Basic handling of CIE version 4 in dwarf reading

CIE looks like it's been emitted by clang since ~May 2015 [1]. This
means that we didn't have any CFI because this parse aborted, which
meant that all stack walks reverted to stack scanning. Allow expected
values for address size and segment descriptor size through so that
dump_syms can generate at least somewhat reasonable data.

[1]: http://lists.llvm.org/pipermail/llvm-commits/Week-of-Mon-20150518/277292.html

R=mark@chromium.org
BUG=chromium:627529

Change-Id: I6dc92f51c4afd25c2adff92c09ccb8bb03bf9112
Reviewed-on: https://chromium-review.googlesource.com/406012
Reviewed-by: Mark Mentovai <mark@chromium.org>

1 files changed, 42 insertions, 6 deletions

diff --git a/src/common/dwarf/dwarf2reader.cc b/src/common/dwarf/dwarf2reader.cc
index a65b43c8..fda049dd 100644
--- a/src/common/dwarf/dwarf2reader.cc
+++ b/src/common/dwarf/dwarf2reader.cc
@@ -2253,11 +2253,11 @@ bool CallFrameInfo::ReadCIEFields(CIE *cie) {
   cursor++;
 
   // If we don't recognize the version, we can't parse any more fields of the
-  // CIE. For DWARF CFI, we handle versions 1 through 3 (there was never a
-  // version 2 of CFI data). For .eh_frame, we handle versions 1 and 3 as well;
+  // CIE. For DWARF CFI, we handle versions 1 through 4 (there was never a
+  // version 2 of CFI data). For .eh_frame, we handle versions 1 and 4 as well;
   // the difference between those versions seems to be the same as for
   // .debug_frame.
-  if (cie->version < 1 || cie->version > 3) {
+  if (cie->version < 1 || cie->version > 4) {
     reporter_->UnrecognizedVersion(cie->offset, cie->version);
     return false;
   }
@@ -2287,16 +2287,36 @@ bool CallFrameInfo::ReadCIEFields(CIE *cie) {
     }
   }
 
+  if (cie->version >= 4) {
+    uint8_t address_size = *cursor++;
+    if (address_size != 8) {
+      // TODO(scottmg): Only supporting x64 for now.
+      reporter_->UnexpectedAddressSize(cie->offset, address_size);
+      return false;
+    }
+
+    uint8_t segment_size = *cursor++;
+    if (segment_size != 0) {
+      // TODO(scottmg): Only supporting x64 for now.
+      // I would have perhaps expected 4 here, but LLVM emits a 0, near
+      // http://llvm.org/docs/doxygen/html/MCDwarf_8cpp_source.html#l00606. As
+      // we are not using the value, only succeed for now if it's the expected
+      // 0.
+      reporter_->UnexpectedSegmentSize(cie->offset, segment_size);
+      return false;
+    }
+  }
+
   // Parse the code alignment factor.
   cie->code_alignment_factor = reader_->ReadUnsignedLEB128(cursor, &len);
   if (size_t(cie->end - cursor) < len) return ReportIncomplete(cie);
   cursor += len;
-  
+
   // Parse the data alignment factor.
   cie->data_alignment_factor = reader_->ReadSignedLEB128(cursor, &len);
   if (size_t(cie->end - cursor) < len) return ReportIncomplete(cie);
   cursor += len;
-  
+
   // Parse the return address register. This is a ubyte in version 1, and
   // a ULEB128 in version 3.
   if (cie->version == 1) {
@@ -2407,7 +2427,7 @@ bool CallFrameInfo::ReadCIEFields(CIE *cie) {
 
   return true;
 }
-  
+
 bool CallFrameInfo::ReadFDEFields(FDE *fde) {
   const uint8_t *cursor = fde->fields;
   size_t size;
@@ -2648,6 +2668,22 @@ void CallFrameInfo::Reporter::BadCIEId(uint64 offset, uint64 cie_offset) {
           filename_.c_str(), offset, section_.c_str(), cie_offset);
 }
 
+void CallFrameInfo::Reporter::UnexpectedAddressSize(uint64 offset,
+                                                    uint8_t address_size) {
+  fprintf(stderr,
+          "%s: CFI frame description entry at offset 0x%llx in '%s':"
+          " CIE specifies unexpected address size: %d\n",
+          filename_.c_str(), offset, section_.c_str(), address_size);
+}
+
+void CallFrameInfo::Reporter::UnexpectedSegmentSize(uint64 offset,
+                                                    uint8_t segment_size) {
+  fprintf(stderr,
+          "%s: CFI frame description entry at offset 0x%llx in '%s':"
+          " CIE specifies unexpected segment size: %d\n",
+          filename_.c_str(), offset, section_.c_str(), segment_size);
+}
+
 void CallFrameInfo::Reporter::UnrecognizedVersion(uint64 offset, int version) {
   fprintf(stderr,
           "%s: CFI frame description entry at offset 0x%llx in '%s':"