[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.

llvm-svn: 208995

1 files changed, 9 insertions, 0 deletions

diff --git a/llvm/lib/Object/ELFYAML.cpp b/llvm/lib/Object/ELFYAML.cpp
index c396f66ee65..547720ddc32 100644
--- a/llvm/lib/Object/ELFYAML.cpp
+++ b/llvm/lib/Object/ELFYAML.cpp
@@ -658,6 +658,7 @@ static void commonSectionMapping(IO &IO, ELFYAML::Section &Section) {
 static void sectionMapping(IO &IO, ELFYAML::RawContentSection &Section) {
   commonSectionMapping(IO, Section);
   IO.mapOptional("Content", Section.Content);
+  IO.mapOptional("Size", Section.Size, Hex64(Section.Content.binary_size()));
 }
 
 static void sectionMapping(IO &IO, ELFYAML::RelocationSection &Section) {
@@ -687,6 +688,14 @@ void MappingTraits<std::unique_ptr<ELFYAML::Section>>::mapping(
   }
 }
 
+StringRef MappingTraits<std::unique_ptr<ELFYAML::Section>>::validate(
+    IO &io, std::unique_ptr<ELFYAML::Section> &Section) {
+  const auto *RawSection = dyn_cast<ELFYAML::RawContentSection>(Section.get());
+  if (!RawSection || RawSection->Size >= RawSection->Content.binary_size())
+    return StringRef();
+  return "Section size must be greater or equal to the content size";
+}
+
 void MappingTraits<ELFYAML::Relocation>::mapping(IO &IO,
                                                  ELFYAML::Relocation &Rel) {
   IO.mapRequired("Offset", Rel.Offset);