[llvm-strip] Expose --keep-symbol option

[alexander-shaposhnikov]

Summary

Expose --keep-symbol option in llvm-strip.
Test plan: make check-all

[jakehehrlich]

LGTM

[jhenderson]

test/tools/llvm-objcopy/strip-all-and-keep-symbol.test

6

Maybe worth a quick comment saying why we copy and compare %t.

[jhenderson]

LGTM.

test/tools/llvm-objcopy/strip-all-and-keep-symbol.test

 # RUN: yaml2obj %s > %t
+# RUN: cp %t %t1
 # RUN: llvm-objcopy --strip-all --keep-symbol foo %t %t2
 # RUN: llvm-readobj -sections -symbols %t2 | FileCheck %s
 
+# RUN: cmp %t %t1
+# RUN: llvm-strip -keep-symbol=foo %t1
+# RUN: cmp %t1 %t2
+
 !ELF
 FileHeader:
   Class:           ELFCLASS64
   Data:            ELFDATA2LSB
   Type:            ET_REL
   Machine:         EM_X86_64
 Sections:
   - Name:            .text

tools/llvm-objcopy/StripOpts.td

def strip_debug : Flag<["-", "--"], "strip-debug">,
                   HelpText<"Remove debugging symbols only">;
 
 defm remove_section : Eq<"remove-section">,
                       MetaVarName<"section">,
                       HelpText<"Remove <section>">;
 
 def R : JoinedOrSeparate<["-"], "R">,
         Alias<remove_section>;
+
+defm keep_symbol : Eq<"keep-symbol">,
+                   MetaVarName<"symbol">,
+                   HelpText<"Do not remove symbol <symbol>">;
+
+def K : JoinedOrSeparate<["-"], "K">,
+        Alias<keep_symbol>;

tools/llvm-objcopy/llvm-objcopy.cpp

CopyConfig ParseStripOptions(ArrayRef<const char *> ArgsArr) {
 
   // Strip debug info only.
   Config.StripDebug = InputArgs.hasArg(STRIP_strip_debug);
   if (!Config.StripDebug)
     Config.StripAll = true;
 
   for (auto Arg : InputArgs.filtered(STRIP_remove_section))
     Config.ToRemove.push_back(Arg->getValue());
   
+  for (auto Arg : InputArgs.filtered(STRIP_keep_symbol))
+    Config.SymbolsToKeep.push_back(Arg->getValue());
+
   return Config;
 }
 
 int main(int argc, char **argv) {
   InitLLVM X(argc, argv);
   ToolName = argv[0];
   CopyConfig Config;
   if (sys::path::stem(ToolName).endswith_lower("strip"))
     Config = ParseStripOptions(makeArrayRef(argv + 1, argc));
   else
     Config = ParseObjcopyOptions(makeArrayRef(argv + 1, argc));
   ExecuteElfObjcopy(Config);
 }