[ELF] - Improve diagnostic messages.

[grimar]

Summary

Particulaty "cannot preempt symbol" message
is extended with locations now.

[emaste]

LGTM to me as well, without "previously" as Rafael said. I'm very happy to see these improvements in diagnostic messages.

[emaste]

lld/trunk/ELF/Relocations.cpp

457

This is the "previously" that Rafael mentioned should be dropped

[grimar]

lld/trunk/ELF/Relocations.cpp

457

yes, sorry, will update in a few minutes.

lld/trunk/ELF/Relocations.cpp

if (Config->Shared || (Config->Pic && !isRelExpr(Expr))) {
     error(getLocation(S, RelOff) + ": can't create dynamic relocation " +
           getRelName(Type) + " against " +
           ((Name.empty() ? "local symbol in readonly segment"
                          : "symbol '" + Name + "'")) +
           " defined in " + getFilename(Body.File));
     return Expr;
   }
   if (Body.getVisibility() != STV_DEFAULT) {
-    error("cannot preempt symbol " + Body.getName());
+    error(getLocation(S, RelOff) + ": cannot preempt symbol '" +
+          Body.getName() + "' previously defined in " + getFilename(Body.File));
     return Expr;
   }
   if (Body.isObject()) {
     // Produce a copy relocation.
     auto *B = cast<SharedSymbol<ELFT>>(&Body);
     if (!B->needsCopy())
       addCopyRelSymbol(B);
     return Expr;
if (Body.isFunc()) {
     // the value of the symbol we created. This is true even for got entries, so
     // pointer equality is maintained. To avoid an infinite loop, the only entry
     // that points to the real function is a dedicated got entry used by the
     // plt. That is identified by special relocation types (R_X86_64_JUMP_SLOT,
     // R_386_JMP_SLOT, etc).
     Body.NeedsCopyOrPltAddr = true;
     return toPlt(Expr);
   }
-  error("symbol " + Body.getName() + " is missing type");
+  error("symbol '" + Body.getName() + "' defined in " + getFilename(Body.File) +
+        " is missing type");
 
   return Expr;
 }
 
 template <class ELFT, class RelTy>
 static typename ELFT::uint computeAddend(const elf::ObjectFile<ELFT> &File,
                                          const uint8_t *SectionData,
                                          const RelTy *End, const RelTy &RI,

lld/trunk/test/ELF/copy-errors.s

 // 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/protected-shared.s -o %t2.o
 // RUN: ld.lld %t2.o -o %t2.so -shared
 // RUN: not ld.lld %t.o %t2.so -o %t 2>&1 | FileCheck %s
 
 .global _start
 _start:
 
 
 call bar
-// CHECK: cannot preempt symbol bar
+// CHECK: {{.*}}.o (.text+0x1): cannot preempt symbol 'bar' previously defined in {{.*}}.so
 
 call zed
-// CHECK: symbol zed is missing type
+// CHECK: symbol 'zed' defined in {{.*}}.so is missing type