[ELF] Make foo@@v1 resolve undefined foo@v1

The symbol resolution rules for versioned symbols are:

* foo@@v1 (default version) resolves both undefined foo and foo@v1
* foo@v1 (non-default version) resolves undefined foo@v1

Note, foo@@v1 must be defined (the assembler errors if attempting to
create an undefined foo@@v1).

For defined foo@@v1 in a shared object, we call `SymbolTable::addSymbol` twice,
one for foo and the other for foo@v1. We don't do the same for object files, so
foo@@v1 defined in one object file incorrectly does not resolve a foo@v1
reference in another object file.

This patch fixes the issue by reusing the --wrap code to redirect symbols in
object files. This has to be done after processing input files because
foo and foo@v1 are two separate symbols if we haven't seen foo@@v1.

Add a helper `Symbol::getVersionSuffix` to retrieve the optional trailing
`@...` or `@@...` from the possibly truncated symbol name.

Depends on D92258

Reviewed By: jhenderson

Differential Revision: https://reviews.llvm.org/D92259

lld/ELF/Driver.cpp

@@ -1919,17 +1919,46 @@ static std::vector<WrappedSymbol> addWrappedSymbols(opt::InputArgList &args) {
   return v;
 }
 
-// Do renaming for -wrap by updating pointers to symbols.
+// Do renaming for -wrap and foo@v1 by updating pointers to symbols.
 //
 // When this function is executed, only InputFiles and symbol table
 // contain pointers to symbol objects. We visit them to replace pointers,
 // so that wrapped symbols are swapped as instructed by the command line.
-static void wrapSymbols(ArrayRef<WrappedSymbol> wrapped) {
+static void redirectSymbols(ArrayRef<WrappedSymbol> wrapped) {
+  llvm::TimeTraceScope timeScope("Redirect symbols");
   DenseMap<Symbol *, Symbol *> map;
   for (const WrappedSymbol &w : wrapped) {
     map[w.sym] = w.wrap;
     map[w.real] = w.sym;
   }
+  for (Symbol *sym : symtab->symbols()) {
+    // Enumerate symbols with a non-default version (foo@v1).
+    StringRef name = sym->getName();
+    const char *suffix1 = sym->getVersionSuffix();
+    if (suffix1[0] != '@' || suffix1[1] == '@')
+      continue;
+
+    // Check whether the default version foo@@v1 exists. If it exists, the
+    // symbol can be found by the name "foo" in the symbol table.
+    Symbol *maybeDefault = symtab->find(name);
+    if (!maybeDefault)
+      continue;
+    const char *suffix2 = maybeDefault->getVersionSuffix();
+    if (suffix2[0] != '@' || suffix2[1] != '@' ||
+        strcmp(suffix1 + 1, suffix2 + 2) != 0)
+      continue;
+
+    // foo@v1 and foo@@v1 should be merged, so redirect foo@v1 to foo@@v1.
+    map.try_emplace(sym, maybeDefault);
+    // If both foo@v1 and foo@@v1 are defined and non-weak, report a duplicate
+    // definition error.
+    maybeDefault->resolve(*sym);
+    // Eliminate foo@v1 from the symbol table.
+    sym->symbolKind = Symbol::PlaceholderKind;
+  }
+
+  if (map.empty())
+    return;
 
   // Update pointers in input files.
   parallelForEach(objectFiles, [&](InputFile *file) {
@@ -2158,9 +2187,8 @@ template <class ELFT> void LinkerDriver::link(opt::InputArgList &args) {
       !config->thinLTOModulesToCompile.empty())
     return;
 
-  // Apply symbol renames for -wrap.
-  if (!wrapped.empty())
-    wrapSymbols(wrapped);
+  // Apply symbol renames for -wrap and combine foo@v1 and foo@@v1.
+  redirectSymbols(wrapped);
 
   {
     llvm::TimeTraceScope timeScope("Aggregate sections");

lld/ELF/Symbols.cpp

@@ -37,11 +37,9 @@ std::string lld::toString(const elf::Symbol &sym) {
   StringRef name = sym.getName();
   std::string ret = demangle(name);
 
-  // If sym has a non-default version, its name may have been truncated at '@'
-  // by Symbol::parseSymbolVersion(). Add the trailing part. This check is safe
-  // because every symbol name ends with '\0'.
-  if (name.data()[name.size()] == '@')
-    ret += name.data() + name.size();
+  const char *suffix = sym.getVersionSuffix();
+  if (*suffix == '@')
+    ret += suffix;
   return ret;
 }
 

lld/ELF/Symbols.h

@@ -178,6 +178,15 @@ public:
 
   void parseSymbolVersion();
 
+  // Get the NUL-terminated version suffix ("", "@...", or "@@...").
+  //
+  // For @@, the name has been truncated by insert(). For @, the name has been
+  // truncated by Symbol::parseSymbolVersion().
+  const char *getVersionSuffix() const {
+    assert(nameSize != (uint32_t)-1);
+    return nameData + nameSize;
+  }
+
   bool isInGot() const { return gotIndex != -1U; }
   bool isInPlt() const { return pltIndex != -1U; }
 

lld/test/ELF/symver.s

@@ -15,29 +15,33 @@
 # RUN: ld.lld -shared --soname=def1.so --version-script=%t/ver %t/def1.o -o %t/def1.so
 # RUN: ld.lld -shared --soname=hid1.so --version-script=%t/ver %t/hid1.o -o %t/hid1.so
 
-## TODO Report a duplicate definition error for foo@v1 and foo@@v1.
-# RUN: ld.lld -shared --version-script=%t/ver %t/def1.o %t/hid1.o -o /dev/null
-
+## Report a duplicate definition error for foo@v1 and foo@@v1.
+# RUN: not ld.lld -shared --version-script=%t/ver %t/def1.o %t/hid1.o -o /dev/null 2>&1 | \
+# RUN:   FileCheck %s --check-prefix=DUP
 # RUN: ld.lld -shared --version-script=%t/ver %t/def1w.o %t/hid1.o -o /dev/null
 # RUN: ld.lld -shared --version-script=%t/ver %t/def1.o %t/hid1w.o -o /dev/null
 # RUN: ld.lld -shared --version-script=%t/ver %t/def1w.o %t/hid1w.o -o /dev/null
 
-## TODO foo@@v1 should resolve undefined foo@v1.
-# RUN: not ld.lld -shared --version-script=%t/ver %t/ref1p.o %t/def1.o -o /dev/null
+# DUP:      error: duplicate symbol: foo@@v1
+# DUP-NEXT: >>> defined at {{.*}}/def1{{w?}}.o:(.text+0x0)
+# DUP-NEXT: >>> defined at {{.*}}/hid1.o:(.text+0x0)
+
+## Protected undefined foo@v1 makes the output symbol protected.
+# RUN: ld.lld -shared --version-script=%t/ver %t/ref1p.o %t/def1.o -o %t.protected
+# RUN: llvm-readelf --dyn-syms %t.protected | FileCheck %s --check-prefix=PROTECTED
+
+# PROTECTED:  NOTYPE GLOBAL PROTECTED [[#]] foo@@v1
 
-## TODO
 ## foo@@v1 resolves both undefined foo and foo@v1. There is one single definition.
 ## Note: set soname so that the name string referenced by .gnu.version_d is fixed.
 # RUN: ld.lld -shared --soname=t --version-script=%t/ver %t/ref.o %t/ref1.o %t/def1.o -o %t1
 # RUN: llvm-readelf -r --dyn-syms %t1 | FileCheck %s
 
-# CHECK:       Relocation section '.rela.plt' at offset {{.*}} contains 2 entries:
+# CHECK:       Relocation section '.rela.plt' at offset {{.*}} contains 1 entries:
 # CHECK-NEXT:  {{.*}} Type               {{.*}}
 # CHECK-NEXT:  {{.*}} R_X86_64_JUMP_SLOT {{.*}} foo@@v1 + 0
-# CHECK-NEXT:  {{.*}} R_X86_64_JUMP_SLOT {{.*}} foo + 0
 
-# CHECK:       1: {{.*}} NOTYPE GLOBAL DEFAULT UND   foo{{$}}
-# CHECK-NEXT:  2: {{.*}} NOTYPE GLOBAL DEFAULT [[#]] foo@@v1
+# CHECK:       1: {{.*}} NOTYPE GLOBAL DEFAULT [[#]] foo@@v1
 # CHECK-EMPTY:
 
 ## foo@@v2 does not resolve undefined foo@v1.
@@ -96,10 +100,9 @@
 # RUN: llvm-readobj -r %t.w1 | FileCheck %s --check-prefix=W1REL
 # RUN: llvm-objdump -d --no-show-raw-insn %t.w1 | FileCheck %s --check-prefix=W1DIS
 
-## TODO foo should be foo@@v1.
 # W1REL:      .rela.plt {
 # W1REL-NEXT:   R_X86_64_JUMP_SLOT __wrap_foo 0x0
-# W1REL-NEXT:   R_X86_64_JUMP_SLOT foo 0x0
+# W1REL-NEXT:   R_X86_64_JUMP_SLOT foo@@v1 0x0
 # W1REL-NEXT: }
 
 # W1DIS-LABEL: <.text>:
@@ -150,7 +153,6 @@
 # W4DIS-COUNT-3: int3
 # W4DIS-NEXT:    callq {{.*}} <__wrap_foo@plt>
 
-## TODO The two callq should jump to the same address.
 ## Note: GNU ld errors "no symbol version section for versioned symbol `__wrap_foo@@v1'".
 # RUN: ld.lld -shared --soname=t --version-script=%t/ver --wrap=foo@@v1 %t/ref.o %t/ref1.o %t/def1.o %t/wrap.o -o %t.w5
 # RUN: llvm-readobj -r %t.w5 | FileCheck %s --check-prefix=W5REL
@@ -158,13 +160,12 @@
 
 # W5REL:      .rela.plt {
 # W5REL-NEXT:   R_X86_64_JUMP_SLOT foo@@v1 0x0
-# W5REL-NEXT:   R_X86_64_JUMP_SLOT foo 0x0
 # W5REL-NEXT: }
 
 # W5DIS-LABEL: <.text>:
-# W5DIS-NEXT:    callq 0x1380 <foo@plt>
+# W5DIS-NEXT:    callq 0x1350 <foo@plt>
 # W5DIS-COUNT-3: int3
-# W5DIS-NEXT:    callq 0x1390 <foo@plt>
+# W5DIS-NEXT:    callq 0x1350 <foo@plt>
 
 #--- ver
 v1 {};