lld: add -z interpose support

emaste · emaste · commit c0b474f67a33 · 2018-09-14T14:25:37.000Z
-z interpose sets the DF_1_INTERPOSE flag, marking the object as an interposer. Via FreeBSD PR 230604, linking Valgrind with lld failed. Differential Revision: https://reviews.llvm.org/D52094 llvm-svn: 342239
diff --git a/lld/ELF/Config.h b/lld/ELF/Config.h
@@ -184,6 +184,7 @@ struct Configuration {
   bool ZGlobal;
   bool ZHazardplt;
   bool ZInitfirst;
+  bool ZInterpose;
   bool ZKeepTextSectionPrefix;
   bool ZNodelete;
   bool ZNodlopen;
diff --git a/lld/ELF/Driver.cpp b/lld/ELF/Driver.cpp
@@ -341,9 +341,10 @@ static bool getZFlag(opt::InputArgList &Args, StringRef K1, StringRef K2,
 static bool isKnown(StringRef S) {
   return S == "combreloc" || S == "copyreloc" || S == "defs" ||
          S == "execstack" || S == "global" || S == "hazardplt" ||
-         S == "initfirst" || S == "keep-text-section-prefix" || S == "lazy" ||
-         S == "muldefs" || S == "nocombreloc" || S == "nocopyreloc" ||
-         S == "nodelete" || S == "nodlopen" || S == "noexecstack" ||
+         S == "initfirst" || S == "interpose" ||
+         S == "keep-text-section-prefix" || S == "lazy" || S == "muldefs" ||
+         S == "nocombreloc" || S == "nocopyreloc" || 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" ||
@@ -836,6 +837,7 @@ void LinkerDriver::readConfigs(opt::InputArgList &Args) {
   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->ZNodelete = hasZOption(Args, "nodelete");
diff --git a/lld/ELF/SyntheticSections.cpp b/lld/ELF/SyntheticSections.cpp
@@ -1268,6 +1268,8 @@ template <class ELFT> void DynamicSection<ELFT>::finalizeContents() {
     DtFlags1 |= DF_1_GLOBAL;
   if (Config->ZInitfirst)
     DtFlags1 |= DF_1_INITFIRST;
+  if (Config->ZInterpose)
+    DtFlags1 |= DF_1_INTERPOSE;
   if (Config->ZNodelete)
     DtFlags1 |= DF_1_NODELETE;
   if (Config->ZNodlopen)
diff --git a/lld/docs/ld.lld.1 b/lld/docs/ld.lld.1
@@ -3,7 +3,7 @@
 .\"
 .\" This man page documents only lld's ELF linking support, obtained originally
 .\" from FreeBSD.
-.Dd July 30, 2018
+.Dd September 14, 2018
 .Dt LD.LLD 1
 .Os
 .Sh NAME
@@ -446,6 +446,12 @@ segment.
 Sets the
 .Dv DF_1_INITFIRST
 flag to indicate the module should be initialized first.
+.It Cm interpose
+Set the
+.Dv DF_1_INTERPOSE
+flag to indicate to the runtime linker that the object is an interposer.
+During symbol resolution interposers are searched after the application
+but before other dependencies.
 .It Cm muldefs
 Do not error if a symbol is defined multiple times.
 The first definition will be used.
diff --git a/lld/test/ELF/dt_flags.s b/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 now -z nodelete -z nodlopen -z origin \
-# RUN:   -Bsymbolic %t %t.so -o %t1
+# 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: 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
+# FLAGS:   0x000000006FFFFFFB FLAGS_1 NOW GLOBAL NODELETE INITFIRST NOOPEN ORIGIN INTERPOSE
 # FLAGS: ]
 
 # CHECK: DynamicSection [
