[ELF] - Do not collect SHT_REL[A] sections unconditionally when --gc-sections and --emit-relocs used together.

This is "Bug 34836 - --gc-sections remove relocations from --emit-relocs",

When --emit-relocs is used, LLD currently always drops SHT_REL[A] sections from
output if --gc-sections is present. Patch fixes the issue.

Differential revision: https://reviews.llvm.org/D38724

llvm-svn: 316418

3 files changed, 19 insertions, 13 deletions

diff --git a/lld/ELF/InputSection.h b/lld/ELF/InputSection.h
index 4453da8394e..e36eb40af19 100644
--- a/lld/ELF/InputSection.h
+++ b/lld/ELF/InputSection.h
@@ -237,8 +237,8 @@ public:
 
   // Mark the piece at a given offset live. Used by GC.
   void markLiveAt(uint64_t Offset) {
-    assert(this->Flags & llvm::ELF::SHF_ALLOC);
-    LiveOffsets.insert(Offset);
+    if (this->Flags & llvm::ELF::SHF_ALLOC)
+      LiveOffsets.insert(Offset);
   }
 
   // Translate an offset in the input section to an offset
diff --git a/lld/ELF/MarkLive.cpp b/lld/ELF/MarkLive.cpp
index 62a0039ef01..05fe3a494c7 100644
--- a/lld/ELF/MarkLive.cpp
+++ b/lld/ELF/MarkLive.cpp
@@ -162,9 +162,9 @@ scanEhFrameSection(EhInputSection &EH,
     scanEhFrameSection<ELFT>(EH, EH.template rels<ELFT>(), Fn);
 }
 
-// We do not garbage-collect two types of sections:
-// 1) Sections used by the loader (.init, .fini, .ctors, .dtors or .jcr)
-// 2) Non-allocatable sections which typically contain debugging information
+// Some sections are used directly by the loader, so they should never be
+// garbage-collected. This function returns true if a given section is such
+// section.
 template <class ELFT> static bool isReserved(InputSectionBase *Sec) {
   switch (Sec->Type) {
   case SHT_FINI_ARRAY:
@@ -173,9 +173,6 @@ template <class ELFT> static bool isReserved(InputSectionBase *Sec) {
   case SHT_PREINIT_ARRAY:
     return true;
   default:
-    if (!(Sec->Flags & SHF_ALLOC))
-      return true;
-
     StringRef S = Sec->Name;
     return S.startswith(".ctors") || S.startswith(".dtors") ||
            S.startswith(".init") || S.startswith(".fini") ||
@@ -198,9 +195,6 @@ template <class ELFT> static void doGcSections() {
     if (Sec == &InputSection::Discarded)
       return;
 
-    // We don't gc non alloc sections.
-    if (!(Sec->Flags & SHF_ALLOC))
-      return;
 
     // Usually, a whole section is marked as live or dead, but in mergeable
     // (splittable) sections, each piece of data has independent liveness bit.
diff --git a/lld/test/ELF/emit-relocs-gc.s b/lld/test/ELF/emit-relocs-gc.s
index 5b8bdfe950b..0741e78ab95 100644
--- a/lld/test/ELF/emit-relocs-gc.s
+++ b/lld/test/ELF/emit-relocs-gc.s
@@ -1,18 +1,30 @@
 # REQUIRES: x86
 # RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t.o
 
-## Show that we emit .rela.bar when GC is disabled.
+## Show that we emit .rela.bar and .rela.text when GC is disabled.
 # RUN: ld.lld --emit-relocs %t.o -o %t
 # RUN: llvm-objdump %t -section-headers | FileCheck %s --check-prefix=NOGC
+# NOGC: .rela.text
 # NOGC: .rela.bar
 
-## GC collects .bar section and we exclude .rela.bar from output.
+## GC collects .bar section and we exclude .rela.bar from output. We keep
+## .rela.text because we keep .text.
 # RUN: ld.lld --gc-sections --emit-relocs --print-gc-sections %t.o -o %t \
 # RUN:   | FileCheck --check-prefix=MSG %s
 # MSG: removing unused section from '.bar' in file
 # MSG: removing unused section from '.rela.bar' in file
 # RUN: llvm-objdump %t -section-headers | FileCheck %s --check-prefix=GC
 # GC-NOT:  rela.bar
+# GC:      rela.text
+# GC-NOT:  rela.bar
 
 .section .bar,"a"
 .quad .bar
+
+.text
+relocs:
+.quad _start
+
+.global _start
+_start:
+ nop