Enable stack trace symbolization for OSS builds (facebook#133)

Historically, HHVM statically linked the system libbfd to power
stack trace symbolization in its crash reports and in perf map files.
This was disabled for OSS in D2137703[1] because of the wildly differing libbfd ABI across
target systems. D3742004[2] and D3855027[3] then brought in
folly::Symbolizer for both use cases, but this remained gated behind a
Meta-only define.

folly::Symbolizer has been stable in upstream folly for a while now, so
let's enable it unconditionally and deshim the experimental/ header.
This also allows removing the dead libbfd integration.
For this to work, the folly build must be able to find libunwind,
which isn't a given when building against libc++ and LLVM libunwind
on Ubuntu as it installs includes into a subdirectory, so provide an
additional hint for this case.

This allows us to finally have a proper stacktrace rather than raw
memory addresses in crash reports, such as:
```
Core dumped: Segmentation fault
Stack trace in /tmp/stacktrace.902095.log
Host: hhvm-jammy-vm
ProcessID: 902095
ThreadID: 281473658339392
ThreadPID: 902095
Name: /usr/local/bin/hhvm
CmdLine: hhvm ../hhvm/hphp/test/quick/dv.php
Type: Segmentation fault
Runtime: hhvm
Version: heads/7.70.0-slack-0-g7be53eff8d22faa0383a128696fae83b224aedd5
DebuggerCount: 0

Arguments: ../hhvm/hphp/test/quick/dv.php
ThreadType: CLI

-------------------------------Treadmill Information----------------------------
Now: 235093382994348
OldestStartTime: 235093373066177
InflightRequestsSize: 1

Active Requests:
  281473658339392 1 235093373066177 (age 9ms) (timeout 0s) CLISession OLDEST

------------------------------------------------------------------------------

CPP Stacktrace:

 # 0  HPHP::jit::FixupMap::processFixupForVMFrame(HPHP::jit::VMFrame)
 # 1  HPHP::jit::FixupMap::fixupWork(HPHP::ActRec*, bool)
 # 2  HPHP::jit::detail::syncVMRegsWork(bool)
 # 3  HPHP::createBacktrace(HPHP::BacktraceArgs const&)
 # 4  HPHP::f_debug_backtrace(long, long)
 # 5  HPHP::throwable_init(HPHP::ObjectData*)
 # 6  HPHP::ObjectData* HPHP::ObjectData::newInstance<false>(HPHP::Class*)
 # 7  HPHP::SystemLib::AllocRuntimeExceptionObject(HPHP::Variant const&)
 # 8  HPHP::SystemLib::throwRuntimeExceptionObject(HPHP::Variant const&)
 # 9  HPHP::throwMissingArgument(HPHP::Func const*, int)

PHP Stacktrace:

 #0  main() called at [/home/mszabo/hhvm/hphp/test/quick/dv.php:28]
 #1  main_entry()

```

We can leverage this to augment coredumper to also provide an extract of
the stack trace in its reports, instead of having to go through the
rather onerous flow of downloading the coredump and attaching a debugger
each time.

[1] facebook@a66dd13
[2] facebook@c11ad4e
[3] https://github.com/facebook/hhvm/commits/master/hphp/runtime/vm/debug/debug.cpp

Author: mszabo-wikia

build/fbcode_builder/CMake/FindLibUnwind.cmake

@@ -12,7 +12,8 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-find_path(LIBUNWIND_INCLUDE_DIR NAMES libunwind.h)
+# When using prepackaged LLVM libunwind on Ubuntu, its includes are installed in a subdirectory.
+find_path(LIBUNWIND_INCLUDE_DIR NAMES libunwind.h PATH_SUFFIXES libunwind)
 mark_as_advanced(LIBUNWIND_INCLUDE_DIR)
 
 find_library(LIBUNWIND_LIBRARY NAMES unwind)

hphp/runtime/vm/debug/debug.cpp

@@ -25,15 +25,7 @@
 #include <stdio.h>
 #include <string.h>
 
-#if defined USE_FOLLY_SYMBOLIZER
-
-#include <folly/experimental/symbolizer/Symbolizer.h>
-
-#elif defined HAVE_LIBBFD
-
-#include <bfd.h>
-
-#endif
+#include <folly/debugging/symbolizer/Symbolizer.h>
 
 #include <folly/portability/Unistd.h>
 #include <folly/Demangle.h>
@@ -115,8 +107,6 @@ void DebugInfo::generatePidMapOverlay() {
   };
   std::vector<SymInfo> sorted;
 
-#if defined USE_FOLLY_SYMBOLIZER
-
   auto self = current_executable_path();
   using folly::symbolizer::ElfFile;
   ElfFile file;
@@ -141,51 +131,6 @@ void DebugInfo::generatePidMapOverlay() {
     return false;
   });
 
-#elif defined HAVE_LIBBFD
-
-  auto self = current_executable_path();
-  bfd* abfd = bfd_openr(self.c_str(), nullptr);
-#ifdef BFD_DECOMPRESS
-  abfd->flags |= BFD_DECOMPRESS;
-#endif
-  SCOPE_EXIT { bfd_close(abfd); };
-  char **match = nullptr;
-  if (bfd_check_format(abfd, bfd_archive) ||
-      !bfd_check_format_matches(abfd, bfd_object, &match)) {
-    return;
-  }
-
-  long storage_needed = bfd_get_symtab_upper_bound (abfd);
-
-  if (storage_needed <= 0) return;
-
-  auto symbol_table = (asymbol**)malloc(storage_needed);
-
-  SCOPE_EXIT { free(symbol_table); free(match); };
-
-  long number_of_symbols = bfd_canonicalize_symtab(abfd, symbol_table);
-
-  for (long i = 0; i < number_of_symbols; i++) {
-    auto sym = symbol_table[i];
-    if (sym->flags &
-        (BSF_INDIRECT |
-         BSF_SECTION_SYM |
-         BSF_FILE |
-         BSF_DEBUGGING_RELOC |
-         BSF_OBJECT)) {
-      continue;
-    }
-    auto sec = sym->section;
-    if (!(sec->flags & (SEC_ALLOC|SEC_LOAD|SEC_CODE))) continue;
-    auto addr = sec->vma + sym->value;
-    if (addr < uintptr_t(pidMapOverlayStart) ||
-        addr >= uintptr_t(pidMapOverlayEnd)) {
-      continue;
-    }
-    sorted.push_back(SymInfo{sym->name, addr, 0});
-  }
-#endif // HAVE_LIBBFD
-
   std::sort(
     sorted.begin(), sorted.end(),
     [](const SymInfo& a, const SymInfo& b) {

hphp/util/portability.h

@@ -190,7 +190,6 @@
 //////////////////////////////////////////////////////////////////////
 
 #ifdef HHVM_FACEBOOK
-#define USE_FOLLY_SYMBOLIZER 1
 // Linking in libbfd is a gigantic PITA, but if folly symbolizer doesn't
 // work on your platform, you'll need to figure it out.
 #define HAVE_LIBBFD 1