[LLVMdev] compiler-rt with MSVC 2013

[Timur Iskhodzhanov]

compiler-rt libs must be built with /MT, so the MSVS build is doing
the wrong thing here.

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