[LLVMdev] compiler-rt with MSVC 2013

[Aaron Ballman]

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