From 183fe986d0a937ac9cab3ba25732f23b3f9cefe6 Mon Sep 17 00:00:00 2001
From: Jan Kotas <jkotas@microsoft.com>
Date: Tue, 6 Jun 2023 19:20:00 -0700
Subject: [PATCH] WIP

---
 .../llvm-libunwind/src/EHHeaderParser.hpp     | 64 +++++++++++++++++++
 .../llvm-libunwind/src/UnwindCursor.hpp       | 21 ++++++
 2 files changed, 85 insertions(+)

diff --git a/src/native/external/llvm-libunwind/src/EHHeaderParser.hpp b/src/native/external/llvm-libunwind/src/EHHeaderParser.hpp
index ed4317c89055c9..69ffe7036d948c 100644
--- a/src/native/external/llvm-libunwind/src/EHHeaderParser.hpp
+++ b/src/native/external/llvm-libunwind/src/EHHeaderParser.hpp
@@ -112,6 +112,67 @@ bool EHHeaderParser<A>::findFDE(A &addressSpace, pint_t pc, pint_t ehHdrStart,
 
   if (hdrInfo.fde_count == 0) return false;
 
+  pint_t tableEntryDebug = 0;
+
+  // Special-case the most common encoding with faster binary search implementation
+  if (hdrInfo.table_enc == (DW_EH_PE_sdata4 | DW_EH_PE_datarel))
+  {
+    size_t tableEntrySize = 8;
+
+    pint_t relpc = pc - ehHdrStart;
+
+    size_t low = 0;
+    size_t high = hdrInfo.fde_count - 1;
+
+    // Binary search the entry table
+    // Use linear search once we get down to a small number of elements
+    // to avoid binary search overhead.
+    while (high - low > 10) {
+      size_t middle = low + (high - low) / 2;
+
+      pint_t tableEntry = hdrInfo.table + middle * tableEntrySize;
+      pint_t relstart = (pint_t)(int32_t)addressSpace.get32(tableEntry);
+
+      if (relpc < relstart) {
+        high = middle - 1;
+      } else {
+        low = middle;
+      }
+    }
+
+    for (size_t i = low; i < high; i++) {
+      pint_t tableEntry = hdrInfo.table + (i + 1) * tableEntrySize;
+      pint_t relstart = (pint_t)(int32_t)addressSpace.get32(tableEntry);
+
+      if (relpc < relstart) {
+        high = i;
+        break;
+      }
+    }
+
+    pint_t tableEntry = hdrInfo.table + high * tableEntrySize;
+
+    // Have to decode the whole FDE for the PC range anyway, so just throw away
+    // the PC start.
+    pint_t fde =
+        (pint_t)(int32_t)addressSpace.get32(tableEntry + 4) + ehHdrStart;
+    const char *message =
+        CFI_Parser<A>::decodeFDE(addressSpace, fde, fdeInfo, cieInfo);
+    if (message != NULL) {
+      _LIBUNWIND_DEBUG_LOG("EHHeaderParser::decodeTableEntry: bad fde: %s",
+                           message);
+      return false;
+    }
+
+#if defined(NDEBUG)
+    if (pc >= fdeInfo->pcStart && pc < fdeInfo->pcEnd)
+        return true;
+    return false;
+#else
+    tableEntryDebug = tableEntry;
+#endif
+  }
+
   size_t tableEntrySize = getTableEntrySize(hdrInfo.table_enc);
   pint_t tableEntry;
 
@@ -134,6 +195,9 @@ bool EHHeaderParser<A>::findFDE(A &addressSpace, pint_t pc, pint_t ehHdrStart,
   }
 
   tableEntry = hdrInfo.table + low * tableEntrySize;
+
+  assert(tableEntry == tableEntryDebug);
+
   if (decodeTableEntry(addressSpace, tableEntry, ehHdrStart, ehHdrEnd,
                        hdrInfo.table_enc, fdeInfo, cieInfo)) {
     if (pc >= fdeInfo->pcStart && pc < fdeInfo->pcEnd)
diff --git a/src/native/external/llvm-libunwind/src/UnwindCursor.hpp b/src/native/external/llvm-libunwind/src/UnwindCursor.hpp
index b57134cdd19bb9..12b9ca2a9154b0 100644
--- a/src/native/external/llvm-libunwind/src/UnwindCursor.hpp
+++ b/src/native/external/llvm-libunwind/src/UnwindCursor.hpp
@@ -124,6 +124,25 @@ class _LIBUNWIND_HIDDEN DwarfFDECache {
   static entry _initialBuffer[64];
 };
 
+template <typename A>
+typename A::pint_t DwarfFDECache<A>::findFDE(pint_t mh, pint_t pc) {
+    return 0;
+}
+
+template <typename A>
+void DwarfFDECache<A>::add(pint_t mh, pint_t ip_start, pint_t ip_end,
+                           pint_t fde) {
+}
+
+template <typename A> void DwarfFDECache<A>::removeAllIn(pint_t mh) {
+}
+
+template <typename A>
+void DwarfFDECache<A>::iterateCacheEntries(void (*func)(
+    unw_word_t ip_start, unw_word_t ip_end, unw_word_t fde, unw_word_t mh)) {
+}
+
+#if 0
 template <typename A>
 typename DwarfFDECache<A>::entry *
 DwarfFDECache<A>::_buffer = _initialBuffer;
@@ -226,6 +245,8 @@ void DwarfFDECache<A>::iterateCacheEntries(void (*func)(
   }
   _LIBUNWIND_LOG_IF_FALSE(_lock.unlock());
 }
+#endif
+
 #endif // defined(_LIBUNWIND_SUPPORT_DWARF_UNWIND)