[LLVMdev] compiler-rt with MSVC 2013

Aaron Ballman aaron at aaronballman.com
Thu Oct 23 12:38:29 PDT 2014

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:
>>>> -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

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
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

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.


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