[PATCH] D86163: Allow enabling the libunwind frameheader cache at configure time.

[Sterling Augustine via Phabricator via llvm-commits]

saugustine created this revision.
Herald added subscribers: libcxx-commits, llvm-commits, mgorny.
Herald added projects: LLVM, libunwind.
Herald added a reviewer: libunwind.
saugustine requested review of this revision.

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.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D86163

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


Index: libunwind/test/frameheadercache_test.pass.cpp
===================================================================
--- libunwind/test/frameheadercache_test.pass.cpp
+++ 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_FRAMEHEADER_CACHE)
 
 // This #if chain is ugly, but see the comments in AddressSpace.hpp for
 // the reasoning.
Index: libunwind/src/AddressSpace.hpp
===================================================================
--- libunwind/src/AddressSpace.hpp
+++ libunwind/src/AddressSpace.hpp
@@ -411,10 +411,13 @@
     #error "_LIBUNWIND_SUPPORT_DWARF_UNWIND requires _LIBUNWIND_SUPPORT_DWARF_INDEX on this platform."
   #endif
 
+#if defined(_LIBUNWIND_USE_FRAMEHEADER_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 +438,10 @@
   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_FRAMEHEADER_CACHE)
   if (ProcessFrameHeaderCache.find(pinfo, pinfo_size, data))
     return 1;
+#endif
 
   Elf_Addr image_base = calculateImageBase(pinfo);
   bool found_obj = false;
@@ -464,7 +469,9 @@
       found_obj = checkAddrInSegment(phdr, image_base, cbdata);
     }
     if (found_obj && found_hdr) {
+#if defined(_LIBUNWIND_USE_FRAMEHEADER_CACHE)
       ProcessFrameHeaderCache.add(cbdata->sects);
+#endif
       return 1;
     }
   }
Index: libunwind/CMakeLists.txt
===================================================================
--- libunwind/CMakeLists.txt
+++ libunwind/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_FRAMEHEADER_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_FRAMEHEADER_CACHE)
+  add_compile_definitions(_LIBUNWIND_USE_FRAMEHEADER_CACHE)
+endif()
+
 # This is the _ONLY_ place where add_definitions is called.
 if (MSVC)
   add_definitions(-D_CRT_SECURE_NO_WARNINGS)


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D86163.286368.patch
Type: text/x-patch
Size: 2813 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20200818/50944a11/attachment.bin>