svn commit: r364263 - projects/clang1100-import/contrib/llvm-project/libunwind/src

[Dimitry Andric]

Author: dim
Date: Sat Aug 15 22:58:07 2020
New Revision: 364263
URL: https://svnweb.freebsd.org/changeset/base/364263

Log:
  Temporarily disable libunwind's FrameHeaderCache, until there is a
  resolution for <https://bugs.llvm.org/show_bug.cgi?id=47181>.
  
  The cache implementation depends on dl_iterate_phdr(3) ensuring that its
  callbacks are not called simultaneously for multiple threads, but that
  is only the case for the dl_iterate_phdr() implementation in rtld.
  
  In a statically linked executable, libc's dl_iterate_phdr() is used,
  which does no such locking. If multiple threads then call into the
  unwinder at the same time, it is possible to trigger a segfault.
  
  In particular, the statically linked lld which is built during the
  cross-tools stage can segfault in this way, because it starts multiple
  worker threads that can exit in parallel. Since our pthread_exit(3)
  invokes the unwinder, it will therefore call into it in parallel too.

Modified:
  projects/clang1100-import/contrib/llvm-project/libunwind/src/AddressSpace.hpp

Modified: projects/clang1100-import/contrib/llvm-project/libunwind/src/AddressSpace.hpp
==============================================================================
--- projects/clang1100-import/contrib/llvm-project/libunwind/src/AddressSpace.hpp	Sat Aug 15 21:40:36 2020	(r364262)
+++ projects/clang1100-import/contrib/llvm-project/libunwind/src/AddressSpace.hpp	Sat Aug 15 22:58:07 2020	(r364263)
@@ -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 // _LIBUNWIND_USE_FRAME_HEADER_CACHE
 
 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 *pinf
   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 // _LIBUNWIND_USE_FRAME_HEADER_CACHE
 
   Elf_Addr image_base = calculateImageBase(pinfo);
   bool found_obj = false;
@@ -505,7 +509,9 @@ int findUnwindSectionsByPhdr(struct dl_phdr_info *pinf
       found_obj = checkAddrInSegment(phdr, image_base, cbdata);
     }
     if (found_obj && found_hdr) {
+#if defined(_LIBUNWIND_USE_FRAME_HEADER_CACHE)
       ProcessFrameHeaderCache.add(cbdata->sects);
+#endif // _LIBUNWIND_USE_FRAME_HEADER_CACHE
       return 1;
     }
   }