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, 20 insertions, 5 deletions

diff --git a/lldb/source/Plugins/ObjectFile/ELF/ObjectFileELF.cpp b/lldb/source/Plugins/ObjectFile/ELF/ObjectFileELF.cpp
index fa79b24c481..44ea01dbe16 100644
--- a/lldb/source/Plugins/ObjectFile/ELF/ObjectFileELF.cpp
+++ b/lldb/source/Plugins/ObjectFile/ELF/ObjectFileELF.cpp
@@ -610,7 +610,8 @@ size_t ObjectFileELF::GetModuleSpecifications(
     DataExtractor data;
     data.SetData(data_sp);
     elf::ELFHeader header;
-    if (header.Parse(data, &data_offset)) {
+    lldb::offset_t header_offset = data_offset;
+    if (header.Parse(data, &header_offset)) {
       if (data_sp) {
         ModuleSpec spec(file);
 
@@ -645,10 +646,24 @@ size_t ObjectFileELF::GetModuleSpecifications(
                           __FUNCTION__, file.GetPath().c_str());
           }
 
+          // In case there is header extension in the section #0, the header
+          // we parsed above could have sentinel values for e_phnum, e_shnum,
+          // and e_shstrndx.  In this case we need to reparse the header
+          // with a bigger data source to get the actual values.
+          size_t section_header_end = header.e_shoff + header.e_shentsize;
+          if (header.HasHeaderExtension() &&
+            section_header_end > data_sp->GetByteSize()) {
+            data_sp = file.MemoryMapFileContentsIfLocal (file_offset,
+                                                         section_header_end);
+            data.SetData(data_sp);
+            lldb::offset_t header_offset = data_offset;
+            header.Parse(data, &header_offset);
+          }
+
           // Try to get the UUID from the section list. Usually that's at the
           // end, so
           // map the file in if we don't have it already.
-          size_t section_header_end =
+          section_header_end =
               header.e_shoff + header.e_shnum * header.e_shentsize;
           if (section_header_end > data_sp->GetByteSize()) {
             data_sp = file.MemoryMapFileContentsIfLocal(file_offset,
@@ -3067,10 +3082,10 @@ void ObjectFileELF::DumpELFHeader(Stream *s, const ELFHeader &header) {
   s->Printf("e_flags     = 0x%8.8x\n", header.e_flags);
   s->Printf("e_ehsize    = 0x%4.4x\n", header.e_ehsize);
   s->Printf("e_phentsize = 0x%4.4x\n", header.e_phentsize);
-  s->Printf("e_phnum     = 0x%4.4x\n", header.e_phnum);
+  s->Printf("e_phnum     = 0x%8.8x\n", header.e_phnum);
   s->Printf("e_shentsize = 0x%4.4x\n", header.e_shentsize);
-  s->Printf("e_shnum     = 0x%4.4x\n", header.e_shnum);
-  s->Printf("e_shstrndx  = 0x%4.4x\n", header.e_shstrndx);
+  s->Printf("e_shnum     = 0x%8.8x\n", header.e_shnum);
+  s->Printf("e_shstrndx  = 0x%8.8x\n", header.e_shstrndx);
 }
 
 //----------------------------------------------------------------------