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

[jakehehrlich]

Summary

This change adds a new flag not present in GNU objcopy that I call --only-keep-alloc.

[jhenderson]

Test case?

tools/llvm-objcopy/llvm-objcopy.cpp

90

I feel like "strip-nonalloc" (or "strip-non-alloc") would be a better option name, personally, as it's more consistent with other options.

[jakehehrlich]

1. Added test (derp, it turns out I wrote it but didn't run git add on it so it didn't make it into the diff)
2. renamed "only-keep-alloc" with "strip-non-alloc" everywhere.

[jhenderson]

LGTM.

[MaskRay]

--strip-non-alloc keeps .strtab but --strip-sections does not. Is this the only difference of them?

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

+# 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

 static cl::alias ToRemoveA("R", cl::desc("Alias for remove-section"),
                            cl::aliasopt(ToRemove));
 static cl::opt<bool> StripAll("strip-all",
                               cl::desc("Removes symbol, relocation, and debug information"));
 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(
     "extract-dwo",
     cl::desc("remove all sections that are not DWARF .dwo sections from file"));
 static cl::opt<std::string>
     SplitDWO("split-dwo",
              cl::desc("equivalent to extract-dwo on the input file to "
void CopyBinary(const ELFObjectFile<ELF64LE> &ObjFile) {
   }
 
   if (StripDebug) {
     RemovePred = [RemovePred](const SectionBase &Sec) {
       return RemovePred(Sec) || Sec.Name.startswith(".debug");
     };
   }
 
+  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());
 }
 
 int main(int argc, char **argv) {
   // Print a stack trace if we signal out.
   sys::PrintStackTraceOnErrorSignal(argv[0]);