[PowerPC][LLD] Fix linking weak hidden callees.

[stefanp]

Summary

It seems that linking functions that are marked as weak and hidden is no longer
working because the linker incorrectly asumes that it needs a thunk for the
call. The linker converts weak hidden functions into local functions before the
call the check if a Thunk is needed and so isWeakUndef() no longer returns true.

This patch adds a check to look for local and undef.

[MaskRay]

This fixes an assertion failure assert(sym->getVA()); in PPC64LongBranchTargetSection::writeTo for a -no-pie link.

I am still experimenting and think that we can actually simplify the condition to

if (s.isUndefined())

Let me figure out what tests need to be adjusted.

[stefanp]

MaskRay has fixed the issue with https://reviews.llvm.org/D119787

I'm going to abandon this patch.

lld/ELF/Arch/PPC64.cpp

bool PPC64::needsThunk(RelExpr expr, RelType type, const InputFile *file,
   if (type == R_PPC64_REL24_NOTOC && (s.stOther >> 5) > 1)
     return true;
 
   // If a symbol is a weak undefined and we are compiling an executable
   // it doesn't need a range-extending thunk since it can't be called.
   if (s.isUndefWeak() && !config->shared)
     return false;
 
+  // Local undefined.
+  if (s.isUndefined() && s.isLocal())
+    return false;
+
   // If the offset exceeds the range of the branch type then it will need
   // a range-extending thunk.
   // See the comment in getRelocTargetVA() about R_PPC64_CALL.
   return !inBranchRange(type, branchAddr,
                         s.getVA(a) +
                             getPPC64GlobalEntryToLocalEntryOffset(s.stOther));
 }
 

lld/test/ELF/ppc64-weak-hidden-undef.s

+# REQUIRES: ppc
+# RUN: llvm-mc -filetype=obj -triple=powerpc64le %s -o %t.o
+# RUN: ld.lld %t.o -o %t
+# RUN: llvm-objdump -d --no-show-raw-insn %t | FileCheck %s
+
+# CHECK-LABEL: <main>:
+# CHECK:         bl
+# CHECK-NEXT:    nop
+# CHECK-NEXT:    blr
+
+main:
+  bl callee
+  nop
+  blr
+
+  .hidden callee
+  .weak callee