[libunwind] [SEH] Sync LSDA and handler between unw_proc_info_t and DISPATCHER_CONTEXT

[mstorsjo]

Summary

For normal C++ unwinding, we get _dispContext initialized by the
prepopulated DISPATCHER_CONTEXT in _GCC_specific_handler, which
we set with __unw_seh_set_disp_ctx.

When doing force unwinding, we step and populate the unw_proc_info_t
struct _info with getInfoFromSEH, but when we execute the handler
via the __libunwind_seh_personality wrapper function, we execute
the handler set in DISPATCHER_CONTEXT.

Whenever updating these fields in either _info or _dispContext,
sync them to the other one too.

This fixes one aspect of the libcxxabi force_unwind*.pass.cpp tests on
x86_64.

[cdavis5x]

How did I not catch this?? I could've sworn the tests all passed when I originally put this in...

[mstorsjo]

In D147637#4249744, @cdavis5x wrote:

How did I not catch this?? I could've sworn the tests all passed when I originally put this in...

FWIW, libunwind's tests don't really exercise the forced unwinding much, but libcxxabi has got much more tests for that.

[phosek]

LGTM

libunwind/src/UnwindCursor.hpp

public:
   virtual bool        getFunctionName(char *buf, size_t len, unw_word_t *off);
   virtual void        setInfoBasedOnIPRegister(bool isReturnAddress = false);
   virtual const char *getRegisterName(int num);
 #ifdef __arm__
   virtual void        saveVFPAsX();
 #endif
 
   DISPATCHER_CONTEXT *getDispatcherContext() { return &_dispContext; }
-  void setDispatcherContext(DISPATCHER_CONTEXT *disp) { _dispContext = *disp; }
+  void setDispatcherContext(DISPATCHER_CONTEXT *disp) {
+    _dispContext = *disp;
+    _info.lsda = reinterpret_cast<unw_word_t>(_dispContext.HandlerData);
+    if (_dispContext.LanguageHandler) {
+      _info.handler = reinterpret_cast<unw_word_t>(__libunwind_seh_personality);
+    } else
+      _info.handler = 0;
+  }
 
   // libunwind does not and should not depend on C++ library which means that we
   // need our own definition of inline placement new.
   static void *operator new(size_t, UnwindCursor<A, R> *p) { return p; }
 
 private:
 
   pint_t getLastPC() const { return _dispContext.ControlPc; }
if (pc != getLastPC()) {
     if (xdata->Flags & (UNW_FLAG_EHANDLER|UNW_FLAG_UHANDLER)) {
       // The personality is given in the UNWIND_INFO itself. The LSDA immediately
       // follows the UNWIND_INFO. (This follows how both Clang and MSVC emit
       // these structures.)
       // N.B. UNWIND_INFO structs are DWORD-aligned.
       uint32_t lastcode = (xdata->CountOfCodes + 1) & ~1;
       const uint32_t *handler = reinterpret_cast<uint32_t *>(&xdata->UnwindCodes[lastcode]);
       _info.lsda = reinterpret_cast<unw_word_t>(handler+1);
+      _dispContext.HandlerData = reinterpret_cast<void *>(_info.lsda);
+      _dispContext.LanguageHandler =
+          reinterpret_cast<EXCEPTION_ROUTINE *>(base + *handler);
       if (*handler) {
         _info.handler = reinterpret_cast<unw_word_t>(__libunwind_seh_personality);
       } else
         _info.handler = 0;
     } else {
       _info.lsda = 0;
       _info.handler = 0;
     }