[ELF] Don't set versionId on undefined weak lazy symbols

An unfetched lazy symbol (undefined weak) should be considered to have its
original versionId which is VER_NDX_GLOBAL, instead of the lazy symbol's
versionId. (The original versionId cannot be non-VER_NDX_GLOBAL because a
undefined versioned symbol is an error.)

The regression was introduced in D77280 when making version scripts work
with lazy symbols fetched by LTO calls.

Fix PR49915

Differential Revision: https://reviews.llvm.org/D100624

lld/ELF/SyntheticSections.cpp

@@ -3123,7 +3123,9 @@ size_t VersionTableSection::getSize() const {
 void VersionTableSection::writeTo(uint8_t *buf) {
   buf += 2;
   for (const SymbolTableEntry &s : getPartition().dynSymTab->getSymbols()) {
-    write16(buf, s.sym->versionId);
+    // Use the original versionId for an unfetched lazy symbol (undefined weak),
+    // which must be VER_NDX_GLOBAL (an undefined versioned symbol is an error).
+    write16(buf, s.sym->isLazy() ? VER_NDX_GLOBAL : s.sym->versionId);
     buf += 2;
   }
 }

lld/test/ELF/version-script-weak.s

@@ -24,6 +24,19 @@
 # CHECK-NEXT:   Section: Undefined
 # CHECK-NEXT: }
 
+## The version of an unfetched lazy symbol is VER_NDX_GLOBAL. It is not affected by version scripts.
+# RUN: echo "v1 { *; };" > %t2.script
+# RUN: ld.lld -shared --version-script %t2.script %t.o --start-lib %t1.o --end-lib -o %t2.so
+# RUN: llvm-readelf --dyn-syms %t2.so | FileCheck %s --check-prefix=CHECK2
+
+# CHECK2: NOTYPE WEAK DEFAULT UND foo{{$}}
+
+# RUN: ld.lld -shared --soname=tshared --version-script %t2.script %t1.o -o %tshared.so
+# RUN: ld.lld -shared --version-script %t2.script %t.o --start-lib %t1.o --end-lib %tshared.so -o %t3.so
+# RUN: llvm-readelf --dyn-syms %t3.so | FileCheck %s --check-prefix=CHECK3
+
+# CHECK3: NOTYPE WEAK DEFAULT UND foo@v1
+
 .text
  callq foo@PLT
 .weak foo