[ELF] Fix crash when .eh_frame(_hdr) is discarded

lld crashes when .eh_frame or .eh_frame_hdr section is discarded
in linker script and there is no PHDRS directive.

Differential revision: https://reviews.llvm.org/D30885

llvm-svn: 297712

lld/ELF/Writer.cpp

@@ -1355,7 +1355,8 @@ template <class ELFT> std::vector<PhdrEntry> Writer<ELFT>::createPhdrs() {
     Ret.push_back(std::move(RelRo));
 
   // PT_GNU_EH_FRAME is a special section pointing on .eh_frame_hdr.
-  if (!In<ELFT>::EhFrame->empty() && In<ELFT>::EhFrameHdr)
+  if (!In<ELFT>::EhFrame->empty() && In<ELFT>::EhFrameHdr &&
+      In<ELFT>::EhFrame->OutSec && In<ELFT>::EhFrameHdr->OutSec)
     AddHdr(PT_GNU_EH_FRAME, In<ELFT>::EhFrameHdr->OutSec->getPhdrFlags())
         ->add(In<ELFT>::EhFrameHdr->OutSec);
 

lld/test/ELF/linkerscript/pt_gnu_eh_frame.s

@@ -0,0 +1,13 @@
+# REQUIRES: x86
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t
+# RUN: echo "SECTIONS { /DISCARD/ : { *(.eh_frame*) *(.eh_frame_hdr*) } }" > %t.script
+# RUN: ld.lld -o %t1 --eh-frame-hdr --script %t.script %t
+
+.global _start
+_start:
+ nop
+
+.section .dah,"ax",@progbits
+.cfi_startproc
+ nop
+.cfi_endproc