Add downstream libunwind changes from emscripten (#2)

Author: aheejin

libunwind/include/unwind_itanium.h

@@ -24,7 +24,7 @@ struct _Unwind_Exception {
                             _Unwind_Exception *exc);
 #if defined(__SEH__) && !defined(__USING_SJLJ_EXCEPTIONS__)
   uintptr_t private_[6];
-#else
+#elif !defined(__USING_WASM_EXCEPTIONS__)
   uintptr_t private_1; // non-zero means forced unwind
   uintptr_t private_2; // holds sp that phase1 found for phase2 to use
 #endif

libunwind/src/Unwind-wasm.c

@@ -0,0 +1,110 @@
+#include "config.h"
+#include "unwind.h"
+#include <stdbool.h>
+#include <threads.h>
+
+#ifdef __USING_WASM_EXCEPTIONS__
+
+_Unwind_Reason_Code __gxx_personality_wasm0(int version, _Unwind_Action actions,
+                                            uint64_t exceptionClass,
+                                            _Unwind_Exception *unwind_exception,
+                                            _Unwind_Context *context);
+
+struct _Unwind_LandingPadContext {
+  // Input information to personality function
+  uintptr_t lpad_index; // landing pad index
+  uintptr_t lsda;       // LSDA address
+
+  // Output information computed by personality function
+  uintptr_t selector; // selector value
+};
+
+// Communication channel between compiler-generated user code and personality
+// function
+thread_local struct _Unwind_LandingPadContext __wasm_lpad_context;
+
+/// Calls to this function is in landing pads in compiler-generated user code.
+/// In other EH schemes, stack unwinding is done by libunwind library, which
+/// calls the personality function for each each frame it lands. On the other
+/// hand, WebAssembly stack unwinding process is performed by a VM, and the
+/// personality function cannot be called from there. So the compiler inserts
+/// a call to this function in landing pads in the user code, which in turn
+/// calls the personality function.
+_Unwind_Reason_Code _Unwind_CallPersonality(void *exception_ptr) {
+  struct _Unwind_Exception *exception_object =
+      (struct _Unwind_Exception *)exception_ptr;
+  _LIBUNWIND_TRACE_API("_Unwind_CallPersonality(exception_object=%p)",
+                       (void *)exception_object);
+
+  // Reset the selector.
+  __wasm_lpad_context.selector = 0;
+
+  // Call personality function. Wasm does not have two-phase unwinding, so we
+  // only do the cleanup phase.
+  _Unwind_Reason_Code ret = __gxx_personality_wasm0(
+      1, _UA_SEARCH_PHASE, exception_object->exception_class, exception_object,
+      (struct _Unwind_Context *)&__wasm_lpad_context);
+  return ret;
+}
+
+/// Called by __cxa_throw.
+_LIBUNWIND_EXPORT _Unwind_Reason_Code
+_Unwind_RaiseException(_Unwind_Exception *exception_object) {
+  _LIBUNWIND_TRACE_API("_Unwind_RaiseException(exception_object=%p)",
+                       (void *)exception_object);
+  __builtin_wasm_throw(0, exception_object);
+}
+
+/// Called by __cxa_end_catch.
+_LIBUNWIND_EXPORT void
+_Unwind_DeleteException(_Unwind_Exception *exception_object) {
+  _LIBUNWIND_TRACE_API("_Unwind_DeleteException(ex_obj=%p)",
+                       (void *)(exception_object));
+  if (exception_object->exception_cleanup != NULL)
+    (*exception_object->exception_cleanup)(_URC_FOREIGN_EXCEPTION_CAUGHT,
+                                           exception_object);
+}
+
+/// Called by personality handler to alter register values.
+_LIBUNWIND_EXPORT void _Unwind_SetGR(struct _Unwind_Context *context, int index,
+                                     uintptr_t value) {
+  _LIBUNWIND_TRACE_API("_Unwind_SetGR(context=%p, index=%d, value=%lu)",
+                       (void *)context, index, value);
+  // We only use this function to set __wasm_lpad_context.selector field, which
+  // is index 1 in the personality function.
+  if (index != 1)
+    return;
+  ((struct _Unwind_LandingPadContext *)context)->selector = value;
+}
+
+/// Called by personality handler to get instruction pointer.
+_LIBUNWIND_EXPORT uintptr_t _Unwind_GetIP(struct _Unwind_Context *context) {
+  // The result will be used as an 1-based index after decrementing 1, so we
+  // increment 2 here
+  uintptr_t result =
+      ((struct _Unwind_LandingPadContext *)context)->lpad_index + 2;
+  _LIBUNWIND_TRACE_API("_Unwind_GetIP(context=%p) => %lu", (void *)context,
+                       result);
+  return result;
+}
+
+/// Not used in wasm.
+_LIBUNWIND_EXPORT void _Unwind_SetIP(struct _Unwind_Context *context,
+                                     uintptr_t value) {}
+
+/// Called by personality handler to get LSDA for current frame.
+_LIBUNWIND_EXPORT uintptr_t
+_Unwind_GetLanguageSpecificData(struct _Unwind_Context *context) {
+  uintptr_t result = ((struct _Unwind_LandingPadContext *)context)->lsda;
+  _LIBUNWIND_TRACE_API("_Unwind_GetLanguageSpecificData(context=%p) => 0x%lx",
+                       (void *)context, result);
+  return result;
+}
+
+/// Not used in wasm.
+_LIBUNWIND_EXPORT uintptr_t
+_Unwind_GetRegionStart(struct _Unwind_Context *context) {
+  return 0;
+}
+
+#endif

libunwind/src/config.h

@@ -98,6 +98,7 @@
                                              SYMBOL_NAME(name)))               \
   extern "C" _LIBUNWIND_EXPORT __typeof(name) aliasname;
 #endif
+#elif defined(__EMSCRIPTEN__)
 #else
 #error Unsupported target
 #endif