base: Add byte order attribute for object files

This adds byte order as an attribute for object files by
introducing new members to the ObjectFile class. This is
populated by the looking at the ELF headers.

Change-Id: Ibe55699175cc0295e0c9d49bdbe02e580988bc4f
Signed-off-by: Sandipan Das <sandipan@linux.ibm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/40939
Reviewed-by: Daniel Carvalho <odanrc@yahoo.com.br>
Maintainer: Daniel Carvalho <odanrc@yahoo.com.br>
Tested-by: kokoro <noreply+kokoro@google.com>

src/base/loader/elf_object.cc

@@ -114,6 +114,7 @@ ElfObject::ElfObject(ImageFileDataPtr ifd) : ObjectFile(ifd)
 
     determineArch();
     determineOpSys();
+    determineByteOrder();
 
     entry = ehdr.e_entry;
     _programHeaderCount = ehdr.e_phnum;
@@ -325,6 +326,15 @@ ElfObject::determineOpSys()
     }
 }
 
+void
+ElfObject::determineByteOrder()
+{
+    auto edata = ehdr.e_ident[EI_DATA];
+    if (edata == ELFDATANONE)
+        panic("invalid ELF data encoding");
+    byteOrder = (edata == ELFDATA2MSB) ? ByteOrder::big : ByteOrder::little;
+}
+
 void
 ElfObject::handleLoadableSegment(GElf_Phdr phdr, int seg_num)
 {

src/base/loader/elf_object.hh

@@ -66,6 +66,7 @@ class ElfObject : public ObjectFile
 
     void determineArch();
     void determineOpSys();
+    void determineByteOrder();
     void handleLoadableSegment(GElf_Phdr phdr, int seg_num);
 
     // These values are provided to a linux process by the kernel, so we

src/base/loader/object_file.hh

@@ -38,6 +38,7 @@
 #include "base/loader/symtab.hh"
 #include "base/logging.hh"
 #include "base/types.hh"
+#include "enums/ByteOrder.hh"
 
 GEM5_DEPRECATED_NAMESPACE(Loader, loader);
 namespace loader
@@ -80,6 +81,7 @@ class ObjectFile : public ImageFile
   protected:
     Arch arch = UnknownArch;
     OpSys opSys = UnknownOpSys;
+    ByteOrder byteOrder = ByteOrder::little;
 
     SymbolTable _symtab;
 
@@ -106,6 +108,7 @@ class ObjectFile : public ImageFile
 
     Arch  getArch()  const { return arch; }
     OpSys getOpSys() const { return opSys; }
+    ByteOrder getByteOrder() const { return byteOrder; }
 
     const SymbolTable &symtab() const { return _symtab; }