commit 6937bcd208fdea8f762198d8fadd8ac9606ec234
author Sterling Augustine <saugustine@google.com> Tue Aug 18 12:05:07 2020 -0700
committer Copybara-Service <copybara-worker@google.com> Fri Aug 28 11:18:15 2020 -0700
tree eee3c6e8b17b1ebeb571da6d16c1cc8cc99cd8b8
parent f9aeeee93e738c86130e34664f9e97b1b98c3978

Default to disabling the libunwind frameheader cache.

Although it works fine with glibc, as currently implemented the
frameheader cache is incompatible with certain platforms with
slightly different locking semantics inside dl_iterate_phdr.

Therefore only enable it when it is turned on explicitly with
a configure-time option.

Differential Revision: https://reviews.llvm.org/D86163

GitOrigin-RevId: a20f5fe70810e0a768c1814d69d10862965c21e4

CMakeLists.txt

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 8419d85..f4243f3 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -138,6 +138,7 @@
 option(LIBUNWIND_USE_COMPILER_RT "Use compiler-rt instead of libgcc" OFF)
 option(LIBUNWIND_INCLUDE_DOCS "Build the libunwind documentation." ${LLVM_INCLUDE_DOCS})
 option(LIBUNWIND_IS_BAREMETAL "Build libunwind for baremetal targets." OFF)
+option(LIBUNWIND_USE_FRAME_HEADER_CACHE "Cache frame headers for unwinding. Requires locking dl_iterate_phdr." OFF)
 
 set(LIBUNWIND_LIBDIR_SUFFIX "${LLVM_LIBDIR_SUFFIX}" CACHE STRING
     "Define suffix of library directory name (32/64)")
@@ -368,6 +369,10 @@
   add_compile_definitions(_LIBUNWIND_IS_BAREMETAL)
 endif()
 
+if(LIBUNWIND_USE_FRAME_HEADER_CACHE)
+  add_compile_definitions(_LIBUNWIND_USE_FRAME_HEADER_CACHE)
+endif()
+
 # This is the _ONLY_ place where add_definitions is called.
 if (MSVC)
   add_definitions(-D_CRT_SECURE_NO_WARNINGS)

src/AddressSpace.hpp

diff --git a/src/AddressSpace.hpp b/src/AddressSpace.hpp
index 78d2dd1..2443bd7 100644
--- a/src/AddressSpace.hpp
+++ b/src/AddressSpace.hpp
@@ -411,10 +411,12 @@
     #error "_LIBUNWIND_SUPPORT_DWARF_UNWIND requires _LIBUNWIND_SUPPORT_DWARF_INDEX on this platform."
   #endif
 
+#if defined(_LIBUNWIND_USE_FRAME_HEADER_CACHE)
 #include "FrameHeaderCache.hpp"
 
 // There should be just one of these per process.
 static FrameHeaderCache ProcessFrameHeaderCache;
+#endif
 
 static bool checkAddrInSegment(const Elf_Phdr *phdr, size_t image_base,
                                dl_iterate_cb_data *cbdata) {
@@ -435,8 +437,10 @@
   auto cbdata = static_cast<dl_iterate_cb_data *>(data);
   if (pinfo->dlpi_phnum == 0 || cbdata->targetAddr < pinfo->dlpi_addr)
     return 0;
+#if defined(_LIBUNWIND_USE_FRAME_HEADER_CACHE)
   if (ProcessFrameHeaderCache.find(pinfo, pinfo_size, data))
     return 1;
+#endif
 
   Elf_Addr image_base = calculateImageBase(pinfo);
   bool found_obj = false;
@@ -464,7 +468,9 @@
       found_obj = checkAddrInSegment(phdr, image_base, cbdata);
     }
     if (found_obj && found_hdr) {
+#if defined(_LIBUNWIND_USE_FRAME_HEADER_CACHE)
       ProcessFrameHeaderCache.add(cbdata->sects);
+#endif
       return 1;
     }
   }

test/frameheadercache_test.pass.cpp

diff --git a/test/frameheadercache_test.pass.cpp b/test/frameheadercache_test.pass.cpp
index 9397e70..ebbc004 100644
--- a/test/frameheadercache_test.pass.cpp
+++ b/test/frameheadercache_test.pass.cpp
@@ -6,7 +6,7 @@
 // The frame header cache should work fine for other architectures,
 // but the #ifdefs end up being even more complicated than this.
 
-#ifdef __x86_64__
+#if defined(__x86_64__) && defined(_LIBUNWIND_USE_FRAME_HEADER_CACHE)
 
 // This #if chain is ugly, but see the comments in AddressSpace.hpp for
 // the reasoning.