[ELF] - Implement -z nodefaultlib

[grimar]

Summary

This is https://bugs.llvm.org//show_bug.cgi?id=38978.

Spec says that:

Objects may be built with the -z nodefaultlib option to suppress any search of the default locations at runtime.
Use of this option implies that all the dependencies of an object can be located using its runpaths.
Without this option, which is the most common case, no matter how you augment the runtime linker's library
search path, its last element is always /usr/lib for 32-bit objects and /usr/lib/64 for 64-bit objects.

(https://www.shrubbery.net/solaris9ab/SUNWdev/LLM/p4.html#CHAPTER2-84569)

The patch implements this option.

[grimar]

Ping.

[emaste]

docs/ld.lld.1

501

looks like the rest of this sentence is missing - e.g.
Set the DF_1_NODEFLIB flag to ...

[grimar]

• Addressed review comment.

docs/ld.lld.1

501

Thanks!

[ruiu]

LGTM

docs/ld.lld.1

502

path -> paths

ELF/Config.h

struct Configuration {
   bool ZCombreloc;
   bool ZCopyreloc;
   bool ZExecstack;
   bool ZGlobal;
   bool ZHazardplt;
   bool ZInitfirst;
   bool ZInterpose;
   bool ZKeepTextSectionPrefix;
+  bool ZNodefaultlib;
   bool ZNodelete;
   bool ZNodlopen;
   bool ZNow;
   bool ZOrigin;
   bool ZRelro;
   bool ZRodynamic;
   bool ZText;
   bool ZRetpolineplt;

ELF/Driver.cpp

static bool getZFlag(opt::InputArgList &Args, StringRef K1, StringRef K2,
   return Default;
 }
 
 static bool isKnownZFlag(StringRef S) {
   return S == "combreloc" || S == "copyreloc" || S == "defs" ||
          S == "execstack" || S == "global" || S == "hazardplt" ||
          S == "initfirst" || S == "interpose" ||
          S == "keep-text-section-prefix" || S == "lazy" || S == "muldefs" ||
-         S == "nocombreloc" || S == "nocopyreloc" || S == "nodelete" ||
-         S == "nodlopen" || S == "noexecstack" ||
+         S == "nocombreloc" || S == "nocopyreloc" || S == "nodefaultlib" ||
+         S == "nodelete" || S == "nodlopen" || S == "noexecstack" ||
          S == "nokeep-text-section-prefix" || S == "norelro" || S == "notext" ||
          S == "now" || S == "origin" || S == "relro" || S == "retpolineplt" ||
          S == "rodynamic" || S == "text" || S == "wxneeded" ||
          S.startswith("max-page-size=") || S.startswith("stack-size=");
 }
 
 // Report an error for an unknown -z option.
 static void checkZOptions(opt::InputArgList &Args) {
void LinkerDriver::readConfigs(opt::InputArgList &Args) {
   Config->ZCopyreloc = getZFlag(Args, "copyreloc", "nocopyreloc", true);
   Config->ZExecstack = getZFlag(Args, "execstack", "noexecstack", false);
   Config->ZGlobal = hasZOption(Args, "global");
   Config->ZHazardplt = hasZOption(Args, "hazardplt");
   Config->ZInitfirst = hasZOption(Args, "initfirst");
   Config->ZInterpose = hasZOption(Args, "interpose");
   Config->ZKeepTextSectionPrefix = getZFlag(
       Args, "keep-text-section-prefix", "nokeep-text-section-prefix", false);
+  Config->ZNodefaultlib = hasZOption(Args, "nodefaultlib");
   Config->ZNodelete = hasZOption(Args, "nodelete");
   Config->ZNodlopen = hasZOption(Args, "nodlopen");
   Config->ZNow = getZFlag(Args, "now", "lazy", false);
   Config->ZOrigin = hasZOption(Args, "origin");
   Config->ZRelro = getZFlag(Args, "relro", "norelro", true);
   Config->ZRetpolineplt = hasZOption(Args, "retpolineplt");
   Config->ZRodynamic = hasZOption(Args, "rodynamic");
   Config->ZStackSize = args::getZOptionValue(Args, OPT_z, "stack-size", 0);

ELF/SyntheticSections.cpp

template <class ELFT> void DynamicSection<ELFT>::finalizeContents() {
   if (Config->Bsymbolic)
     DtFlags |= DF_SYMBOLIC;
   if (Config->ZGlobal)
     DtFlags1 |= DF_1_GLOBAL;
   if (Config->ZInitfirst)
     DtFlags1 |= DF_1_INITFIRST;
   if (Config->ZInterpose)
     DtFlags1 |= DF_1_INTERPOSE;
+  if (Config->ZNodefaultlib)
+    DtFlags1 |= DF_1_NODEFLIB;
   if (Config->ZNodelete)
     DtFlags1 |= DF_1_NODELETE;
   if (Config->ZNodlopen)
     DtFlags1 |= DF_1_NOOPEN;
   if (Config->ZNow) {
     DtFlags |= DF_BIND_NOW;
     DtFlags1 |= DF_1_NOW;
   }

docs/ld.lld.1

 Do not error if a symbol is defined multiple times.
 The first definition will be used.
 This is a synonym for
 .Fl -allow-multiple-definition.
 .It Cm nocombreloc
 Disable combining and sorting multiple relocation sections.
 .It Cm nocopyreloc
 Disable the creation of copy relocations.
+.It Cm nodefaultlib
+Set the
+.Dv DF_1_NODEFLIB
+flag to indicate that default library search path should be ignored.
 .It Cm nodelete
 Set the
 .Dv DF_1_NODELETE
 flag to indicate that the object cannot be unloaded from a process.
 .It Cm nodlopen
 Set the
 .Dv DF_1_NOOPEN
 flag to indcate that the object may not be opened by

test/ELF/dt_flags.s

 # REQUIRES: x86
 
 # RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t
 # RUN: ld.lld -shared %t -o %t.so
 
-# RUN: ld.lld -z global -z initfirst -z interpose -z now -z nodelete \
-# RUN:   -z nodlopen -z origin -Bsymbolic %t %t.so -o %t1
+# RUN: ld.lld -z global -z initfirst -z interpose -z now -z nodefaultlib \
+# RUN:   -z nodelete -z nodlopen -z origin -Bsymbolic %t %t.so -o %t1
 # RUN: llvm-readobj -dynamic-table %t1 | FileCheck -check-prefix=FLAGS %s
 
 # RUN: ld.lld %t %t.so -o %t2
 # RUN: llvm-readobj -dynamic-table %t2 | FileCheck %s
 
 # RUN: ld.lld -z lazy %t %t.so -o %t2
 # RUN: llvm-readobj -dynamic-table %t2 | FileCheck %s
 
 # FLAGS: DynamicSection [
 # FLAGS:   0x000000000000001E FLAGS ORIGIN SYMBOLIC BIND_NOW
-# FLAGS:   0x000000006FFFFFFB FLAGS_1 NOW GLOBAL NODELETE INITFIRST NOOPEN ORIGIN INTERPOSE
+# FLAGS:   0x000000006FFFFFFB FLAGS_1 NOW GLOBAL NODELETE INITFIRST NOOPEN ORIGIN INTERPOSE NODEFLIB
 # FLAGS: ]
 
 # CHECK: DynamicSection [
 # CHECK-NOT:   FLAGS
 # CHECK-NOT:   FLAGS_1
 # CHECK: ]
 
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