[ELF] Error on relocations to STT_SECTION symbols if the sections were discarded

This is implemented by creating Undefined (instead of Defined) for such
local STT_SECTION symbols. It allows us to catch errors when there are
relocations to such discarded sections (e.g. in PR41693, ld.bfd and gold
error but we don't). Updated comdat-discarded-error.s checks we emit
friendly error message.

For relocatable-eh-frame.s, ld.lld -r a.o a.o will now error
"STT_SECTION symbol should be defined" because the section .eh_frame
refers to is now an Undefined instead of a Defined.
So I have to change `error()` to `warn()` to retain the output.

Reviewed By: ruiu

Differential Revision: https://reviews.llvm.org/D61583

llvm-svn: 361792

1 files changed, 2 insertions, 1 deletions

diff --git a/lld/ELF/InputSection.cpp b/lld/ELF/InputSection.cpp
index 07a30ed57c4..74878931afb 100644
--- a/lld/ELF/InputSection.cpp
+++ b/lld/ELF/InputSection.cpp
@@ -438,7 +438,8 @@ void InputSection::copyRelocations(uint8_t *Buf, ArrayRef<RelTy> Rels) {
       // hopefully creates a frame that is ignored at runtime.
       auto *D = dyn_cast<Defined>(&Sym);
       if (!D) {
-        error("STT_SECTION symbol should be defined");
+        warn("STT_SECTION symbol should be defined");
+        P->setSymbolAndType(0, 0, false);
         continue;
       }
       SectionBase *Section = D->Section->Repl;