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

[Alexey Samsonov]

On Thu, Aug 22, 2013 at 11:56 AM, Steven Newbury <steve at snewbury.org.uk>wrote:

> On Thu, 2013-08-22 at 11:50 +0400, Alexey Samsonov wrote:
> > 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.
> >
> See accompanied Clang patch in other email.  I've attempted to get Clang
> to target x32, I'm also suspicious that x32 built clang isn't correctly
> working to produce 64-bit code, but that's a somewhat different bug that
> I haven't yet attempted to address.  Without modifying Clang to target
> x32, the x32 *built* Clang fails to compile compiler-rt with -m64, I
> need help decoding the crash backtrace to figure out where that bug
> lies, but it's not related to (or helped by) my patch.
>

So, it looks like Clang built on x32 host:
(a) doesn't work with -m64 (can't target x86_64)
(b) can target x32 with your patch.
If that's the case, (a) should be investigated (maybe, you can open a bug
for this
as a start), while you should try to get your patch for (b) submitted.
Let's move the
discussion to that thread, most likely you'll have to add tests and find a
reviewer for that patch.


> >
> > >
> > > > 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.
> >
>
> Maybe.  Although, technically it *is* x86_64, but with a different ABI.
> I don't know how that's handled, although it works for ARM/MIPS, right??
>

Yes, we're able to target ARM on x86_64 host if that's what you're asking
about.

-- 
Alexey Samsonov, MSK
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20130822/6d0d803a/attachment.html>