[libunwind] Don't abort if encoutering invalid .eh_frame_hdr

Recent Linux kernel release has introduced a bug as part of the ORC
rollout where the vDSO has a valid .eh_frame section, but it's missing
the .eh_frame_hdr section and GNU_EH_FRAME segment has zero size. This
causes libunwind to abort which breaks programs that use libunwind.

The other unwinder implementation (libgcc, non-gnu) instead silently
bail out unless being compiled as debug. This change modifies libunwind
to use the same strategy.

Differential Revision: https://reviews.llvm.org/D57081

llvm-svn: 352016

2 files changed, 14 insertions, 8 deletions

diff --git a/libunwind/src/AddressSpace.hpp b/libunwind/src/AddressSpace.hpp
index 524dbaa..29a821c 100644
--- a/libunwind/src/AddressSpace.hpp
+++ b/libunwind/src/AddressSpace.hpp
@@ -535,11 +535,11 @@ inline bool LocalAddressSpace::findUnwindSections(pint_t targetAddr,
 #endif
             cbdata->sects->dwarf_index_section = eh_frame_hdr_start;
             cbdata->sects->dwarf_index_section_length = phdr->p_memsz;
-            EHHeaderParser<LocalAddressSpace>::decodeEHHdr(
+            found_hdr = EHHeaderParser<LocalAddressSpace>::decodeEHHdr(
                 *cbdata->addressSpace, eh_frame_hdr_start, phdr->p_memsz,
                 hdrInfo);
-            cbdata->sects->dwarf_section = hdrInfo.eh_frame_ptr;
-            found_hdr = true;
+            if (found_hdr)
+              cbdata->sects->dwarf_section = hdrInfo.eh_frame_ptr;
           }
         }
 
diff --git a/libunwind/src/EHHeaderParser.hpp b/libunwind/src/EHHeaderParser.hpp
index 1d53d74..0101835 100644
--- a/libunwind/src/EHHeaderParser.hpp
+++ b/libunwind/src/EHHeaderParser.hpp
@@ -35,7 +35,7 @@ public:
     uint8_t table_enc;
   };
 
-  static void decodeEHHdr(A &addressSpace, pint_t ehHdrStart, pint_t ehHdrEnd,
+  static bool decodeEHHdr(A &addressSpace, pint_t ehHdrStart, pint_t ehHdrEnd,
                           EHHeaderInfo &ehHdrInfo);
   static bool findFDE(A &addressSpace, pint_t pc, pint_t ehHdrStart,
                       uint32_t sectionLength,
@@ -52,12 +52,14 @@ private:
 };
 
 template <typename A>
-void EHHeaderParser<A>::decodeEHHdr(A &addressSpace, pint_t ehHdrStart,
+bool EHHeaderParser<A>::decodeEHHdr(A &addressSpace, pint_t ehHdrStart,
                                     pint_t ehHdrEnd, EHHeaderInfo &ehHdrInfo) {
   pint_t p = ehHdrStart;
   uint8_t version = addressSpace.get8(p++);
-  if (version != 1)
-    _LIBUNWIND_ABORT("Unsupported .eh_frame_hdr version");
+  if (version != 1) {
+    _LIBUNWIND_LOG0("Unsupported .eh_frame_hdr version");
+    return false;
+  }
 
   uint8_t eh_frame_ptr_enc = addressSpace.get8(p++);
   uint8_t fde_count_enc = addressSpace.get8(p++);
@@ -70,6 +72,8 @@ void EHHeaderParser<A>::decodeEHHdr(A &addressSpace, pint_t ehHdrStart,
           ? 0
           : addressSpace.getEncodedP(p, ehHdrEnd, fde_count_enc, ehHdrStart);
   ehHdrInfo.table = p;
+
+  return true;
 }
 
 template <typename A>
@@ -101,7 +105,9 @@ bool EHHeaderParser<A>::findFDE(A &addressSpace, pint_t pc, pint_t ehHdrStart,
   pint_t ehHdrEnd = ehHdrStart + sectionLength;
 
   EHHeaderParser<A>::EHHeaderInfo hdrInfo;
-  EHHeaderParser<A>::decodeEHHdr(addressSpace, ehHdrStart, ehHdrEnd, hdrInfo);
+  if (!EHHeaderParser<A>::decodeEHHdr(addressSpace, ehHdrStart, ehHdrEnd,
+                                      hdrInfo))
+    return false;
 
   size_t tableEntrySize = getTableEntrySize(hdrInfo.table_enc);
   pint_t tableEntry;