[cfe-dev] [libcxxabi] Contributing ARM EHABI support for libcxxabi

[Nico Weber]

On Tue, Dec 3, 2013 at 3:45 PM, Nick Kledzik <kledzik at apple.com> wrote:

>
> On Dec 3, 2013, at 2:32 PM, Nico Weber <thakis at chromium.org> wrote:
>
> > Hi,
> >
> > We’re evaluating using libc++ and libc++abi for Chromium/Android. While
> libc++abi has an unwind implementation since r192136, we noticed that
> there’s no support for unwinding using ARM EHABI-style unwind information,
> so in the last two weeks some of us (Albert Wong, Antoine Labour, Dana
> Jansens, and I) prototyped support for it, and we’re able to catch at least
> simple exceptions (you can look at our code here [1]). We believe at least
> some of our code is ready for upstreaming.
> >
> > A few questions:
> > 1.) Is there interest for this upstream?
> > 2.) Who should review this? Howard? Nick? Anton?
> I can.
>
> > 3.) r192136 didn’t add any test – how should testing of unwinding code
> work? Is running the exception tests in the libc++ suite enough?
> The Darwin libunwind project (
> http://opensource.apple.com/source/libunwind/libunwind-35.3/) on which
> this was based had some a small test suite, but it did not fit into the
> existing libcxxabi test suite which assumes target==host and every test is
> one .cpp file.
>

Ok. I tried running at least the libc++abi test suite to make sure we don't
completely break exception handling on darwin, but it looks like the
buildit script doesn't build libunwind, and if I try to get it to compile
(attached), the compiler complains about mach-o/dyld_priv.h – is it
currently possible to run libc++abi tests for the Unwind bits of libc++abi
on darwin?


>
> > 4.) The unwind code doesn’t adhere to llvm style all that much – does it
> make sense to clang-format while it still has next to no svn history before
> landing other changes?
> The Unwind part conforms to llvm style much more than the rest of
> libcxxabi does ;-)  I ran clang-format on the Unwind sources at one point
> during the port from darwin.   Feel free to use clang-format on new code.
>  My personal grip with clang-format is that it throws away all vertical
> alignment.
>
>
> -Nick
>
>
>
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Index: lib/buildit
===================================================================
--- lib/buildit	(revision 196341)
+++ lib/buildit	(working copy)
@@ -97,3 +97,24 @@
 then
     rm *.o
 fi
+
+# libunwind is a separate library on Darwin.
+case $TRIPLE in
+  *-apple-*)
+    for FILE in ../src/Unwind/*.c*; do
+            $CXX -c -g -O3 $RC_CFLAGS $EXTRA_FLAGS -I../include $OPTIONS $FILE
+    done
+    LDSHARED_FLAGS="-o libunwind.dylib \
+        -dynamiclib -nodefaultlibs  \
+        -current_version ${RC_ProjectSourceVersion} \
+        -compatibility_version 1 \
+        -install_name /usr/lib/system/libunwind.dylib \
+        "  # FIXME: link to libsystem_malloc.dylib and friends?
+    $CC *.o $RC_CFLAGS $LDSHARED_FLAGS $EXTRA_FLAGS
+
+    if [ -z $RC_XBS ]
+    then
+        rm *.o
+    fi
+    ;;
+esac