Open ELF core dumps with more than 64K sections

Summary:
Problem:

There are three filelds in the ELF header - e_phnum, e_shnum, and e_shstrndx -
that could be bigger than 64K and therefore do not fit in 16 bits reserved for
them in the header. If this happens, pretty often there is a special section at
index 0 which contains their real values for these fields in the section header
in the fields sh_info, sh_size, and sh_link respectively.

Fix:

- Rename original fields in the header declaration. We want to have them around
just in case.

- Reintroduce these fields as 32-bit members at the end of the header. By default
they are initialized from the header in Parse() method.

- In Parse(), detect the situation when the header might have been extended into
section info #0 and try to read it from the same data source.

- ObjectFileELF::GetModuleSpecifications accesses some of these fields but the
original parse uses too small data source. Re-parse the header if necessary
using bigger data source.

- ProcessElfCore::CreateInstance uses header with potentially sentinel values,
but it does not access these fields, so a comment here is enough.

Reviewers: labath

Reviewed By: labath

Subscribers: davidb, lldb-commits, mgorny

Differential Revision: https://reviews.llvm.org/D29095
Author: Eugene Birukov <eugenebi@hotmail.com>

llvm-svn: 293714

1 files changed, 62 insertions, 0 deletions

diff --git a/lldb/unittests/ObjectFile/ELF/TestELFHeader.cpp b/lldb/unittests/ObjectFile/ELF/TestELFHeader.cpp
new file mode 100644
index 00000000000..279ea0a34d3
--- /dev/null
+++ b/lldb/unittests/ObjectFile/ELF/TestELFHeader.cpp
@@ -0,0 +1,62 @@
+//===-- TestELFHeader.cpp ---------------------------------------*- C++ -*-===//
+//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "Plugins/ObjectFile/ELF/ELFHeader.h"
+#include "lldb/Core/DataExtractor.h"
+#include "gtest/gtest.h"
+
+using namespace lldb;
+using namespace lldb_private;
+
+
+TEST(ELFHeader, ParseHeaderExtension) {
+  uint8_t data[] = {
+      // e_ident
+      0x7f, 0x45, 0x4c, 0x46, 0x02, 0x01, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00,
+      0x00, 0x00, 0x00, 0x00,
+
+      // e_type, e_machine, e_version, e_entry
+      0x03, 0x00, 0x3e, 0x00, 0x01, 0x00, 0x00, 0x00, 0x90, 0x48, 0x40, 0x00,
+      0x00, 0x00, 0x00, 0x00,
+
+      // e_phoff, e_shoff
+      0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x40, 0x00, 0x00, 0x00,
+      0x00, 0x00, 0x00, 0x00,
+
+      // e_flags, e_ehsize, e_phentsize, e_phnum, e_shentsize, e_shnum,
+      // e_shstrndx
+      0x00, 0x00, 0x00, 0x00, 0x40, 0x00, 0x38, 0x00, 0xff, 0xff, 0x40, 0x00,
+      0x00, 0x00, 0xff, 0xff,
+
+      // sh_name, sh_type, sh_flags
+      0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+      0x00, 0x00, 0x00, 0x00,
+
+      // sh_addr, sh_offset
+      0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+      0x00, 0x00, 0x00, 0x00,
+
+      // sh_size, sh_link, sh_info
+      0x23, 0x45, 0x67, 0x00, 0x00, 0x00, 0x00, 0x00, 0x34, 0x56, 0x78, 0x00,
+      0x12, 0x34, 0x56, 0x00,
+
+      // sh_addralign, sh_entsize
+      0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+      0x00, 0x00, 0x00, 0x00,
+  };
+
+  DataExtractor extractor(data, sizeof data, eByteOrderLittle, 8);
+  elf::ELFHeader header;
+  offset_t offset = 0;
+  ASSERT_TRUE(header.Parse(extractor, &offset));
+  EXPECT_EQ(0x563412u, header.e_phnum);
+  EXPECT_EQ(0x785634u, header.e_shstrndx);
+  EXPECT_EQ(0x674523u, header.e_shnum);
+}