tools/llvm-objcopy/COFF/COFFObjcopy.cpp

   1 //===- COFFObjcopy.cpp ----------------------------------------------------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8
   9 #include "COFFObjcopy.h"
  10 #include "Buffer.h"
  11 #include "CopyConfig.h"
  12 #include "Object.h"
  13 #include "Reader.h"
  14 #include "Writer.h"
  15 #include "llvm-objcopy.h"
  16
  17 #include "llvm/Object/Binary.h"
  18 #include "llvm/Object/COFF.h"
  19 #include "llvm/Support/Errc.h"
  20 #include <cassert>
  21
  22 namespace llvm {
  23 namespace objcopy {
  24 namespace coff {
  25
  26 using namespace object;
  27 using namespace COFF;
  28
  29 static bool isDebugSection(const Section &Sec) {
  30   return Sec.Name.startswith(".debug");
  31 }
  32
  33 static Error handleArgs(const CopyConfig &Config, Object &Obj) {
  34   // Perform the actual section removals.
  35   Obj.removeSections([&Config](const Section &Sec) {
  36     if (Config.StripDebug || Config.StripAll || Config.StripAllGNU ||
  37         Config.DiscardAll || Config.StripUnneeded) {
  38       if (isDebugSection(Sec) &&
  39           (Sec.Header.Characteristics & IMAGE_SCN_MEM_DISCARDABLE) != 0)
  40         return true;
  41     }
  42
  43     if (is_contained(Config.ToRemove, Sec.Name))
  44       return true;
  45
  46     return false;
  47   });
  48
  49   if (Config.OnlyKeepDebug) {
  50     // For --only-keep-debug, we keep all other sections, but remove their
  51     // content. The VirtualSize field in the section header is kept intact.
  52     Obj.truncateSections([](const Section &Sec) {
  53       return !isDebugSection(Sec) && Sec.Name != ".buildid" &&
  54              ((Sec.Header.Characteristics &
  55                (IMAGE_SCN_CNT_CODE | IMAGE_SCN_CNT_INITIALIZED_DATA)) != 0);
  56     });
  57   }
  58
  59   // StripAll removes all symbols and thus also removes all relocations.
  60   if (Config.StripAll || Config.StripAllGNU)
  61     for (Section &Sec : Obj.getMutableSections())
  62       Sec.Relocs.clear();
  63
  64   // If we need to do per-symbol removals, initialize the Referenced field.
  65   if (Config.StripUnneeded || Config.DiscardAll ||
  66       !Config.SymbolsToRemove.empty())
  67     if (Error E = Obj.markSymbols())
  68       return E;
  69
  70   // Actually do removals of symbols.
  71   Obj.removeSymbols([&](const Symbol &Sym) {
  72     // For StripAll, all relocations have been stripped and we remove all
  73     // symbols.
  74     if (Config.StripAll || Config.StripAllGNU)
  75       return true;
  76
  77     if (is_contained(Config.SymbolsToRemove, Sym.Name)) {
  78       // Explicitly removing a referenced symbol is an error.
  79       if (Sym.Referenced)
  80         reportError(Config.OutputFilename,
  81                     make_error<StringError>(
  82                         "not stripping symbol '" + Sym.Name +
  83                             "' because it is named in a relocation.",
  84                         llvm::errc::invalid_argument));
  85       return true;
  86     }
  87
  88     if (!Sym.Referenced) {
  89       // With --strip-unneeded, GNU objcopy removes all unreferenced local
  90       // symbols, and any unreferenced undefined external.
  91       if (Config.StripUnneeded &&
  92           (Sym.Sym.StorageClass == IMAGE_SYM_CLASS_STATIC ||
  93            Sym.Sym.SectionNumber == 0))
  94         return true;
  95
  96       // GNU objcopy keeps referenced local symbols and external symbols
  97       // if --discard-all is set, similar to what --strip-unneeded does,
  98       // but undefined local symbols are kept when --discard-all is set.
  99       if (Config.DiscardAll && Sym.Sym.StorageClass == IMAGE_SYM_CLASS_STATIC &&
 100           Sym.Sym.SectionNumber != 0)
 101         return true;
 102     }
 103
 104     return false;
 105   });
 106   return Error::success();
 107 }
 108
 109 void executeObjcopyOnBinary(const CopyConfig &Config,
 110                             COFFObjectFile &In, Buffer &Out) {
 111   COFFReader Reader(In);
 112   Expected<std::unique_ptr<Object>> ObjOrErr = Reader.create();
 113   if (!ObjOrErr)
 114     reportError(Config.InputFilename, ObjOrErr.takeError());
 115   Object *Obj = ObjOrErr->get();
 116   assert(Obj && "Unable to deserialize COFF object");
 117   if (Error E = handleArgs(Config, *Obj))
 118     reportError(Config.InputFilename, std::move(E));
 119   COFFWriter Writer(*Obj, Out);
 120   if (Error E = Writer.write())
 121     reportError(Config.OutputFilename, std::move(E));
 122 }
 123
 124 } // end namespace coff
 125 } // end namespace objcopy
 126 } // end namespace llvm