1 files changed, 62 insertions, 8 deletions

diff --git a/lld/ELF/Driver.cpp b/lld/ELF/Driver.cpp
index 342e70953fb..98650a74b4e 100644
--- a/lld/ELF/Driver.cpp
+++ b/lld/ELF/Driver.cpp
@@ -51,6 +51,7 @@
 #include "llvm/ADT/StringSwitch.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/Compression.h"
+#include "llvm/Support/LEB128.h"
 #include "llvm/Support/Path.h"
 #include "llvm/Support/TarWriter.h"
 #include "llvm/Support/TargetSelect.h"
@@ -296,7 +297,7 @@ static void checkOptions(opt::InputArgList &Args) {
       error("-r and --gc-sections may not be used together");
     if (Config->GdbIndex)
       error("-r and --gdb-index may not be used together");
-    if (Config->ICF)
+    if (Config->ICF != ICFLevel::None)
       error("-r and --icf may not be used together");
     if (Config->Pie)
       error("-r and -pie may not be used together");
@@ -519,6 +520,15 @@ static StringRef getDynamicLinker(opt::InputArgList &Args) {
   return Arg->getValue();
 }
 
+static ICFLevel getICF(opt::InputArgList &Args) {
+  auto *Arg = Args.getLastArg(OPT_icf_none, OPT_icf_safe, OPT_icf_all);
+  if (!Arg || Arg->getOption().getID() == OPT_icf_none)
+    return ICFLevel::None;
+  if (Arg->getOption().getID() == OPT_icf_safe)
+    return ICFLevel::Safe;
+  return ICFLevel::All;
+}
+
 static StripPolicy getStrip(opt::InputArgList &Args) {
   if (Args.hasArg(OPT_relocatable))
     return StripPolicy::None;
@@ -745,7 +755,7 @@ void LinkerDriver::readConfigs(opt::InputArgList &Args) {
   Config->GcSections = Args.hasFlag(OPT_gc_sections, OPT_no_gc_sections, false);
   Config->GnuUnique = Args.hasFlag(OPT_gnu_unique, OPT_no_gnu_unique, true);
   Config->GdbIndex = Args.hasFlag(OPT_gdb_index, OPT_no_gdb_index, false);
-  Config->ICF = Args.hasFlag(OPT_icf_all, OPT_icf_none, false);
+  Config->ICF = getICF(Args);
   Config->IgnoreDataAddressEquality =
       Args.hasArg(OPT_ignore_data_address_equality);
   Config->IgnoreFunctionAddressEquality =
@@ -1225,16 +1235,60 @@ template <class ELFT> static void demoteSymbols() {
   }
 }
 
+static bool keepUnique(Symbol *S) {
+  if (auto *D = dyn_cast_or_null<Defined>(S)) {
+    if (D->Section) {
+      D->Section->KeepUnique = true;
+      return true;
+    }
+  }
+  return false;
+}
+
 // Record sections that define symbols mentioned in --keep-unique <symbol>
-// these sections are inelligible for ICF.
+// and symbols referred to by address-significance tables. These sections are
+// ineligible for ICF.
+template <class ELFT>
 static void findKeepUniqueSections(opt::InputArgList &Args) {
   for (auto *Arg : Args.filtered(OPT_keep_unique)) {
     StringRef Name = Arg->getValue();
-    if (auto *Sym = dyn_cast_or_null<Defined>(Symtab->find(Name)))
-      Sym->Section->KeepUnique = true;
-    else
+    if (!keepUnique(Symtab->find(Name)))
       warn("could not find symbol " + Name + " to keep unique");
   }
+
+  if (Config->ICF == ICFLevel::Safe) {
+    // Symbols in the dynsym could be address-significant in other executables
+    // or DSOs, so we conservatively mark them as address-significant.
+    for (Symbol *S : Symtab->getSymbols())
+      if (S->includeInDynsym())
+        keepUnique(S);
+
+    // Visit the address-significance table in each object file and mark each
+    // referenced symbol as address-significant.
+    for (InputFile *F : ObjectFiles) {
+      auto *Obj = cast<ObjFile<ELFT>>(F);
+      ArrayRef<Symbol *> Syms = Obj->getSymbols();
+      if (Obj->AddrsigSec) {
+        ArrayRef<uint8_t> Contents =
+            check(Obj->getObj().getSectionContents(Obj->AddrsigSec));
+        const uint8_t *Cur = Contents.begin();
+        while (Cur != Contents.end()) {
+          unsigned Size;
+          const char *Err;
+          uint64_t SymIndex = decodeULEB128(Cur, &Size, Contents.end(), &Err);
+          if (Err)
+            fatal(toString(F) + ": could not decode addrsig section: " + Err);
+          keepUnique(Syms[SymIndex]);
+          Cur += Size;
+        }
+      } else {
+        // If an object file does not have an address-significance table,
+        // conservatively mark all of its symbols as address-significant.
+        for (Symbol *S : Syms)
+          keepUnique(S);
+      }
+    }
+  }
 }
 
 // Do actual linking. Note that when this function is called,
@@ -1409,8 +1463,8 @@ template <class ELFT> void LinkerDriver::link(opt::InputArgList &Args) {
   markLive<ELFT>();
   demoteSymbols<ELFT>();
   mergeSections();
-  if (Config->ICF) {
-    findKeepUniqueSections(Args);
+  if (Config->ICF != ICFLevel::None) {
+    findKeepUniqueSections<ELFT>(Args);
     doIcf<ELFT>();
   }