[llvm-objcopy] Add --strip-all-gnu and change --strip-all

[jakehehrlich]

Summary

GNU's --strip-all doesn't strip as aggressively as it could in general. Currently llvm-objcopy copies the exact behavoir of GNU's --strip-all. eu-strip is used as a drop in replacement for GNU strip/objcopy in many many places without issue. eu-strip removes non-allocated sections and keeps .gnu.warning* sections. Because --strip-all will likely be the most widely used stripping option we should make --strip-all as aggressive as it can safely be. Since we have evidence from eu-strip that this is a safe option we should allow it. For those that might still have an issue afterwards I've added --strip-all-gnu as an exact drop in replacement for GNU's --strip-all as well.

[mcgrathr]

LGTM. I wonder if it's really worth keeping --strip-non-alloc.

test/tools/llvm-objcopy/strip-all-gnu.test

+# RUN: yaml2obj %s > %t
+# RUN: llvm-objcopy --strip-all-gnu %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:            .dynstr
+    Type:            SHT_STRTAB
+    Flags:           [ SHF_ALLOC ]
+  - Name:            .symtab.dyn
+    Type:            SHT_SYMTAB
+    Flags:           [ SHF_ALLOC ]
+    Type:            SHT_NOBITS
+  - Name:            .text
+    Type:            SHT_PROGBITS
+    Flags:           [ SHF_ALLOC, SHF_EXECINSTR ]
+    Size:            4
+  - Name:            .debug_info
+    Type:            SHT_PROGBITS
+    Flags:           [ ]
+    AddressAlign:    0x1
+    Size:            4
+  - Name:            .debug_loc
+    Type:            SHT_PROGBITS
+    Flags:           [ SHF_ALLOC ]
+    AddressAlign:    0x1
+    Size:            4
+  - Name:            .comment
+    Type:            SHT_PROGBITS
+  - Name:            .random_section_name
+    Type:            SHT_PROGBITS
+  - Name:            .debug_not_a_real_debug_section
+    Type:            SHT_PROGBITS
+  - Name:            .rel.text
+    Type:            SHT_REL
+    Info:            .text
+  - Name:            .rela.text
+    Type:            SHT_RELA
+    Info:            .text
+
+# CHECK: SectionHeaderCount: 8
+
+# CHECK:      Name: .dynstr
+# CHECK:      Name: .symtab.dyn
+# CHECK:      Name: .text
+# CHECK:      Name: .debug_loc
+# CHECK:      Name: .comment
+# CHECK:      Name: .random_section_name
+# CHECK:      Name: .shstrtab

test/tools/llvm-objcopy/strip-all.test

 # RUN: yaml2obj %s > %t
 # RUN: llvm-objcopy --strip-all %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:            .dynstr
-    Type:            SHT_STRTAB
-    Flags:           [ SHF_ALLOC ]
-  - Name:            .symtab.dyn
-    Type:            SHT_SYMTAB
-    Flags:           [ SHF_ALLOC ]
+  - Name:            .bss
     Type:            SHT_NOBITS
+    Flags:           [ SHF_ALLOC ]
   - Name:            .text
     Type:            SHT_PROGBITS
     Flags:           [ SHF_ALLOC, SHF_EXECINSTR ]
-    Size:            4
-  - Name:            .debug_info
+  - Name:            .blarg
     Type:            SHT_PROGBITS
     Flags:           [ ]
-    AddressAlign:    0x1
-    Size:            4
-  - Name:            .debug_loc
-    Type:            SHT_PROGBITS
-    Flags:           [ SHF_ALLOC ]
-    AddressAlign:    0x1
-    Size:            4
-  - Name:            .comment
-    Type:            SHT_PROGBITS
-  - Name:            .random_section_name
-    Type:            SHT_PROGBITS
-  - Name:            .debug_not_a_real_debug_section
+  - Name:            .gnu.warning.foo
     Type:            SHT_PROGBITS
-  - Name:            .rel.text
-    Type:            SHT_REL
-    Info:            .text
-  - Name:            .rela.text
-    Type:            SHT_RELA
-    Info:            .text
 
-# CHECK: SectionHeaderCount: 8
+# CHECK: SectionHeaderCount: 5
 
-# CHECK:      Name: .dynstr
-# CHECK:      Name: .symtab.dyn
-# CHECK:      Name: .text
-# CHECK:      Name: .debug_loc
-# CHECK:      Name: .comment
-# CHECK:      Name: .random_section_name
-# CHECK:      Name: .shstrtab
+# CHECK: Name: .bss
+# CHECK: Name: .text
+# CHECK: Name: .gnu.warning.foo
+# CHECK: Name: .shstrtab

tools/llvm-objcopy/llvm-objcopy.cpp

 static cl::opt<std::string>
     OutputFormat("O", cl::desc("Set output format to one of the following:"
                                "\n\tbinary"));
 static cl::list<std::string> ToRemove("remove-section",
                                       cl::desc("Remove <section>"),
                                       cl::value_desc("section"));
 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> StripAll(
+    "strip-all",
+    cl::desc(
+        "Removes non-allocated sections other than .gnu.warning* sections"));
+static cl::opt<bool>
+    StripAllGNU("strip-all-gnu",
 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"));
RemovePred = [RemovePred](const SectionBase &Sec) {
       return IsDWOSection(Sec) || RemovePred(Sec);
     };
 
   if (ExtractDWO)
     RemovePred = [RemovePred, &Obj](const SectionBase &Sec) {
       return OnlyKeepDWOPred(*Obj, Sec) || RemovePred(Sec);
     };
 
-  if (StripAll)
+  if (StripAllGNU)
     RemovePred = [RemovePred, &Obj](const SectionBase &Sec) {
       if (RemovePred(Sec))
         return true;
       if ((Sec.Flags & SHF_ALLOC) != 0)
         return false;
       if (&Sec == Obj->getSectionHeaderStrTab())
         return false;
       switch(Sec.Type) {
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;
     };
 
+  if (StripAll)
+    RemovePred = [RemovePred, &Obj](const SectionBase &Sec) {
+      if (RemovePred(Sec))
+        return true;
+      if (&Sec == Obj->getSectionHeaderStrTab())
+        return false;
+      if (Sec.Name.startswith(".gnu.warning"))
+        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]);