[Bug 263370] devel/libunwind: unwind.h incompatible with base unwind.h

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=263370

            Bug ID: 263370
           Summary: devel/libunwind: unwind.h incompatible with base
                    unwind.h
           Product: Ports & Packages
           Version: Latest
          Hardware: Any
                OS: Any
            Status: New
          Severity: Affects Only Me
          Priority: ---
         Component: Individual Port(s)
          Assignee: sunpoet@FreeBSD.org
          Reporter: tijl@FreeBSD.org
                CC: brooks@FreeBSD.org, dim@FreeBSD.org,
                    emaste@freebsd.org, jhb@FreeBSD.org,
                    pkubaj@FreeBSD.org, re@FreeBSD.org
            Blocks: 262008
             Flags: maintainer-feedback?(sunpoet@FreeBSD.org)
                CC:
          Assignee: sunpoet@FreeBSD.org

The base system unwind.h (since base c00d34566536) aligns struct
_Unwind_Exception using __attribute__((__aligned__)) which is 16 byte alignment
on i386 and amd64.  The unwind.h from devel/libunwind used to have this as well
but replaced it (erroneously) with _Alignas(8) in version 1.6 which is
incompatible.  This difference affects the layout (size, alignment, padding,
field offsets) of struct __cxa_exception in cxxabi.h.

By default libreoffice depends on gstreamer which by default depends on
devel/libunwind, so with default options libreoffice is built with the wrong
_Unwind_Exception and __cxa_exception.  This leads to crashes already during
build, at least on i386 (gengal.bin segfaults as reported in bug 262008).  For
amd64, libreoffice has hacks in place to detect ABI differences at runtime
which also happen to work in this case.  I suspect the same happens with
openoffice.

Either devel/libunwind needs a patch that reverts
https://github.com/libunwind/libunwind/commit/da8dc856ab5646e04160060aae9425db3f5428ce#diff-0b26e6872c56fde17faa6297bdcd1cc72357de35a30894de5d48b4006e5fe83a=
but how does that affect older versions of FreeBSD?  Or it could be configured
with --disable-unwind-header so its unwind.h isn't installed, but then how does
that affect other ports?

Additionally, the comments in struct __cxa_exception in cxxabi.h state that
_Unwind_Exception is 64-bit aligned and that adding referenceCount at the
beginning is safe.  This may have been true at the time because LLVM libunwind
added __attribute__((__aligned__)) later (to be GCC compatible I think:
https://github.com/llvm/llvm-project/commit/19f802ff68361af0a28c8ad6e12daf9bd740b96d),
but it's not safe now and the GCC folks were bitten by this as well
(https://gcc.gnu.org/bugzilla/show_bug.cgi?id=38732).  For architectures where
__attribute__((__aligned__)) means 16 byte alignment adding it to
_Unwind_Exception also adds 8 bytes of padding right before the unwindHeader
field in __cxa_exception which breaks ABI.  That's why libreoffice on amd64 has
the hacks I mentioned above.  Could we change our libcxxrt similar to what
libc++abi did in
https://github.com/llvm/llvm-project/commit/f2a436058fcbc11291e73badb44e243f61046183?
 I believe that way we maintain ABI compatibility at least on 64-bit
architectures, i.e. libreoffice built with FreeBSD 13.0 cxxabi.h and unwind.h
(or devel/libunwind unwind.h with _Alignas(8)) would then run on FreeBSD 13.1. 
Can we delay FreeBSD 13.1 release until this is fully understood and sorted
out?


Referenced Bugs:

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=262008
[Bug 262008] editors/libreoffice failed to build
-- 
You are receiving this mail because:
You are the assignee for the bug.