Enable reading DWARF4 CIEs with 32 bit addresses.

- Reading DWARF4 CIEs was added in
https://chromium-review.googlesource.com/c/breakpad/breakpad/+/406012 but it
was only enabled for 64bit builds, since it would error out if the CIE
address size was not 8 bytes.
- Added a unit test to ensure that 32bit continues to work.

Change-Id: I824bb40cdf12056d39da335adb55ed315970fb88
Reviewed-on: https://chromium-review.googlesource.com/c/breakpad/breakpad/+/1941034
Reviewed-by: Ivan Penkov <ivanpe@chromium.org>
Reviewed-by: Mark Mentovai <mark@chromium.org>

3 files changed, 53 insertions, 18 deletions

diff --git a/src/common/dwarf/dwarf2reader.cc b/src/common/dwarf/dwarf2reader.cc
index 27f3a83e..3e6a3e89 100644
--- a/src/common/dwarf/dwarf2reader.cc
+++ b/src/common/dwarf/dwarf2reader.cc
@@ -2330,21 +2330,15 @@ 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);
+    cie->address_size = *cursor++;
+    if (cie->address_size != 8 && cie->address_size != 4) {
+      reporter_->UnexpectedAddressSize(cie->offset, cie->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);
+    cie->segment_size = *cursor++;
+    if (cie->segment_size != 0) {
+      reporter_->UnexpectedSegmentSize(cie->offset, cie->segment_size);
       return false;
     }
   }
@@ -2606,6 +2600,15 @@ bool CallFrameInfo::Start() {
     if (!ReadCIEFields(&cie))
       continue;
 
+    // TODO(nbilling): This could lead to strange behavior if a single buffer
+    // contained a mixture of DWARF versions as well as address sizes. Not
+    // sure if it's worth handling such a case.
+
+    // DWARF4 CIE specifies address_size, so use it for this call frame.
+    if (cie.version >= 4) {
+      reader_->SetAddressSize(cie.address_size);
+    }
+
     // We now have the values that govern both the CIE and the FDE.
     cie.cie = &cie;
     fde.cie = &cie;
diff --git a/src/common/dwarf/dwarf2reader.h b/src/common/dwarf/dwarf2reader.h
index cf3ba3cd..902d9ef1 100644
--- a/src/common/dwarf/dwarf2reader.h
+++ b/src/common/dwarf/dwarf2reader.h
@@ -999,6 +999,11 @@ class CallFrameInfo {
     // or not we saw a 'z' augmentation string; its default value is
     // DW_EH_PE_absptr, which is what normal DWARF CFI uses.
     DwarfPointerEncoding pointer_encoding;
+
+    // These were only introduced in DWARF4, so will not be set in older
+    // versions.
+    uint8 address_size;
+    uint8 segment_size;
   };
 
   // A frame description entry (FDE).
diff --git a/src/common/dwarf/dwarf2reader_cfi_unittest.cc b/src/common/dwarf/dwarf2reader_cfi_unittest.cc
index 38cc7ea3..35d4f340 100644
--- a/src/common/dwarf/dwarf2reader_cfi_unittest.cc
+++ b/src/common/dwarf/dwarf2reader_cfi_unittest.cc
@@ -608,11 +608,11 @@ TEST_F(CFI, CIEVersion3ReturnColumn) {
 }
 
 TEST_F(CFI, CIEVersion4AdditionalFields) {
-  CFISection section(kBigEndian, 4);
+  CFISection section(kBigEndian, 8);
   Label cie;
   section
       .Mark(&cie)
-      // CIE version 4 with expected address and segment size.
+      // CIE version 4 with expected address (64bit) and segment size.
       .CIEHeader(0x0ab4758d, 0xc010fdf7, 0x89, 4, "", true, 8, 0)
       .FinishEntry()
       // FDE, citing that CIE.
@@ -631,7 +631,36 @@ TEST_F(CFI, CIEVersion4AdditionalFields) {
   string contents;
   EXPECT_TRUE(section.GetContents(&contents));
   ByteReader byte_reader(ENDIANNESS_BIG);
-  byte_reader.SetAddressSize(4);
+  CallFrameInfo parser(reinterpret_cast<const uint8_t *>(contents.data()),
+                       contents.size(),
+                       &byte_reader, &handler, &reporter);
+  EXPECT_TRUE(parser.Start());
+}
+
+TEST_F(CFI, CIEVersion4AdditionalFields32BitAddress) {
+  CFISection section(kBigEndian, 4);
+  Label cie;
+  section
+      .Mark(&cie)
+      // CIE version 4 with expected address (32bit) and segment size.
+      .CIEHeader(0x0ab4758d, 0xc010fdf7, 0x89, 4, "", true, 4, 0)
+      .FinishEntry()
+      // FDE, citing that CIE.
+      .FDEHeader(cie, 0x86763f2b, 0x2a66dc23)
+      .FinishEntry();
+
+  PERHAPS_WRITE_DEBUG_FRAME_FILE("CIEVersion3ReturnColumn", section);
+
+  {
+    InSequence s;
+    EXPECT_CALL(handler, Entry(_, 0x86763f2b, 0x2a66dc23, 4, "", 0x89))
+        .WillOnce(Return(true));
+    EXPECT_CALL(handler, End()).WillOnce(Return(true));
+  }
+
+  string contents;
+  EXPECT_TRUE(section.GetContents(&contents));
+  ByteReader byte_reader(ENDIANNESS_BIG);
   CallFrameInfo parser(reinterpret_cast<const uint8_t *>(contents.data()),
                        contents.size(),
                        &byte_reader, &handler, &reporter);
@@ -659,7 +688,6 @@ TEST_F(CFI, CIEVersion4AdditionalFieldsUnexpectedAddressSize) {
   string contents;
   EXPECT_TRUE(section.GetContents(&contents));
   ByteReader byte_reader(ENDIANNESS_BIG);
-  byte_reader.SetAddressSize(8);
   CallFrameInfo parser(reinterpret_cast<const uint8_t *>(contents.data()),
                        contents.size(),
                        &byte_reader, &handler, &reporter);
@@ -667,7 +695,7 @@ TEST_F(CFI, CIEVersion4AdditionalFieldsUnexpectedAddressSize) {
 }
 
 TEST_F(CFI, CIEVersion4AdditionalFieldsUnexpectedSegmentSize) {
-  CFISection section(kBigEndian, 4);
+  CFISection section(kBigEndian, 8);
   Label cie;
 
   section
@@ -685,7 +713,6 @@ TEST_F(CFI, CIEVersion4AdditionalFieldsUnexpectedSegmentSize) {
   string contents;
   EXPECT_TRUE(section.GetContents(&contents));
   ByteReader byte_reader(ENDIANNESS_BIG);
-  byte_reader.SetAddressSize(8);
   CallFrameInfo parser(reinterpret_cast<const uint8_t *>(contents.data()),
                        contents.size(),
                        &byte_reader, &handler, &reporter);