Backout previous, the reintroduced code leads to a missing symbol

regress:
cc  -Wl,--export-dynamic  -o t_backtrace t_backtrace.o atf-c.o -lexecinfo
ld: error: undefined reference: operator new(unsigned long)
>>> referenced by /usr/lib/libexecinfo.so.4.0 (disallowed by --no-allow-shlib-undefined)

ok tb@

gnu/llvm/libunwind/src/AddressSpace.hpp

@@ -16,7 +16,6 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
-#include <sys/tree.h>
 
 #include "libunwind.h"
 #include "config.h"
@@ -153,62 +152,6 @@ struct UnwindInfoSections {
 #endif
 };
 
-class UnwindInfoSectionsCache {
-public:
-
-  struct CacheItem {
-    CacheItem(UnwindInfoSections &uis, uintptr_t pc)
-      : m_uis(uis), m_pc(pc) {
-    }
-    CacheItem(uintptr_t pc)
-      : m_pc(pc) {
-    }
-
-    UnwindInfoSections m_uis;
-    uintptr_t m_pc;
-
-    RB_ENTRY(CacheItem) entry;
-  };
-
-  typedef uintptr_t CacheItemKey;
-
-  int CacheCmp(struct CacheItem *c1, struct CacheItem *c2) {
-    return (c1->m_pc < c2->m_pc ? -1 : c1->m_pc > c2->m_pc);
-  }
-
-  UnwindInfoSectionsCache() {
-    m_head = RB_INITIALIZER(&head);
-  }
-
-  bool getUnwindInfoSectionsForPC(CacheItemKey key, UnwindInfoSections &uis) {
-    UnwindInfoSections *result = nullptr;
-    if (m_prev_req_item && m_prev_req_item->m_pc == key)
-      result = &m_prev_req_item->m_uis;
-    else {
-      struct CacheItem find(key), *res;
-      res = RB_FIND(CacheTree, &m_head, &find);
-      if (res) {
-        m_prev_req_item = res;
-        result = &res->m_uis;
-      }
-    }
-    if (result) {
-      uis = *result;
-      return true;
-    }
-    return false;
-  }
-
-  void setUnwindInfoSectionsForPC(CacheItemKey key, UnwindInfoSections &uis) {
-    CacheItem *p_item(new CacheItem(uis, key));
-    RB_INSERT(CacheTree, &m_head, p_item);
-  }
-
-private:
-  CacheItem *m_prev_req_item = nullptr;
-  RB_HEAD(CacheTree, CacheItem) m_head;
-  RB_GENERATE(CacheTree, CacheItem, entry, CacheCmp);
-};
 
 /// LocalAddressSpace is used as a template parameter to UnwindCursor when
 /// unwinding a thread in the same process.  The wrappers compile away,

gnu/llvm/libunwind/src/UnwindCursor.hpp

@@ -90,8 +90,6 @@ extern "C" _Unwind_Reason_Code __libunwind_seh_personality(
 
 namespace libunwind {
 
-static thread_local UnwindInfoSectionsCache uwis_cache;
-
 #if defined(_LIBUNWIND_SUPPORT_DWARF_UNWIND)
 /// Cache of recently found FDEs.
 template <typename A>
@@ -2602,14 +2600,7 @@ void UnwindCursor<A, R>::setInfoBasedOnIPRegister(bool isReturnAddress) {
 
   // Ask address space object to find unwind sections for this pc.
   UnwindInfoSections sects;
-  bool have_sects = false;
-  if (uwis_cache.getUnwindInfoSectionsForPC(pc, sects))
-    have_sects = true;
-  else if (_addressSpace.findUnwindSections(pc, sects)) {
-    uwis_cache.setUnwindInfoSectionsForPC(pc, sects);
-    have_sects = true;
-  }
-  if (have_sects) {
+  if (_addressSpace.findUnwindSections(pc, sects)) {
 #if defined(_LIBUNWIND_SUPPORT_COMPACT_UNWIND)
     // If there is a compact unwind encoding table, look there first.
     if (sects.compact_unwind_section != 0) {

gnu/llvm/libunwind/src/assembly.h

@@ -15,7 +15,7 @@
 #ifndef UNWIND_ASSEMBLY_H
 #define UNWIND_ASSEMBLY_H
 
-#if defined(__CET__)
+#if defined(__linux__) && defined(__CET__)
 #include <cet.h>
 #define _LIBUNWIND_CET_ENDBR _CET_ENDBR
 #else