[yaml2obj][ELF] Add an optional `Size` field to the YAML section declaration.

Now the only method to configure ELF section's content and size is to assign
a hexadecimal string to the `Content` field. Unfortunately this way is
completely useless when you need to declare a really large section.

To solve this problem this patch adds one more optional field `Size`
to the `RawContentSection` structure. When yaml2obj generates an ELF file
it uses the following algorithm:
1. If both `Content` and `Size` fields are missed create an empty section.
2. If only `Content` field is missed take section length from the `Size`
   field and fill the section by zero.
3. If only `Size` field is missed create a section using data from
   the `Content` field.
4. If both `Content` and `Size` fields are provided validate that the `Size`
   value is not less than size of `Content` data. Than take section length
   from the `Size`, fill beginning of the section by `Content` and the rest
   by zero.

Examples
--------
* Create a section 0x10000 bytes long filled by zero
  Name: .data
  Type: SHT_PROGBITS
  Flags: [ SHF_ALLOC ]
  Size: 0x10000

* Create a section 0x10000 bytes long starting from 'CA' 'FE' 'BA' 'BE'
  Name: .data
  Type: SHT_PROGBITS
  Flags: [ SHF_ALLOC ]
  Content: CAFEBABE
  Size: 0x10000

The patch reviewed by Michael Spencer.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@208995 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 8 insertions, 2 deletions

diff --git a/tools/obj2yaml/elf2yaml.cpp b/tools/obj2yaml/elf2yaml.cpp
index 38afa138d9..7642921b48 100644
--- a/tools/obj2yaml/elf2yaml.cpp
+++ b/tools/obj2yaml/elf2yaml.cpp
@@ -254,6 +254,7 @@ ELFDumper<ELFT>::dumpContentSection(const Elf_Shdr *Shdr) {
   if (error_code EC = ContentOrErr.getError())
     return EC;
   S->Content = object::yaml::BinaryRef(ContentOrErr.get());
+  S->Size = S->Content.binary_size();
 
   return S.release();
 }
diff --git a/tools/yaml2obj/yaml2elf.cpp b/tools/yaml2obj/yaml2elf.cpp
index 3190b27d32..bb52cda7c1 100644
--- a/tools/yaml2obj/yaml2elf.cpp
+++ b/tools/yaml2obj/yaml2elf.cpp
@@ -314,9 +314,14 @@ void
 ELFState<ELFT>::writeSectionContent(Elf_Shdr &SHeader,
                                     const ELFYAML::RawContentSection &Section,
                                     ContiguousBlobAccumulator &CBA) {
-  Section.Content.writeAsBinary(CBA.getOSAndAlignedOffset(SHeader.sh_offset));
+  assert(Section.Size >= Section.Content.binary_size() &&
+         "Section size and section content are inconsistent");
+  raw_ostream &OS = CBA.getOSAndAlignedOffset(SHeader.sh_offset);
+  Section.Content.writeAsBinary(OS);
+  for (auto i = Section.Content.binary_size(); i < Section.Size; ++i)
+    OS.write(0);
   SHeader.sh_entsize = 0;
-  SHeader.sh_size = Section.Content.binary_size();
+  SHeader.sh_size = Section.Size;
 }
 
 template <class ELFT>