLVM_ENABLE_ASSERTIONS=ON -DCMAKE_BUILD_TYPE=Release
>>>>>>>> -DLLVM_TARGETS_TO_BUILD=X86 .. && ninja
>>>>>>>> instead?
>>>>>>>
>>>>>>> Do I need something special to support ninja?
>>>>>>
>>>>>> Put it onto your PATH?
>>>>>> e.g. you can
>>>>>> $ svn export http://src.chromium.org/svn/trunk/tools/depot_tools/ninja.exe
>>>>>> and put it into your cmake/bin
>>>>>
>>>>> That worked, and it does compile. I know basically nothing about
>>>>> ninja... is there a way to see what flags it passes to link.exe?
>>>>
>>>> I've found a way to check the linker output from the two builds, and
>>>> they are different.
>>>>
>>>> From the ninja build, with /VERBOSE passed to the linker:
>>>>
>>>>     Searching D:\Program Files (x86)\Microsoft Visual Studio
>>>> 12.0\VC\LIB\LIBCMT.lib:
>>>> ...
>>>>
>>>> At the same stage of linking, from the MSVC build, with /VERBOSE
>>>> passed to the linker:
>>>>
>>>> 2>      Searching D:\Program Files (x86)\Microsoft Visual Studio
>>>> 12.0\VC\lib\MSVCRT.lib:
>>>> ...
>>>> 2>        Found __imp__free
>>>> 2>          Referenced in MSVCRT.lib(crtdll.obj)
>>>> 2>          Loaded MSVCRT.lib(MSVCR120.dll)
>>>> 2>MSVCRT.lib(MSVCR120.dll) : error LNK2005: _free already defined in
>>>> asan_malloc_win.obj
>>>> ...
>>>>
>>>> The ninja build has:
>>>>  Processed /DISALLOWLIB:libcmtd.lib
>>>>  Processed /DISALLOWLIB:msvcrt.lib
>>>>  Processed /DISALLOWLIB:msvcrtd.lib
>>>>
>>>> The MSVC build has:
>>>> 2>  Processed /DEFAULTLIB:kernel32.lib
>>>> 2>   Processed /DISALLOWLIB:libcmt.lib
>>>> 2>   Processed /DISALLOWLIB:libcmtd.lib
>>>> 2>   Processed /DISALLOWLIB:msvcrtd.lib
>>>>
>>>> So the two builds are not equivalent; the ninja build is somehow
>>>> disallowing msvcrt.lib while the MSVC build is not.
>>>
>>> I should note that libcmt.lib is what you get with /MT, and msvcrt.lib
>>> is what you get with /MD. I do not understand why Ninja seems to have
>>> the libraries associated with /MT when linking the DLL ([100/100]
>>> Linking CXX shared library lib\asan\clang_rt.asan_dynamic-i386.dll is
>>> where I pulled those lines from).
>>
>> I think I figured out the issue. From the build.ninja file, I found:
>>
>> build lib\asan\CMakeFiles\RTAsan_dynamic.i386.dir\asan_malloc_win.cc.obj:
>> CXX_COMPILER E$:\llvm\compiler-rt\lib\asan\asan_malloc_win.cc
>>   DEFINES = -DASAN_DYNAMIC=1 -DASAN_HAS_EXCEPTIONS=1
>> -DINTERCEPTION_DYNAMIC_CRT -D__func__=__FUNCTION__
>>   DEP_FILE = lib/asan/CMakeFiles/RTAsan_dynamic.i386.dir/asan_malloc_win.cc.obj.d
>>   FLAGS = /DWIN32 /D_WINDOWS /W3 /GR /EHsc /W3 /MT /O2 /Ob2 /D NDEBUG
>> -IE:\llvm\compiler-rt\lib\asan\..     /machine:X86   /DWIN32
>> /D_WINDOWS /W3 /GR /EHsc /W3 /Oy- /GS- /VERBOSE /Zi /wd4391 /wd4722
>> /wd4291 /wd4800 /GR- /DEBUG
>>   OBJECT_DIR = lib\asan\CMakeFiles\RTAsan_dynamic.i386.dir
>>   TARGET_PDB = ""
>>
>> Notice how it's passing the /MT flag instead of /MD? That's different
>> from MSVC, which is using this for its command line options:
>>
>> /GS- /TP /analyze- /W3 /wd"4391" /wd"4722" /wd"4291" /wd"4800"
>> /Zc:wchar_t /I"E:\llvm\compiler-rt\lib\asan\.." /Zi /Gm- /O2 /Ob1
>> /Fd"RTAsan_dynamic.i386.dir\RelWithDebInfo\vc120.pdb" /fp:precise /D
>> "WIN32" /D "_WINDOWS" /D "NDEBUG" /D "EBUG" /D "ASAN_HAS_EXCEPTIONS=1"
>> /D "ASAN_DYNAMIC=1" /D "INTERCEPTION_DYNAMIC_CRT" /D
>> "__func__=__FUNCTION__" /D "CMAKE_INTDIR=\"RelWithDebInfo\"" /D
>> "_MBCS" /errorReport:prompt /WX- /Zc:forScope /GR- /Gd /Oy- /MD
>> /Fa"RelWithDebInfo/" /EHsc /nologo
>> /Fo"RTAsan_dynamic.i386.dir\RelWithDebInfo\"
>> /Fp"RTAsan_dynamic.i386.dir\RelWithDebInfo\RTAsan_dynamic.i386.pch"
>>
>> (Note how it uses /MD)
>>
>> So, basically, ninja is linking as though everything was being
>> compiled for a static library, when we're actually building a DLL
>> (from what I can tell, anyway).
>>
>> ~Aaron