[ELF] --wrap: don't clear sym->isUsedInRegularObj if real->isUsedInRegularObj; set wrap's initial binding to sym's

Fix PR49897: if `__real_foo` has the isUsedInRegularObj bit set, we need to
retain `foo` in .symtab, even if `foo` is undefined. The new behavior will match
GNU ld.

Before the patch, we produced an R_X86_64_JUMP_SLOT relocation referencing the
index 0 undefined symbol, which would be erroed by glibc
(see f96ff3c0f8).

While here, fix another bug: if `__wrap_foo` does not exist, its initial binding
should be `foo`'s.

lld/ELF/Driver.cpp

@@ -1888,8 +1888,9 @@ static Symbol *addUndefined(StringRef name) {
       Undefined{nullptr, name, STB_GLOBAL, STV_DEFAULT, 0});
 }
 
-static Symbol *addUnusedUndefined(StringRef name) {
-  Undefined sym{nullptr, name, STB_GLOBAL, STV_DEFAULT, 0};
+static Symbol *addUnusedUndefined(StringRef name,
+                                  uint8_t binding = STB_GLOBAL) {
+  Undefined sym{nullptr, name, binding, STV_DEFAULT, 0};
   sym.isUsedInRegularObj = false;
   return symtab->addSymbol(sym);
 }
@@ -1953,7 +1954,8 @@ static std::vector<WrappedSymbol> addWrappedSymbols(opt::InputArgList &args) {
       continue;
 
     Symbol *real = addUnusedUndefined(saver.save("__real_" + name));
-    Symbol *wrap = addUnusedUndefined(saver.save("__wrap_" + name));
+    Symbol *wrap =
+        addUnusedUndefined(saver.save("__wrap_" + name), sym->binding);
     v.push_back({sym, real, wrap});
 
     // We want to tell LTO not to inline symbols to be overwritten

lld/ELF/SymbolTable.cpp

@@ -42,7 +42,7 @@ void SymbolTable::wrap(Symbol *sym, Symbol *real, Symbol *wrap) {
 
   if (real->exportDynamic)
     sym->exportDynamic = true;
-  if (sym->isUndefined())
+  if (!real->isUsedInRegularObj && sym->isUndefined())
     sym->isUsedInRegularObj = false;
 
   // Now renaming is complete, and no one refers to real. We drop real from

lld/test/ELF/Inputs/wrap-dynamic-undef.s

@@ -1,2 +0,0 @@
-.global foo
-foo:

lld/test/ELF/wrap-dynamic-undef.s

@@ -1,9 +1,10 @@
 # REQUIRES: x86
-# RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux %s -o %t1.o
-# RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux %p/Inputs/wrap-dynamic-undef.s -o %t2.o
-# RUN: ld.lld %t2.o -o %t2.so -shared
-# RUN: ld.lld %t1.o %t2.so -o %t --wrap foo
-# RUN: llvm-readelf --dyn-syms %t | FileCheck %s
+# RUN: split-file %s %t
+# RUN: llvm-mc -filetype=obj -triple=x86_64 %t/a.s -o %t/a.o
+# RUN: llvm-mc -filetype=obj -triple=x86_64 %t/def.s -o %t/def.o
+# RUN: ld.lld %t/def.o -o %t/def.so -shared --soname=def
+# RUN: ld.lld %t/a.o %t/def.so -o %t1 --wrap foo
+# RUN: llvm-readelf --dyn-syms %t1 | FileCheck %s
 
 # Test that the dynamic relocation uses foo. We used to produce a
 # relocation with __real_foo.
@@ -12,6 +13,29 @@
 # CHECK:      NOTYPE  LOCAL  DEFAULT  UND
 # CHECK-NEXT: NOTYPE  GLOBAL DEFAULT  UND foo
 
+# RUN: llvm-mc -filetype=obj -triple=x86_64 %t/b.s -o %t/b.o
+# RUN: ld.lld -shared --wrap foo %t/b.o -o %t2.so
+# RUN: llvm-readelf --dyn-syms %t2.so | FileCheck %s --check-prefix=SYM2
+
+# SYM2:      Symbol table '.dynsym' contains 4 entries:
+# SYM2:      NOTYPE  LOCAL  DEFAULT   UND
+# SYM2-NEXT: NOTYPE  WEAK   DEFAULT   UND foo
+# SYM2-NEXT: NOTYPE  WEAK   DEFAULT   UND __wrap_foo
+# SYM2-NEXT: NOTYPE  GLOBAL DEFAULT [[#]] _start
+
+#--- a.s
 .global _start
 _start:
 	callq	__real_foo@plt
+
+#--- def.s
+.globl foo
+foo:
+
+#--- b.s
+.weak foo
+.weak __real_foo
+.global _start
+_start:
+  call __real_foo@plt
+  call foo@plt