diff options
author | Stephan Bergmann <sbergman@redhat.com> | 2023-01-04 12:14:22 +0100 |
---|---|---|
committer | Stephan Bergmann <sbergman@redhat.com> | 2023-01-04 13:49:58 +0000 |
commit | ef533553559fe09b4afab651fc692885d1acf4ed (patch) | |
tree | bbd17cba9c5253ddbe62250efa63c3d169156180 /bridges/source/cpp_uno/gcc3_solaris_sparc/cpp2uno.cxx | |
parent | 146eb1aa750a7612deb9d3e1825a7a2e1256bd4d (diff) |
Rudimentary support for dynamic_cast on UNO proxy objects
<https://gerrit.libreoffice.org/c/core/+/144139> "New loplugin:unocast" had
argued that uses of dynamic_cast from a UNO interface type are broken in general
(because if the source object is a proxy from the C*+ UNO bridge, its vtable's
RTTI slot will normally not be set up, which can cause a crash), and should be
replaced with uses of XUnoTunnel. Which the various recent "loplugin:unocast
(...)" commits started to do. However, it became clear that that is not the
most ideal way forward: For one, getting more and more implementations of
XUnoTunnel::getSomething into existing class hierarchies is error prone, as each
such implementation must manually delegate to all its base class
implementations. For another, uses of comphelper::getFromUnoTunnel (which often
needs to do a queryInterface to XUnoTunnel first) are easily more expensive than
uses of dynamic_cast.
Thanks to Noel, the insight here is that for the use case of a dynamic_cast from
a UNO interface type to a local C++ class type, and if the source object is a
proxy, it is sufficient that the dynamic_cast will not crash. It will
necessarily always return null (as the proxy will never be the implementation of
a local C++ class type), so it is sufficient to fill the RTTI slots of the
proxies' vtables with dummy values. That avoids having to set up proper RTTI
for those potentially multiple-inheritance proxy types. (And with this in
place, all those recent "loplugin:unocast (...)" commits can be reverted again
in a next step.)
I verified the changes for the gcc3_linux_aarch64 (on macOS), gcc3_linux_intel,
gcc3_linux_x86-64, gcc3_macosx_x86-64, msvc_win32_intel, and msvc_win32_x86-64
bridges. The changes for all the other bridges were done blindly.
(For gcc3_linux_x86-64, which already conditionally supported proper RTTI for
UBSan, setting the offset-to-top slot to non-zero had to be made conditional
too, as the dummy ProxyRtti will always pretend to be a full class rather than a
potential base class that could have a non-zero offset-to-top value. For
msvc_win32_*, it turned out that the existing code to set up dummy XInterface
RTTI (which was there for reasons lost to history) was broken.)
Change-Id: Iec4b8067d26b14b6fb02c2fdd15e1eee20919590
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/145038
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>
Diffstat (limited to 'bridges/source/cpp_uno/gcc3_solaris_sparc/cpp2uno.cxx')
-rw-r--r-- | bridges/source/cpp_uno/gcc3_solaris_sparc/cpp2uno.cxx | 14 |
1 files changed, 12 insertions, 2 deletions
diff --git a/bridges/source/cpp_uno/gcc3_solaris_sparc/cpp2uno.cxx b/bridges/source/cpp_uno/gcc3_solaris_sparc/cpp2uno.cxx index 639b8da3dc88..55c1360f844e 100644 --- a/bridges/source/cpp_uno/gcc3_solaris_sparc/cpp2uno.cxx +++ b/bridges/source/cpp_uno/gcc3_solaris_sparc/cpp2uno.cxx @@ -17,6 +17,10 @@ * the License at http://www.apache.org/licenses/LICENSE-2.0 . */ +#include <sal/config.h> + +#include <typeinfo> + #include <com/sun/star/uno/genfunc.hxx> #include <sal/log.hxx> #include <typelib/typedescription.hxx> @@ -475,7 +479,7 @@ unsigned char * codeSnippet( } //end of namespace -struct bridges::cpp_uno::shared::VtableFactory::Slot { void * fn; }; +struct bridges::cpp_uno::shared::VtableFactory::Slot { void const * fn; }; bridges::cpp_uno::shared::VtableFactory::Slot * bridges::cpp_uno::shared::VtableFactory::mapBlockToVtable(void * block) @@ -489,6 +493,12 @@ std::size_t bridges::cpp_uno::shared::VtableFactory::getBlockSize( return (slotCount + 2) * sizeof (Slot) + slotCount * codeSnippetSize; } +namespace { +// Some dummy type whose RTTI is used in the synthesized proxy vtables to make uses of dynamic_cast +// on such proxy objects not crash: +struct ProxyRtti {}; +} + bridges::cpp_uno::shared::VtableFactory::Slot * bridges::cpp_uno::shared::VtableFactory::initializeBlock( void * block, sal_Int32 slotCount, sal_Int32, @@ -496,7 +506,7 @@ bridges::cpp_uno::shared::VtableFactory::initializeBlock( { Slot * slots = mapBlockToVtable(block); slots[-2].fn = 0; //null - slots[-1].fn = 0; //destructor + slots[-1].fn = &typeid(ProxyRtti); return slots + slotCount; } |