[llvm-branch-commits] [libunwind] 33c13cd - Default to disabling the libunwind frameheader cache.

[Hans Wennborg via llvm-branch-commits]

Author: Sterling Augustine
Date: 2020-08-19T16:22:51+02:00
New Revision: 33c13cd8c5772871ec79f0b061e7f7a2fb287383

URL: https://github.com/llvm/llvm-project/commit/33c13cd8c5772871ec79f0b061e7f7a2fb287383
DIFF: https://github.com/llvm/llvm-project/commit/33c13cd8c5772871ec79f0b061e7f7a2fb287383.diff

LOG: 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

(cherry picked from commit a20f5fe70810e0a768c1814d69d10862965c21e4)

Added: 
    

Modified: 
    libunwind/CMakeLists.txt
    libunwind/src/AddressSpace.hpp
    libunwind/test/frameheadercache_test.pass.cpp

Removed: 
    


################################################################################
diff  --git a/libunwind/CMakeLists.txt b/libunwind/CMakeLists.txt
index 02c130ad1bd5..bd8176c67925 100644
--- a/libunwind/CMakeLists.txt
+++ b/libunwind/CMakeLists.txt
@@ -137,6 +137,7 @@ option(LIBUNWIND_ENABLE_THREADS "Build libunwind with threading support." ON)
 option(LIBUNWIND_WEAK_PTHREAD_LIB "Use weak references to refer to pthread functions." OFF)
 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_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)")
@@ -365,6 +366,10 @@ if (LIBUNWIND_ENABLE_ARM_WMMX)
   add_compile_flags(-D__ARM_WMMX)
 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)

diff  --git a/libunwind/src/AddressSpace.hpp b/libunwind/src/AddressSpace.hpp
index a4564cb67328..e40c23291f84 100644
--- a/libunwind/src/AddressSpace.hpp
+++ b/libunwind/src/AddressSpace.hpp
@@ -452,10 +452,12 @@ struct _LIBUNWIND_HIDDEN dl_iterate_cb_data {
     #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) {
@@ -476,8 +478,10 @@ int findUnwindSectionsByPhdr(struct dl_phdr_info *pinfo, size_t pinfo_size,
   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;
@@ -505,7 +509,9 @@ int findUnwindSectionsByPhdr(struct dl_phdr_info *pinfo, size_t pinfo_size,
       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;
     }
   }

diff  --git a/libunwind/test/frameheadercache_test.pass.cpp b/libunwind/test/frameheadercache_test.pass.cpp
index 9397e70d66cb..ebbc00464e07 100644
--- a/libunwind/test/frameheadercache_test.pass.cpp
+++ b/libunwind/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.