[ELF] Suppress "STT_SECTION symbol should be defined" on .eh_frame, .debug*, .zdebug* and .gcc_except_table

Summary:
With -r or --emit-relocs, we warn `STT_SECTION symbol should be defined`
on relocations to discarded section symbol. This was added as an error
in rLLD319404, but was not so effective before D61583 (it turned the
error to a warning).

Relocations from .eh_frame .debug* .zdebug* .gcc_except_table to
discarded .text are very common and somewhat expected. Don't warn/error
on them. As a reference, ld.bfd has a similar logic in
_bfd_elf_default_action_discarded() to allow these cases.

Delete invalid-undef-section-symbol.test because what it intended to
check is now covered by the updated comdat-discarded-reloc.s

Delete relocatable-eh-frame.s because we allow relocations from
.eh_frame as a special case now.

Reviewers: grimar, phosek, ruiu, espindola

Reviewed By: ruiu

Subscribers: emaste, arichardson, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D62840

llvm-svn: 362497

lld/ELF/InputSection.cpp

@@ -412,7 +412,8 @@ void InputSection::copyRelocations(uint8_t *Buf, ArrayRef<RelTy> Rels) {
 
   for (const RelTy &Rel : Rels) {
     RelType Type = Rel.getType(Config->IsMips64EL);
-    Symbol &Sym = getFile<ELFT>()->getRelocTargetSym(Rel);
+    const ObjFile<ELFT> *File = getFile<ELFT>();
+    Symbol &Sym = File->getRelocTargetSym(Rel);
 
     auto *P = reinterpret_cast<typename ELFT::Rela *>(Buf);
     Buf += sizeof(RelTy);
@@ -435,10 +436,20 @@ void InputSection::copyRelocations(uint8_t *Buf, ArrayRef<RelTy> Rels) {
       // .eh_frame is horribly special and can reference discarded sections. To
       // avoid having to parse and recreate .eh_frame, we just replace any
       // relocation in it pointing to discarded sections with R_*_NONE, which
-      // hopefully creates a frame that is ignored at runtime.
+      // hopefully creates a frame that is ignored at runtime. Also, don't warn
+      // on .gcc_except_table and debug sections.
       auto *D = dyn_cast<Defined>(&Sym);
       if (!D) {
-        warn("STT_SECTION symbol should be defined");
+        if (!Sec->Name.startswith(".debug") &&
+            !Sec->Name.startswith(".zdebug") && Sec->Name != ".eh_frame" &&
+            Sec->Name != ".gcc_except_table") {
+          uint32_t SecIdx = cast<Undefined>(Sym).DiscardedSecIdx;
+          Elf_Shdr_Impl<ELFT> Sec =
+              CHECK(File->getObj().sections(), File)[SecIdx];
+          warn("relocation refers to a discarded section: " +
+               CHECK(File->getObj().getSectionName(&Sec), File) +
+               "\n>>> referenced by " + getObjMsg(P->r_offset));
+        }
         P->setSymbolAndType(0, 0, false);
         continue;
       }

lld/test/ELF/Inputs/comdat-discarded-reloc.s

@@ -1,6 +1,8 @@
-.section .text.bar1,"aG",@progbits,group,comdat
+.global bar, _start
 
-.section .text.bar2
-.global bar
-bar:
- .quad .text.bar1
+.section .text.foo,"aG",@progbits,group,comdat
+
+.section .text
+_start:
+ .quad .text.foo
+ .quad bar

lld/test/ELF/comdat-discarded-reloc.s

@@ -1,17 +1,42 @@
 # REQUIRES: x86
 # RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux %s -o %t.o
 # RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux %p/Inputs/comdat-discarded-reloc.s -o %t2.o
-# RUN: ld.lld -gc-sections --noinhibit-exec %t.o %t2.o -o /dev/null
+# RUN: ld.lld -gc-sections --noinhibit-exec %t2.o %t.o -o /dev/null
+# RUN: ld.lld -r %t2.o %t.o -o %t 2>&1 | FileCheck --check-prefix=WARN %s
+# RUN: llvm-readobj -r %t | FileCheck --check-prefix=RELOC %s
 
 ## ELF spec doesn't allow a relocation to point to a deduplicated
 ## COMDAT section. Unfortunately this happens in practice (e.g. .eh_frame)
 ## Test case checks we do not crash.
 
-.global bar, _start
+# WARN: warning: relocation refers to a discarded section: .text.bar1
+# WARN-NEXT: >>> referenced by {{.*}}.o:(.rela.text.bar2+0x0)
+# WARN-NOT: warning
 
-.section .text.foo,"aG",@progbits,group,comdat
+# RELOC:      .rela.eh_frame {
+# RELOC-NEXT:   R_X86_64_NONE
+# RELOC-NEXT: }
+# RELOC-NEXT: .rela.debug_foo {
+# RELOC-NEXT:   R_X86_64_NONE
+# RELOC-NEXT: }
+# RELOC-NEXT: .rela.gcc_except_table {
+# RELOC-NEXT:   R_X86_64_NONE
+# RELOC-NEXT: }
 
-.section .text
-_start:
- .quad .text.foo
- .quad bar
+.section .text.bar1,"aG",@progbits,group,comdat
+
+## .text.bar1 in this file is discarded. Warn on the relocation.
+.section .text.bar2,"ax"
+.globl bar
+bar:
+  .quad .text.bar1
+
+## Don't warn on .eh_frame, .debug*, .zdebug*, or .gcc_except_table
+.section .eh_frame,"a"
+  .quad .text.bar1
+
+.section .debug_foo
+  .quad .text.bar1
+
+.section .gcc_except_table,"a"
+  .quad .text.bar1

lld/test/ELF/invalid-undef-section-symbol.test

@@ -1,26 +0,0 @@
-# RUN: yaml2obj %s -o %t.o
-# RUN: not ld.lld -r --fatal-warnings %t.o -o /dev/null 2>&1 | FileCheck %s
-
-# We used to crash at this.
-# CHECK: STT_SECTION symbol should be defined
-
---- !ELF
-FileHeader:
-  Class:           ELFCLASS64
-  Data:            ELFDATA2LSB
-  Type:            ET_REL
-  Machine:         EM_X86_64
-Sections:
-  - Name:            .text
-    Type:            SHT_PROGBITS
-  - Name:            .rela.text
-    Type:            SHT_RELA
-    AddressAlign:    0x0000000000000008
-    Info:            .text
-    Relocations:
-      - Offset:          0x0000000000000000
-        Symbol:          .text
-        Type:            R_X86_64_NONE
-Symbols:
-  - Name:            .text
-    Type:            STT_SECTION

lld/test/ELF/relocatable-eh-frame.s

@@ -1,21 +0,0 @@
-# REQUIRES: x86
-# RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux %s -o %t.o
-# RUN: ld.lld -r %t.o %t.o -o %t 2>&1 | FileCheck --check-prefix=WARN %s
-# RUN: llvm-readobj -r %t | FileCheck %s
-# RUN: ld.lld %t -o %t.so -shared
-# RUN: llvm-objdump -h %t.so | FileCheck --check-prefix=DSO %s
-
-# WARN: STT_SECTION symbol should be defined
-
-# DSO: .eh_frame     00000034
-
-# CHECK:      Relocations [
-# CHECK-NEXT:   Section ({{.*}}) .rela.eh_frame {
-# CHECK-NEXT:     0x20 R_X86_64_PC32 .foo 0x0
-# CHECK-NEXT:     0x50 R_X86_64_NONE - 0x0
-# CHECK-NEXT:   }
-# CHECK-NEXT: ]
-
-.section .foo,"aG",@progbits,bar,comdat
-.cfi_startproc
-.cfi_endproc