[llvm-objcopy] - Strip sections before symbols.

This is a fix for https://bugs.llvm.org/show_bug.cgi?id=40007.

Idea is to swap the order of stripping. So that we strip sections before
symbols what allows us to strip relocation sections without emitting
the error about relative symbols.

Differential revision: https://reviews.llvm.org/D59763

llvm-svn: 357017

Author: George Rimar

llvm/test/tools/llvm-objcopy/ELF/strip-symbol-and-relocation.test

@@ -0,0 +1,48 @@
+# RUN: yaml2obj %s > %t
+
+## Check we are able to strip all symbols and relocatable information at the same time.
+
+# RUN: llvm-objcopy -S %t %t2
+# RUN: llvm-objdump --section-headers %t2 | FileCheck %s
+
+# RUN: llvm-objcopy --strip-all-gnu %t %t2
+# RUN: llvm-objdump --section-headers %t2 | FileCheck %s
+
+# CHECK-NOT: .symtab
+# CHECK-NOT: .rela.text
+
+## Check we are able to strip the particular symbol if we
+## strip the corresponding relocation section at the same time.
+
+# RUN: llvm-objcopy --strip-symbol=bar -R .rela.text %t %t2
+# RUN: llvm-readelf -s -S %t2 | FileCheck %s --check-prefix=STRIPSYM
+
+# STRIPSYM-NOT: bar
+# STRIPSYM-NOT: .rela.text
+
+# RUN: not llvm-objcopy --strip-symbol=bar %t %t2 2>&1 | FileCheck %s --check-prefix=ERR
+# ERR: not stripping symbol 'bar' because it is named in a relocation
+
+--- !ELF
+FileHeader:
+  Class:           ELFCLASS64
+  Data:            ELFDATA2LSB
+  Type:            ET_REL
+  Machine:         EM_X86_64
+Sections:
+  - Name:            .text
+    Type:            SHT_PROGBITS
+    Flags:           [ SHF_ALLOC, SHF_EXECINSTR ] 
+    Content:         00000000
+  - Name:            .rela.text
+    Type:            SHT_RELA
+    Link:            .symtab
+    Info:            .text
+    Relocations:
+      - Offset:          0x0000000000000000
+        Symbol:          bar
+        Type:            R_X86_64_32S
+Symbols:
+  Global:
+    - Name:     bar
+      Section:  .text

llvm/tools/llvm-objcopy/ELF/ELFObjcopy.cpp

@@ -542,10 +542,14 @@ static Error handleArgs(const CopyConfig &Config, Object &Obj,
     Obj.OSABI = Config.OutputArch.getValue().OSABI;
   }
 
-  if (Error E = updateAndRemoveSymbols(Config, Obj))
+  // It is important to remove the sections first. For example, we want to
+  // remove the relocation sections before removing the symbols. That allows
+  // us to avoid reporting the inappropriate errors about removing symbols
+  // named in relocations.
+  if (Error E = replaceAndRemoveSections(Config, Obj))
     return E;
 
-  if (Error E = replaceAndRemoveSections(Config, Obj))
+  if (Error E = updateAndRemoveSymbols(Config, Obj))
     return E;
 
   if (!Config.SectionsToRename.empty()) {