[llvm] r361642 - [llvm-objcopy] - Strip undefined symbols if they are no longer referenced following --only-section

[George Rimar via llvm-commits]

Author: grimar
Date: Fri May 24 08:04:50 2019
New Revision: 361642

URL: http://llvm.org/viewvc/llvm-project?rev=361642&view=rev
Log:
[llvm-objcopy] - Strip undefined symbols if they are no longer referenced following --only-section

This is https://bugs.llvm.org/show_bug.cgi?id=40004.

In this patch I teach llvm-objcopy to remove undefined symbols if
them are not used anymore after applying -j/--only-section option.

Differential revision: https://reviews.llvm.org/D62317

Added:
    llvm/trunk/test/tools/llvm-objcopy/ELF/only-section-strip-undefined.test
Modified:
    llvm/trunk/tools/llvm-objcopy/ELF/ELFObjcopy.cpp

Added: llvm/trunk/test/tools/llvm-objcopy/ELF/only-section-strip-undefined.test
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/tools/llvm-objcopy/ELF/only-section-strip-undefined.test?rev=361642&view=auto
==============================================================================
--- llvm/trunk/test/tools/llvm-objcopy/ELF/only-section-strip-undefined.test (added)
+++ llvm/trunk/test/tools/llvm-objcopy/ELF/only-section-strip-undefined.test Fri May 24 08:04:50 2019
@@ -0,0 +1,60 @@
+## Here we want to check that llvm-objcopy removes an undefined symbol
+## if all references to it have been stripped.
+
+# RUN: yaml2obj --docnum=1 %s -o %t.o
+# RUN: llvm-objcopy -j .other.section %t.o %t2.o
+# RUN: llvm-readobj --symbols %t2.o | FileCheck %s --implicit-check-not=bar
+
+# RUN: llvm-objcopy -j .text -j .rela.text1 %t.o %t2.o
+# RUN: llvm-readobj --symbols %t2.o | FileCheck %s --check-prefix=BAR
+
+# BAR: bar
+
+--- !ELF
+FileHeader:
+  Class:   ELFCLASS64
+  Data:    ELFDATA2LSB
+  Type:    ET_REL
+  Machine: EM_X86_64
+Sections:
+  - Name:        .text
+    Type:        SHT_PROGBITS
+  - Name:        .rela.text1
+    Type:        SHT_RELA
+    Relocations:
+      - Offset:  0x0000000000000001
+        Symbol:  bar
+        Type:    R_X86_64_32
+  - Name:        .rela.text2
+    Type:        SHT_RELA
+    Relocations:
+      - Offset:  0x0000000000000001
+        Symbol:  bar
+        Type:    R_X86_64_32
+  - Name:        .other.section
+    Type:        SHT_PROGBITS
+Symbols:
+  - Name:    bar
+    Binding: STB_GLOBAL
+...
+
+## Check we remove unreferenced undefined symbols, even if
+## they weren't previously referenced. This follows GNU.
+
+# RUN: yaml2obj --docnum=2 %s -o %t.o
+# RUN: llvm-objcopy -j .keep_me %t.o %t2.o
+# RUN: llvm-readobj --symbols %t2.o | FileCheck %s --implicit-check-not=bar
+
+--- !ELF
+FileHeader:
+  Class:   ELFCLASS64
+  Data:    ELFDATA2LSB
+  Type:    ET_REL
+  Machine: EM_X86_64
+Sections:
+  - Name: .keep_me
+    Type: SHT_PROGBITS
+Symbols:
+  - Name:    bar
+    Binding: STB_GLOBAL
+...

Modified: llvm/trunk/tools/llvm-objcopy/ELF/ELFObjcopy.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/tools/llvm-objcopy/ELF/ELFObjcopy.cpp?rev=361642&r1=361641&r2=361642&view=diff
==============================================================================
--- llvm/trunk/tools/llvm-objcopy/ELF/ELFObjcopy.cpp (original)
+++ llvm/trunk/tools/llvm-objcopy/ELF/ELFObjcopy.cpp Fri May 24 08:04:50 2019
@@ -387,7 +387,8 @@ static Error updateAndRemoveSymbols(cons
   // The purpose of this loop is to mark symbols referenced by sections
   // (like GroupSection or RelocationSection). This way, we know which
   // symbols are still 'needed' and which are not.
-  if (Config.StripUnneeded || !Config.UnneededSymbolsToRemove.empty()) {
+  if (Config.StripUnneeded || !Config.UnneededSymbolsToRemove.empty() ||
+      !Config.OnlySection.empty()) {
     for (auto &Section : Obj.sections())
       Section.markSymbols();
   }
@@ -415,6 +416,11 @@ static Error updateAndRemoveSymbols(cons
         isUnneededSymbol(Sym))
       return true;
 
+    // We want to remove undefined symbols if all references have been stripped.
+    if (!Config.OnlySection.empty() && !Sym.Referenced &&
+        Sym.getShndx() == SHN_UNDEF)
+      return true;
+
     return false;
   };