llvm-objcopy: Implement --extract-partition and --extract-main-partition.

This implements the functionality described in
https://lld.llvm.org/Partitions.html. It works as follows:

- Reads the section headers using the ELF header at file offset 0;
- If extracting a loadable partition:
  - Finds the section containing the required partition ELF header by looking it up in the section table;
  - Reads the ELF and program headers from the section.
- If extracting the main partition:
  - Reads the ELF and program headers from file offset 0.
- Filters the section table according to which sections are in the program headers that it read:
  - If ParentSegment != nullptr or section is not SHF_ALLOC, then it goes in.
  - Sections containing partition ELF headers or program headers are excluded as there are no headers for these in ordinary ELF files.

Differential Revision: https://reviews.llvm.org/D62364

llvm-svn: 362818

1 files changed, 11 insertions, 1 deletions

diff --git a/llvm/tools/llvm-objcopy/ELF/ELFObjcopy.cpp b/llvm/tools/llvm-objcopy/ELF/ELFObjcopy.cpp
index efb8f0582ec..adc7a9587ff 100644
--- a/llvm/tools/llvm-objcopy/ELF/ELFObjcopy.cpp
+++ b/llvm/tools/llvm-objcopy/ELF/ELFObjcopy.cpp
@@ -507,6 +507,16 @@ static Error replaceAndRemoveSections(const CopyConfig &Config, Object &Obj) {
       return (Sec.Flags & SHF_ALLOC) == 0;
     };
 
+  if (Config.ExtractPartition || Config.ExtractMainPartition) {
+    RemovePred = [RemovePred, &Obj](const SectionBase &Sec) {
+      if (RemovePred(Sec))
+        return true;
+      if (Sec.Type == SHT_LLVM_PART_EHDR || Sec.Type == SHT_LLVM_PART_PHDR)
+        return true;
+      return (Sec.Flags & SHF_ALLOC) != 0 && !Sec.ParentSegment;
+    };
+  }
+
   // Explicit copies:
   if (!Config.OnlySection.empty()) {
     RemovePred = [&Config, RemovePred, &Obj](const SectionBase &Sec) {
@@ -747,7 +757,7 @@ Error executeObjcopyOnRawBinary(const CopyConfig &Config, MemoryBuffer &In,
 
 Error executeObjcopyOnBinary(const CopyConfig &Config,
                              object::ELFObjectFileBase &In, Buffer &Out) {
-  ELFReader Reader(&In);
+  ELFReader Reader(&In, Config.ExtractPartition);
   std::unique_ptr<Object> Obj = Reader.create();
   // Prefer OutputArch (-O<format>) if set, otherwise infer it from the input.
   const ElfType OutputElfType =