[ELF] Discard input .note.gnu.build-id even with default --build-id=none

[MaskRay]

Summary

binutils 2.38 will adopt this behavior
https://sourceware.org/bugzilla/show_bug.cgi?id=28639

[ikudrin]

LGTM.

lld/test/ELF/relocatable-build-id.s

8

I'd prefer to have an additional test with an explicit --build-id=none here.

[MaskRay]

add explicit --build-id=none test

[ikudrin]

lld/test/ELF/relocatable-build-id.s

10–12

[peter.smith]

LGTM too.

[MaskRay]

Update

lld/ELF/InputFiles.cpp

InputSectionBase *ObjFile<ELFT>::createInputSection(uint32_t idx,
   // files contain definitions of symbol "__x86.get_pc_thunk.bx" in linkonce
   // sections. Drop those sections to avoid duplicate symbol errors.
   // FIXME: This is glibc PR20543, we should remove this hack once that has been
   // fixed for a while.
   if (name == ".gnu.linkonce.t.__x86.get_pc_thunk.bx" ||
       name == ".gnu.linkonce.t.__i686.get_pc_thunk.bx")
     return &InputSection::discarded;
 
-  // If we are creating a new .build-id section, strip existing .build-id
-  // sections so that the output won't have more than one .build-id.
-  // This is not usually a problem because input object files normally don't
-  // have .build-id sections, but you can create such files by
-  // "ld.{bfd,gold,lld} -r --build-id", and we want to guard against it.
-  if (name == ".note.gnu.build-id" && config->buildId != BuildIdKind::None)
+  // Strip existing .note.gnu.build-id sections so that the output won't have
+  // more than one build-id. This is not usually a problem because input object
+  // files normally don't have .build-id sections, but you can create such files
+  // by "ld.{bfd,gold,lld} -r --build-id", and we want to guard against it.
+  if (name == ".note.gnu.build-id")
     return &InputSection::discarded;
 
   // The linker merges EH (exception handling) frames and creates a
   // .eh_frame_hdr section for runtime. So we handle them with a special
   // class. For relocatable outputs, they are just passed through.
   if (name == ".eh_frame" && !config->relocatable)
     return make<EhInputSection>(*this, sec, name);
 

lld/test/ELF/relocatable-build-id.s

 # REQUIRES: x86
 # RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t1.o
 # RUN: ld.lld --build-id=0xcafebabe -o %t2.o %t1.o -r
 # RUN: ld.lld --build-id=0xdeadbeef -o %t.exe %t2.o
 # RUN: llvm-objdump -s %t.exe | FileCheck %s
 
+## The default --build-id=none removes .note.gnu.build-id input sections.
+# RUN: ld.lld %t2.o -o %t.none
+# RUN: llvm-readelf -S %t.none | FileCheck %s --check-prefix=NO
+# RUN: ld.lld --build-id=none %t2.o -o %t.none2
+# RUN: cmp %t.none %t.none2
+
+# CHECK: Contents of section .note.gnu.build-id:
 # CHECK-NOT: cafebabe
 # CHECK: deadbeef
 
+# NO:     Section Headers:
+# NO-NOT: .note.gnu.build-id
+
 .global _start
 _start:
   ret