[LLVMdev] [RFC PATCH] X32 ABI support for Clang/compiler-rt (compiler-rt patch)

[Alexey Samsonov]

On Thu, Aug 22, 2013 at 11:39 AM, Steven Newbury <steve at snewbury.org.uk>wrote:

> On Thu, 2013-08-22 at 11:27 +0400, Alexey Samsonov wrote:
> > Hi Steven,
> >
> > This looks interesting and raises a number of questions :)
> >
> > 1) Does applying this patch actually bring working sanitizers to x32
> > platform?
> > That is, after you build the clang, does "clang -fsanitize=whatever
> foo.c"
> > compile/link/run with expected results?
> > I doubt that, as there is some platform-specific code in all the
> > sanitizers, and many of them heavily depend
> > on the address space layout. Porting TSan and MSan to 32-bit address
> space
> > is especially hard, and we don't plan
> > to do this anytime soon. I think it makes sense to build only the
> libraries
> > that are expected to work on a given arch.
> >
> I should have made clear this is very much a WIP. I expect to have make
> an effort to port compiler-rt, but first I need to be able to generate
> elf32_x86_64 objects with Clang.  I confess, my method of porting code
> to x32 so far has consisted of trying to build existing code and
> modifying what breaks, or disabling features where inapplicable.  I
> haven't studied the code well enough to understand and predict where I'm
> going to have make modification in advance.  It's worked so far with
> most things I've attempted but LLVM/Clang/compiler-rt is an order of
> magnitude more complex than anything else I've poked at.  The biggest
> success I've had so far with this method is porting of Mozilla
> Spidermonkey/js17.
>

So, IIUC, if you're working on making LLVM/Clang/compiler-rt source tree
build on x32 host, I suggest your first step should be: disable building
compiler-rt
on x32 host :) One of the reasons: in makefile-based build compiler-rt
sources
are compiled with just-built Clang (I honestly don't know if Clang can
target x32
at the moment). Another reason: compiler-rt code is really arch-specific,
and even
if it compiles, it wouldn't work.


>
> > 2) If we're stepping on the path of porting some sanitizers to x32, it
> > would be great to
> > setup a buildbot, make our tests pass cleanly, and make this bot public
> to
> > catch regressions.
> > Do you have plans for that? Running sanitizer test suites also leads us
> > to...
> >
> I'm new to llvm/clang, I'm going to have to take guidance from others.
>
> > 3) Do you plan to add support for building sanitizers on x32 to CMake
> build
> > system? It would
> > make sense (and, in fact, I would start from there), as our testsuite can
> > be run only in CMake builds.
> >
> I can do so, (locally switch to cmake) I have a little experience with
> cmake so I should be able to figure it out.  From my distro point of
> view, the plan on Gentoo is to switch to CMake for the LLVM/Clang
> ebuild, but it hasn't happened yet.  Perhaps this could be expedited, I
> can contact the package maintainer.


FTR, CMake would probably see that we our host is neither x86_64 nor i386,
and won't build anything in compiler-rt. If it wouldn't, we should go and
fix this.

-- 
Alexey Samsonov, MSK
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