From bf9c8636f2cd1c5e6338402b67de06f9ce74cdd9 Mon Sep 17 00:00:00 2001
From: Fangrui Song <i@maskray.me>
Date: Wed, 12 Jan 2022 11:55:22 -0800
Subject: [PATCH] [ELF] Support discarding .relr.dyn

db08df0570b6dfaf00d7b1b8555c1d2d4effb224 does not work because part.relrDyn is
a unique_ptr and `reset` destroys the object which may still be referenced.

This commit uses the D114180 approach. Also improve the test to check that there
is no R_X86_64_RELATIVE.
---
 lld/ELF/LinkerScript.cpp                        | 4 +---
 lld/ELF/SyntheticSections.cpp                   | 3 ++-
 lld/test/ELF/linkerscript/discard-section-err.s | 2 ++
 3 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/lld/ELF/LinkerScript.cpp b/lld/ELF/LinkerScript.cpp
index 8870db771fa7..00a5492031bf 100644
--- a/lld/ELF/LinkerScript.cpp
+++ b/lld/ELF/LinkerScript.cpp
@@ -564,15 +564,13 @@ void LinkerScript::discard(InputSectionBase &s) {
   if (&s == in.shStrTab.get())
     error("discarding " + s.name + " section is not allowed");
 
-  // You can discard .hash, .gnu.hash, and .relr.dyn sections by linker scripts.
+  // You can discard .hash and .gnu.hash sections by linker scripts.
   // Since they are synthesized sections, we need to handle them differently
   // than other regular sections.
   if (&s == mainPart->gnuHashTab)
     mainPart->gnuHashTab = nullptr;
   else if (&s == mainPart->hashTab)
     mainPart->hashTab = nullptr;
-  else if (&s == mainPart->relrDyn.get())
-    mainPart->relrDyn.reset();
 
   s.markDead();
   s.parent = nullptr;
diff --git a/lld/ELF/SyntheticSections.cpp b/lld/ELF/SyntheticSections.cpp
index d0f3c87ac8c7..680281f3315e 100644
--- a/lld/ELF/SyntheticSections.cpp
+++ b/lld/ELF/SyntheticSections.cpp
@@ -1412,7 +1412,8 @@ DynamicSection<ELFT>::computeContents() {
         addInt(isRela ? DT_RELACOUNT : DT_RELCOUNT, numRelativeRels);
     }
   }
-  if (part.relrDyn && !part.relrDyn->relocs.empty()) {
+  if (part.relrDyn && part.relrDyn->getParent() &&
+      !part.relrDyn->relocs.empty()) {
     addInSec(config->useAndroidRelrTags ? DT_ANDROID_RELR : DT_RELR,
              *part.relrDyn);
     addInt(config->useAndroidRelrTags ? DT_ANDROID_RELRSZ : DT_RELRSZ,
diff --git a/lld/test/ELF/linkerscript/discard-section-err.s b/lld/test/ELF/linkerscript/discard-section-err.s
index c186ba00af41..592c33fdd5cc 100644
--- a/lld/test/ELF/linkerscript/discard-section-err.s
+++ b/lld/test/ELF/linkerscript/discard-section-err.s
@@ -27,6 +27,8 @@
 # RUN: llvm-readobj -S %t | FileCheck /dev/null --implicit-check-not='Name: .rela.dyn'
 
 # RUN: echo "SECTIONS { /DISCARD/ : { *(.relr.dyn) } }" > %t.script
+# RUN: ld.lld -pie --pack-dyn-relocs=relr -T %t.script %t.o -o %t
+# RUN: llvm-readobj -S -r %t | FileCheck /dev/null --implicit-check-not='Name: .relr.dyn' --implicit-check-not=R_X86_64_RELATIVE
 
 .data
 .align 8