gcc3_linux_{aarch64,x86-64} need the __cxa_exception hack in deleteException

* gcc3_linux_aarch64 needs a hack to detect the reserve member in LLVM >= 10
  libcxxabi __cxa_exception, in addition to the existing hack for LLVM 5.

  On macOS arm64 (which shares the bridges/source/cpp_uno/gcc3_linux_aarch64/
  code) we know that we always target a >= LLVM 10 libcxxabi, so we do not need
  neither of the two hacks there.

  (And a7d1fed24557b203acb5016a98af26f4ef24d27a "Hack to dynamically adapt to
  __cxa_exceptiom in LLVM 5.0 libcxxabi" had introduced a "fillUnoException" vs.
  "mapException" typo in the comment when it copied it from
  bridges/source/cpp_uno/gcc3_macosx_x86-64/except.cxx.)

* Similarly, gcc3_linux_x86_64 needs both hacks when it is built against
  libcxxabi (and the need for the LLVM 5 hack had gone unnoticed there for now).

* It is not clear to me now why gcc3_macosx_x86-64 needs the LLVM 5 hack (which
  I even initially developed for that platform,
  7a9dd3d482deeeb3ed1d50074e56adbd3f928296 "Hack to dynamically adapt to
  __cxa_exceptiom in LLVM 5.0 libcxxabi") but not the LLVM >= 10 hack (although
  it does need the corresponding hack in fillUnoException when running against
  recent upstream LLVM trunk libcxxabi, f4b6f6a8ae60bdec53512728d00853b73fa18500
  "Hack to dynamically adapt to __cxa_exceptiom in LLVM 11 libcxxabi".

Change-Id: I8e7a5c871fbeeaf82bbd16fa03e73f10f229da93
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/100656
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

2 files changed, 88 insertions, 8 deletions

diff --git a/bridges/source/cpp_uno/gcc3_linux_aarch64/abi.cxx b/bridges/source/cpp_uno/gcc3_linux_aarch64/abi.cxx
index 492c14898977..988502713639 100644
--- a/bridges/source/cpp_uno/gcc3_linux_aarch64/abi.cxx
+++ b/bridges/source/cpp_uno/gcc3_linux_aarch64/abi.cxx
@@ -162,8 +162,8 @@ std::type_info * getRtti(typelib_TypeDescription const & type) {
 extern "C" void _GLIBCXX_CDTOR_CALLABI deleteException(void * exception) {
     __cxxabiv1::__cxa_exception * header =
         static_cast<__cxxabiv1::__cxa_exception *>(exception) - 1;
-#if defined _LIBCPPABI_VERSION // detect libc++abi
-    // The libcxxabi commit
+#if !defined MACOSX && defined _LIBCPPABI_VERSION // detect libc++abi
+    // First, the libcxxabi commit
     // <http://llvm.org/viewvc/llvm-project?view=revision&revision=303175>
     // "[libcxxabi] Align unwindHeader on a double-word boundary" towards
     // LLVM 5.0 changed the size of __cxa_exception by adding
@@ -173,21 +173,48 @@ extern "C" void _GLIBCXX_CDTOR_CALLABI deleteException(void * exception) {
     // to the final member unwindHeader, on x86-64 effectively adding a hole of
     // size 8 in front of that member (changing its offset from 88 to 96,
     // sizeof(__cxa_exception) from 120 to 128, and alignof(__cxa_exception)
-    // from 8 to 16); a hack to dynamically determine whether we run against a
+    // from 8 to 16); the "header1" hack below to dynamically determine whether we run against a
     // LLVM 5 libcxxabi is to look at the exceptionDestructor member, which must
-    // point to this function (the use of __cxa_exception in fillUnoException is
+    // point to this function (the use of __cxa_exception in mapException is
     // unaffected, as it only accesses members towards the start of the struct,
     // through a pointer known to actually point at the start).  The libcxxabi commit
     // <https://github.com/llvm/llvm-project/commit/9ef1daa46edb80c47d0486148c0afc4e0d83ddcf>
     // "Insert padding before the __cxa_exception header to ensure the thrown" in LLVM 6
-    // removes the need for this hack, so it can be removed again once we can be sure that we only
-    // run against libcxxabi from LLVM >= 6:
+    // removes the need for this hack, so the "header1" hack can be removed again once we can be
+    // sure that we only run against libcxxabi from LLVM >= 6.
+    //
+    // Second, the libcxxabi commit
+    // <https://github.com/llvm/llvm-project/commit/674ec1eb16678b8addc02a4b0534ab383d22fa77>
+    // "[libcxxabi] Insert padding in __cxa_exception struct for compatibility" in LLVM 10 changed
+    // the layout of the start of __cxa_exception to
+    //
+    //  [8 byte  void *reserve]
+    //   8 byte  size_t referenceCount
+    //
+    // so the "header2" hack below to dynamically determine whether we run against a LLVM >= 10
+    // libcxxabi is to look whether the exceptionDestructor (with its known value) has increased its
+    // offset by 8.  As described in the definition of __cxa_exception
+    // (bridges/source/cpp_uno/gcc3_linux_aarch64/abi.hxx), the "header2" hack (together with the
+    // "#ifdef MACOSX" in the definition of __cxa_exception and the corresponding hack in call in
+    // bridges/source/cpp_uno/gcc3_linux_aarch64/uno2cpp.cxx) can be dropped once we can be sure
+    // that we only run against new libcxxabi that has the reserve member.
     if (header->exceptionDestructor != &deleteException) {
-        header = reinterpret_cast<__cxxabiv1::__cxa_exception *>(
+        auto const header1 = reinterpret_cast<__cxxabiv1::__cxa_exception *>(
             reinterpret_cast<char *>(header) - 8);
-        assert(header->exceptionDestructor == &deleteException);
+        if (header1->exceptionDestructor == &deleteException) {
+            header = header1;
+        } else {
+            auto const header2 = reinterpret_cast<__cxxabiv1::__cxa_exception *>(
+                reinterpret_cast<char *>(header) + 8);
+            if (header2->exceptionDestructor == &deleteException) {
+                header = header2;
+            } else {
+                assert(false);
+            }
+        }
     }
 #endif
+    assert(header->exceptionDestructor == &deleteException);
     OUString unoName(toUnoName(header->exceptionType->name()));
     typelib_TypeDescription * td = 0;
     typelib_typedescription_getByName(&td, unoName.pData);
diff --git a/bridges/source/cpp_uno/gcc3_linux_x86-64/except.cxx b/bridges/source/cpp_uno/gcc3_linux_x86-64/except.cxx
index 981ddfe676f7..2a92dba37475 100644
--- a/bridges/source/cpp_uno/gcc3_linux_x86-64/except.cxx
+++ b/bridges/source/cpp_uno/gcc3_linux_x86-64/except.cxx
@@ -82,6 +82,59 @@ extern "C" {
 static void _GLIBCXX_CDTOR_CALLABI deleteException( void * pExc )
 {
     __cxxabiv1::__cxa_exception const * header = static_cast<__cxxabiv1::__cxa_exception const *>(pExc) - 1;
+#if defined _LIBCPPABI_VERSION // detect libc++abi
+    // First, the libcxxabi commit
+    // <http://llvm.org/viewvc/llvm-project?view=revision&revision=303175>
+    // "[libcxxabi] Align unwindHeader on a double-word boundary" towards
+    // LLVM 5.0 changed the size of __cxa_exception by adding
+    //
+    //   __attribute__((aligned))
+    //
+    // to the final member unwindHeader, on x86-64 effectively adding a hole of
+    // size 8 in front of that member (changing its offset from 88 to 96,
+    // sizeof(__cxa_exception) from 120 to 128, and alignof(__cxa_exception)
+    // from 8 to 16); the "header1" hack below to dynamically determine whether we run against a
+    // LLVM 5 libcxxabi is to look at the exceptionDestructor member, which must
+    // point to this function (the use of __cxa_exception in fillUnoException is
+    // unaffected, as it only accesses members towards the start of the struct,
+    // through a pointer known to actually point at the start).  The libcxxabi commit
+    // <https://github.com/llvm/llvm-project/commit/9ef1daa46edb80c47d0486148c0afc4e0d83ddcf>
+    // "Insert padding before the __cxa_exception header to ensure the thrown" in LLVM 6
+    // removes the need for this hack, so the "header1" hack can be removed again once we can be
+    // sure that we only run against libcxxabi from LLVM >= 6.
+    //
+    // Second, the libcxxabi commit
+    // <https://github.com/llvm/llvm-project/commit/674ec1eb16678b8addc02a4b0534ab383d22fa77>
+    // "[libcxxabi] Insert padding in __cxa_exception struct for compatibility" in LLVM 10 changed
+    // the layout of the start of __cxa_exception to
+    //
+    //  [8 byte  void *reserve]
+    //   8 byte  size_t referenceCount
+    //
+    // so the "header2" hack below to dynamically determine whether we run against a LLVM >= 10
+    // libcxxabi is to look whether the exceptionDestructor (with its known value) has increased its
+    // offset by 8.  As described in the definition of __cxa_exception
+    // (bridges/source/cpp_uno/gcc3_linux_x86-64/share.hxx), the "header2" hack (together with the
+    // "#if 0" in the definition of __cxa_exception and the corresponding hack in fillUnoException)
+    // can be dropped once we can be sure that we only run against new libcxxabi that has the
+    // reserve member.
+    if (header->exceptionDestructor != &deleteException) {
+        auto const header1 = reinterpret_cast<__cxa_exception const *>(
+            reinterpret_cast<char const *>(header) - 8);
+        if (header1->exceptionDestructor == &deleteException) {
+            header = header1;
+        } else {
+            auto const header2 = reinterpret_cast<__cxa_exception const *>(
+                reinterpret_cast<char const *>(header) + 8);
+            if (header2->exceptionDestructor == &deleteException) {
+                header = header2;
+            } else {
+                assert(false);
+            }
+        }
+    }
+#endif
+    assert(header->exceptionDestructor == &deleteException);
     typelib_TypeDescription * pTD = nullptr;
     OUString unoName( toUNOname( header->exceptionType->name() ) );
     ::typelib_typedescription_getByName( &pTD, unoName.pData );