llvm dev - Sep 2015 - Heads up: Bug in CMake found when attempting 64-bit build with 32-bit clang-cl.

Hi Nico, Hans, Takumi,

I made it to the bottom of the issue. Turns out that
CMAKE_C_FLAGS=-m64
CMAKE_CXX_FLAGS=-m64
CMAKE_EXE_LINKER_FLAGS=/machine:x64
is enough to do a 64-bit build correctly with a 32-bit clang-cl (i.e. one
that targets 32-bit by default). Hooray! The missing piece that I had to
track down is why I would see `deps = msvc` stuff spewing onto my terminal,
rather than consumed properly by ninja. I noticed that in rules.ninja,
CMake had generated:

msvc_deps_prefix = LINK : error LNK2001:

After some hunting in procmon, I found that there was a call to clang-cl
done during the configure process that *wasn't including -m64*, leading to
a link error. The text of the link error was then being interpreted as a
valid output for setting msvc_deps_prefix.

Attached is a quick hack patch for CMake that fixes the issue for me
locally. Some more details are in the commit message for the patch. It's
not ideal by any means... my CMake-fu is weak.

Brad, you seem to be roughly our liaison with the CMake community. Do you
know what the next steps are for getting this fixed in CMake upstream?

-- Sean Silva
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btw, Hans, Nico: I noticed that we are using a different triple with
`llvm37_32bit/bin/clang-cl.exe -m64` vs `llvm37_64bit/bin/clang-cl.exe`.

http://i.imgur.com/eJXf2XN.png
The `llvm37_32bit/bin/clang-cl.exe -m64` side of the diff is red; the
`llvm37_64bit/bin/clang-cl.exe` side is in green.
The primary difference seems to be:
`llvm37_32bit/bin/clang-cl.exe -m64` chooses `-triple
x86_64-pc-windows-msvc18.0.0`
`llvm37_64bit/bin/clang-cl.exe` chooses `-triple
x86_64-w64-windows-msvc18.0.0`

Not sure if this is intended behavior or not, but just thought I'd let you
guys know, since from what you guys were saying in IRC it sounded like
`llvm37_32bit/bin/clang-cl.exe -m64` is supposed to be equivalent to
`llvm37_64bit/bin/clang-cl.exe`. Like I said, I managed to get it building
with the settings in the OP, so the difference is not a big deal it seems.

-- Sean SIlva

On Thu, Sep 17, 2015 at 9:07 PM, Sean Silva <chisophugis at gmail.com>
wrote:
> Hi Nico, Hans, Takumi,
>
> I made it to the bottom of the issue. Turns out that
> CMAKE_C_FLAGS=-m64
> CMAKE_CXX_FLAGS=-m64
> CMAKE_EXE_LINKER_FLAGS=/machine:x64
> is enough to do a 64-bit build correctly with a 32-bit clang-cl (i.e. one
> that targets 32-bit by default). Hooray! The missing piece that I had to
> track down is why I would see `deps = msvc` stuff spewing onto my terminal,
> rather than consumed properly by ninja. I noticed that in rules.ninja,
> CMake had generated:
>
> msvc_deps_prefix = LINK : error LNK2001:
>
> After some hunting in procmon, I found that there was a call to clang-cl
> done during the configure process that *wasn't including -m64*, leading
to
> a link error. The text of the link error was then being interpreted as a
> valid output for setting msvc_deps_prefix.
>
> Attached is a quick hack patch for CMake that fixes the issue for me
> locally. Some more details are in the commit message for the patch.
It's
> not ideal by any means... my CMake-fu is weak.
>
> Brad, you seem to be roughly our liaison with the CMake community. Do you
> know what the next steps are for getting this fixed in CMake upstream?
>
> -- Sean Silva
>
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> The `llvm37_32bit/bin/clang-cl.exe -m64` side of the diff is red; the
`llvm37_64bit/bin/clang-cl.exe` side is in green.
> The primary difference seems to be:
> `llvm37_32bit/bin/clang-cl.exe -m64` chooses `-triple
x86_64-pc-windows-msvc18.0.0`
> `llvm37_64bit/bin/clang-cl.exe` chooses `-triple
x86_64-w64-windows-msvc18.0.0`
>
> Not sure if this is intended behavior or not, but just thought I'd let
you guys know,
> since from what you guys were saying in IRC it sounded like
`llvm37_32bit/bin/clang-cl.exe -m64`
> is supposed to be equivalent to `llvm37_64bit/bin/clang-cl.exe`. Like I
said, I managed to get it
> building with the settings in the OP, so the difference is not a big deal
it seems.
What's the default triple for llvm37_32bit/bin/clang-cl.exe? –m64 strips the
CPU/Arch part of the triple and replaces it with 'x86_64' so I expect
the 32-bit triple is something like i586-pc-windows-msvc18.0.0.

I don't see any references to Triple::PC (aside from TripleTest.cpp) and
'w64' looks like it parses as Triple::UnknownVendor so it doesn't
seem to make any functional difference to most of the LLVM projects. Is anyone
aware of functional differences between the 'pc' and 'w64'
vendors in other toolchains?

From: cfe-dev [mailto:cfe-dev-bounces at lists.llvm.org] On Behalf Of Sean Silva
via cfe-dev
Sent: 18 September 2015 05:23
To: llvm-dev; cfe-dev at lists.llvm.org; Hans Wennborg; Nico Weber; Takumi
NAKAMURA; brad.king at kitware.com
Subject: Re: [cfe-dev] Heads up: Bug in CMake found when attempting 64-bit build
with 32-bit clang-cl.

btw, Hans, Nico: I noticed that we are using a different triple with
`llvm37_32bit/bin/clang-cl.exe -m64` vs `llvm37_64bit/bin/clang-cl.exe`.

http://i.imgur.com/eJXf2XN.png
The `llvm37_32bit/bin/clang-cl.exe -m64` side of the diff is red; the
`llvm37_64bit/bin/clang-cl.exe` side is in green.
The primary difference seems to be:
`llvm37_32bit/bin/clang-cl.exe -m64` chooses `-triple
x86_64-pc-windows-msvc18.0.0`
`llvm37_64bit/bin/clang-cl.exe` chooses `-triple x86_64-w64-windows-msvc18.0.0`

Not sure if this is intended behavior or not, but just thought I'd let you
guys know, since from what you guys were saying in IRC it sounded like
`llvm37_32bit/bin/clang-cl.exe -m64` is supposed to be equivalent to
`llvm37_64bit/bin/clang-cl.exe`. Like I said, I managed to get it building with
the settings in the OP, so the difference is not a big deal it seems.

-- Sean SIlva

On Thu, Sep 17, 2015 at 9:07 PM, Sean Silva <chisophugis at
gmail.com<mailto:chisophugis at gmail.com>> wrote:
Hi Nico, Hans, Takumi,

I made it to the bottom of the issue. Turns out that
CMAKE_C_FLAGS=-m64
CMAKE_CXX_FLAGS=-m64
CMAKE_EXE_LINKER_FLAGS=/machine:x64
is enough to do a 64-bit build correctly with a 32-bit clang-cl (i.e. one that
targets 32-bit by default). Hooray! The missing piece that I had to track down
is why I would see `deps = msvc` stuff spewing onto my terminal, rather than
consumed properly by ninja. I noticed that in rules.ninja, CMake had generated:

msvc_deps_prefix = LINK : error LNK2001:

After some hunting in procmon, I found that there was a call to clang-cl done
during the configure process that *wasn't including -m64*, leading to a link
error. The text of the link error was then being interpreted as a valid output
for setting msvc_deps_prefix.

Attached is a quick hack patch for CMake that fixes the issue for me locally.
Some more details are in the commit message for the patch. It's not ideal by
any means... my CMake-fu is weak.

Brad, you seem to be roughly our liaison with the CMake community. Do you know
what the next steps are for getting this fixed in CMake upstream?

-- Sean Silva

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On 09/18/2015 12:07 AM, Sean Silva wrote:
> msvc_deps_prefix = LINK : error LNK2001: 
> 
> there was a call to clang-cl done during the configure process
> that *wasn't including -m64*
This looks like the same problem reported here:

 CMakeClDeps.cmake doesn't work if CC contains arguments
 http://www.cmake.org/Bug/view.php?id=15596

I've just drafted some changes to fix it.  Please follow the issue
tracker entry for details.  Also please try out the fix and report
back.

Thanks,
-Brad

On Fri, Sep 18, 2015 at 7:14 AM, Brad King <brad.king at kitware.com>
wrote:
> On 09/18/2015 12:07 AM, Sean Silva wrote:
> > msvc_deps_prefix = LINK : error LNK2001:
> >
> > there was a call to clang-cl done during the configure process
> > that *wasn't including -m64*
>
> This looks like the same problem reported here:
>
>  CMakeClDeps.cmake doesn't work if CC contains arguments
>  http://www.cmake.org/Bug/view.php?id=15596

D'oh, I should have googled for `msvc_deps_prefix = LINK : error LNK2001: `!

>
> I've just drafted some changes to fix it.  Please follow the issue
> tracker entry for details.  Also please try out the fix and report
> back.
>
I just tried with the `next` branch and it works! Thanks!

-- Sean Silva

>
> Thanks,
> -Brad
>
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