[ELF] - Implement -z nodefaultlib

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."

The patch implements this option.

Differential revision: https://reviews.llvm.org/D54577

llvm-svn: 347647

lld/ELF/Config.h

@@ -189,6 +189,7 @@ struct Configuration {
   bool ZInitfirst;
   bool ZInterpose;
   bool ZKeepTextSectionPrefix;
+  bool ZNodefaultlib;
   bool ZNodelete;
   bool ZNodlopen;
   bool ZNow;

lld/ELF/Driver.cpp

@@ -350,8 +350,8 @@ static bool isKnownZFlag(StringRef S) {
          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" ||
@@ -876,6 +876,7 @@ void LinkerDriver::readConfigs(opt::InputArgList &Args) {
   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);

lld/ELF/SyntheticSections.cpp

@@ -1268,6 +1268,8 @@ template <class ELFT> void DynamicSection<ELFT>::finalizeContents() {
     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)

lld/docs/ld.lld.1

@@ -496,6 +496,10 @@ This is a synonym for
 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 paths should be ignored.
 .It Cm nodelete
 Set the
 .Dv DF_1_NODELETE

lld/test/ELF/dt_flags.s

@@ -3,8 +3,8 @@
 # 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
@@ -15,7 +15,7 @@
 
 # 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 [