[llvm-objcopy] Add -strip-non-alloc option to remove all non-allocated sections

This change adds a new flag not present in GNU objcopy that we call
--strip-non-alloc.

Differential Revision: https://reviews.llvm.org/D39926

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@318168 91177308-0d34-0410-b5e6-96231b3b80d8

test/tools/llvm-objcopy/strip-non-alloc.test

@@ -0,0 +1,26 @@
+# RUN: yaml2obj %s > %t
+# RUN: llvm-objcopy --strip-non-alloc %t %t2
+# RUN: llvm-readobj -file-headers -sections %t2 | FileCheck %s
+
+!ELF
+FileHeader:
+  Class:           ELFCLASS64
+  Data:            ELFDATA2LSB
+  Type:            ET_REL
+  Machine:         EM_X86_64
+Sections:
+  - Name:            .bss
+    Type:            SHT_NOBITS
+    Flags:           [ SHF_ALLOC ]
+  - Name:            .text
+    Type:            SHT_PROGBITS
+    Flags:           [ SHF_ALLOC, SHF_EXECINSTR ]
+  - Name:            .blarg
+    Type:            SHT_PROGBITS
+    Flags:           [ ]
+
+# CHECK: SectionHeaderCount: 4
+
+# CHECK: Name: .bss
+# CHECK: Name: .text
+# CHECK: Name: .shstrtab

tools/llvm-objcopy/llvm-objcopy.cpp

@@ -87,6 +87,8 @@ static cl::opt<bool> StripDebug("strip-debug",
                                 cl::desc("Removes all debug information"));
 static cl::opt<bool> StripSections("strip-sections",
                                    cl::desc("Remove all section headers"));
+static cl::opt<bool> StripNonAlloc("strip-non-alloc",
+                                   cl::desc("Remove all non-allocated sections"));
 static cl::opt<bool>
     StripDWO("strip-dwo", cl::desc("remove all DWARF .dwo sections from file"));
 static cl::opt<bool> ExtractDWO(
@@ -206,6 +208,15 @@ void CopyBinary(const ELFObjectFile<ELFT> &ObjFile) {
     };
   }
 
+  if (StripNonAlloc)
+    RemovePred = [RemovePred, &Obj](const SectionBase &Sec) {
+      if (RemovePred(Sec))
+        return true;
+      if (&Sec == Obj->getSectionHeaderStrTab())
+        return false;
+      return (Sec.Flags & SHF_ALLOC) == 0;
+    };
+
   Obj->removeSections(RemovePred);
   Obj->finalize();
   WriteObjectFile(*Obj, OutputFilename.getValue());