[PATCH] D23502: [ELF] Linkerscript: discard .interp section if we have custom PHDRS layout and PT_INTERP is not listed.

[Eugene Leviant via llvm-commits]

evgeny777 created this revision.
evgeny777 added a reviewer: ruiu.
evgeny777 added subscribers: grimar, ikudrin, llvm-commits.
evgeny777 set the repository for this revision to rL LLVM.
evgeny777 added a project: lld.

Current version may allocate new PT_LOAD in this case, which wastes space in ELF image and breaks our product linking.

Repository:
  rL LLVM

https://reviews.llvm.org/D23502

Files:
  ELF/LinkerScript.cpp
  ELF/LinkerScript.h
  ELF/Writer.cpp
  test/ELF/linkerscript/linkerscript-discard-interp.s

Index: test/ELF/linkerscript/linkerscript-discard-interp.s
===================================================================
--- test/ELF/linkerscript/linkerscript-discard-interp.s
+++ test/ELF/linkerscript/linkerscript-discard-interp.s
@@ -0,0 +1,12 @@
+// RUN: llvm-mc -filetype=obj -triple=i686-unknown-linux %s -o %t.o
+// RUN: llvm-mc -filetype=obj -triple=i686-unknown-linux %p/../Inputs/shared.s -o %t2.o
+// RUN: ld.lld -shared %t2.o -o %t2.so
+// RUN: echo "PHDRS { text PT_LOAD FILEHDR PHDRS; } \
+// RUN:       SECTIONS { .text : { *(.text) } : text }" >> %t.script
+// RUN: ld.lld -dynamic-linker /lib64/ld-linux-x86-64.so.2 -rpath foo -rpath bar --script %t.script --export-dynamic %t.o %t2.so -o %t
+// RUN: llvm-readobj -s %t | FileCheck %s
+
+// CHECK-NOT:        Name: .interp
+
+.global _start
+_start:
Index: ELF/Writer.cpp
===================================================================
--- ELF/Writer.cpp
+++ ELF/Writer.cpp
@@ -105,7 +105,8 @@
 
 template <class ELFT> static bool needsInterpSection() {
   return !Symtab<ELFT>::X->getSharedFiles().empty() &&
-         !Config->DynamicLinker.empty();
+         !Config->DynamicLinker.empty() &&
+         !Script<ELFT>::X->discardInterpSection();
 }
 
 template <class ELFT> void elf::writeResult() {
Index: ELF/LinkerScript.h
===================================================================
--- ELF/LinkerScript.h
+++ ELF/LinkerScript.h
@@ -144,6 +144,7 @@
   void createSections(OutputSectionFactory<ELFT> &Factory);
 
   std::vector<PhdrEntry<ELFT>> createPhdrs();
+  bool discardInterpSection();
 
   ArrayRef<uint8_t> getFiller(StringRef Name);
   bool shouldKeep(InputSectionBase<ELFT> *S);
Index: ELF/LinkerScript.cpp
===================================================================
--- ELF/LinkerScript.cpp
+++ ELF/LinkerScript.cpp
@@ -486,6 +486,15 @@
   return Ret;
 }
 
+template <class ELFT> bool LinkerScript<ELFT>::discardInterpSection() {
+  // Discard .interp section in case we have PHDRS specification
+  // and PT_INTERP isn't listed.
+  return !Opt.PhdrsCommands.empty() &&
+         llvm::find_if(Opt.PhdrsCommands, [](const PhdrsCommand &Cmd) {
+           return Cmd.Type == PT_INTERP;
+         }) == Opt.PhdrsCommands.end();
+}
+
 template <class ELFT>
 ArrayRef<uint8_t> LinkerScript<ELFT>::getFiller(StringRef Name) {
   for (const std::unique_ptr<BaseCommand> &Base : Opt.Commands)


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