[PATCH] D24837: [ELF] Emit a diagnostic if there's reference to a local symbol in a discarded COMDAT section

[Davide Italiano via llvm-commits]

davide created this revision.
davide added reviewers: ruiu, rafael.
davide added a subscriber: llvm-commits.

Continuing the discussion from: https://reviews.llvm.org/D24750


https://reviews.llvm.org/D24837

Files:
  ELF/Relocations.cpp
  test/ELF/comdat.s

Index: test/ELF/comdat.s
===================================================================
--- test/ELF/comdat.s
+++ test/ELF/comdat.s
@@ -1,14 +1,16 @@
 // 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.s -o %t2.o
-// RUN: ld.lld -shared %t.o %t.o %t2.o -o %t
+// RUN: ld.lld -shared %t.o %t.o %t2.o -o %t 2>&1 | FileCheck --check-prefix=WARN %s
 // RUN: llvm-objdump -d %t | FileCheck %s
 // RUN: llvm-readobj -s -t %t | FileCheck --check-prefix=READ %s
 // REQUIRES: x86
 
         .section	.text2,"axG", at progbits,foo,comdat,unique,0
 foo:
         nop
 
+// WARN: relocation from {{.*}}comdat.s{{.*}}.o with offset 1 refers to discarded section
+
 // CHECK: Disassembly of section .text2:
 // CHECK-NEXT: foo:
 // CHECK-NEXT:   1000: {{.*}}  nop
Index: ELF/Relocations.cpp
===================================================================
--- ELF/Relocations.cpp
+++ ELF/Relocations.cpp
@@ -561,6 +561,15 @@
            (PieceI->InputOff + PieceI->size() <= RI.r_offset))
       ++PieceI;
 
+    // If this a reference to a local symbol in a discarded COMDAT section,
+    // emit a warning.
+    if (Body.isLocal()) {
+      auto *D = dyn_cast<DefinedRegular<ELFT>>(&Body);
+      if (D && D->Section == &InputSection<ELFT>::Discarded)
+        warning("relocation from " + File.getName() + " with offset " +
+                Twine(RI.r_offset) + " refers to discarded section");
+    }
+
     // Compute the offset of this section in the output section. We do it here
     // to try to compute it only once.
     uintX_t Offset;


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