From 7a44fe956a249585187cd5f82a0683dc117e0ae8 Mon Sep 17 00:00:00 2001
From: Reid Kleckner <rnk@google.com>
Date: Thu, 8 Nov 2018 18:38:17 +0000
Subject: [PATCH] [COFF] Improve relocation against discarded section error

Summary:
Reuse the "referenced by" note diagnostic code that we already use for
undefined symbols. In my case, it turned this:
  lld-link: error: relocation against symbol in discarded section: .text
  lld-link: error: relocation against symbol in discarded section: .text
  ...

Into this:
  lld-link: error: relocation against symbol in discarded section: .text
  >>> referenced by libANGLE.lib(CompilerGL.obj):(.SCOVP$M)
  >>> referenced by libANGLE.lib(CompilerGL.obj):(.SCOVP$M)
  ...

  lld-link: error: relocation against symbol in discarded section: .text
  >>> referenced by obj/third_party/angle/libGLESv2/entry_points_egl_ext.obj:(.SCOVP$M)
  >>> referenced by obj/third_party/angle/libGLESv2/entry_points_egl_ext.obj:(.SCOVP$M)
  ...

I think the new output is more useful.

Reviewers: ruiu, pcc

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D54240

llvm-svn: 346427
---
 lld/COFF/Chunks.cpp             | 6 ++++--
 lld/COFF/SymbolTable.cpp        | 2 +-
 lld/COFF/SymbolTable.h          | 2 ++
 lld/test/COFF/reloc-discarded.s | 1 +
 4 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/lld/COFF/Chunks.cpp b/lld/COFF/Chunks.cpp
index 9808c8be6b30..321bfeb04060 100644
--- a/lld/COFF/Chunks.cpp
+++ b/lld/COFF/Chunks.cpp
@@ -11,6 +11,7 @@
 #include "InputFiles.h"
 #include "Symbols.h"
 #include "Writer.h"
+#include "SymbolTable.h"
 #include "lld/Common/ErrorHandler.h"
 #include "llvm/ADT/Twine.h"
 #include "llvm/BinaryFormat/COFF.h"
@@ -356,7 +357,8 @@ void SectionChunk::writeTo(uint8_t *Buf) const {
       // with relocations against discarded comdat sections. Such sections
       // are left as is, with relocations untouched.
       if (!Config->MinGW)
-        error("relocation against symbol in discarded section: " + Name);
+        error("relocation against symbol in discarded section: " + Name +
+              getSymbolLocations(File, Rel.SymbolTableIndex));
       continue;
     }
     // Get the output section of the symbol for this relocation.  The output
@@ -374,7 +376,7 @@ void SectionChunk::writeTo(uint8_t *Buf) const {
       if (isCodeView() || isDWARF())
         continue;
       error("relocation against symbol in discarded section: " +
-            Sym->getName());
+            Sym->getName() + getSymbolLocations(File, Rel.SymbolTableIndex));
       continue;
     }
     uint64_t S = Sym->getRVA();
diff --git a/lld/COFF/SymbolTable.cpp b/lld/COFF/SymbolTable.cpp
index 3edd98febeeb..4a50e30e1098 100644
--- a/lld/COFF/SymbolTable.cpp
+++ b/lld/COFF/SymbolTable.cpp
@@ -84,7 +84,7 @@ static Symbol *getSymbol(SectionChunk *SC, uint32_t Addr) {
   return Candidate;
 }
 
-static std::string getSymbolLocations(ObjFile *File, uint32_t SymIndex) {
+std::string lld::coff::getSymbolLocations(ObjFile *File, uint32_t SymIndex) {
   struct Location {
     Symbol *Sym;
     std::pair<StringRef, uint32_t> FileLine;
diff --git a/lld/COFF/SymbolTable.h b/lld/COFF/SymbolTable.h
index dc40b14ff47e..00e55dbb7a02 100644
--- a/lld/COFF/SymbolTable.h
+++ b/lld/COFF/SymbolTable.h
@@ -123,6 +123,8 @@ private:
 
 extern SymbolTable *Symtab;
 
+std::string getSymbolLocations(ObjFile *File, uint32_t SymIndex);
+
 } // namespace coff
 } // namespace lld
 
diff --git a/lld/test/COFF/reloc-discarded.s b/lld/test/COFF/reloc-discarded.s
index aa8fb3c3447a..378804b62312 100644
--- a/lld/test/COFF/reloc-discarded.s
+++ b/lld/test/COFF/reloc-discarded.s
@@ -10,6 +10,7 @@
 # RUN: not lld-link -entry:main -nodefaultlib %t1.obj %t2.obj -out:%t.exe -opt:noref 2>&1 | FileCheck %s
 
 # CHECK: error: relocation against symbol in discarded section: assoc_global
+# CHECK: >>> referenced by {{.*}}reloc-discarded{{.*}}.obj:(main)
 
 	.section	.bss,"bw",discard,main_global
 	.globl	main_global