[ELF] PROVIDE: fix spurious "symbol not found"

When archive member extraction involving ENTRY happens after
`addScriptReferencedSymbolsToSymTable`,
`addScriptReferencedSymbolsToSymTable` may fail to define some PROVIDE
symbols used by ENTRY. This is an edge case that regressed after llvm#84512.
(The interaction with PROVIDE and ENTRY-in-archive was not considered
before).

Fixes: ebb326a

Author: MaskRay

lld/ELF/Driver.cpp

@@ -2727,13 +2727,6 @@ template <class ELFT> void LinkerDriver::link(opt::InputArgList &args) {
   // Create dynamic sections for dynamic linking and static PIE.
   config->hasDynSymTab = !ctx.sharedFiles.empty() || config->isPic;
 
-  script->addScriptReferencedSymbolsToSymTable();
-
-  // Prevent LTO from removing any definition referenced by -u.
-  for (StringRef name : config->undefined)
-    if (Defined *sym = dyn_cast_or_null<Defined>(symtab.find(name)))
-      sym->isUsedInRegularObj = true;
-
   // If an entry symbol is in a static archive, pull out that file now.
   if (Symbol *sym = symtab.find(config->entry))
     handleUndefined(sym, "--entry");
@@ -2742,6 +2735,16 @@ template <class ELFT> void LinkerDriver::link(opt::InputArgList &args) {
   for (StringRef pat : args::getStrings(args, OPT_undefined_glob))
     handleUndefinedGlob(pat);
 
+  // After potential archive member extraction involving ENTRY and
+  // -u/--undefined-glob, check whether PROVIDE symbols should be defined (the
+  // RHS may refer to definitions in just extracted object files).
+  script->addScriptReferencedSymbolsToSymTable();
+
+  // Prevent LTO from removing any definition referenced by -u.
+  for (StringRef name : config->undefined)
+    if (Defined *sym = dyn_cast_or_null<Defined>(symtab.find(name)))
+      sym->isUsedInRegularObj = true;
+
   // Mark -init and -fini symbols so that the LTO doesn't eliminate them.
   if (Symbol *sym = dyn_cast_or_null<Defined>(symtab.find(config->init)))
     sym->isUsedInRegularObj = true;

lld/test/ELF/linkerscript/symbolreferenced.s

@@ -50,6 +50,21 @@
 # RUN: not ld.lld -T chain2.t a.o 2>&1 | FileCheck %s --check-prefix=ERR --implicit-check-not=error:
 # ERR-COUNT-3: error: chain2.t:1: symbol not found: undef
 
+## _start in a lazy object file references PROVIDE symbols. We extract _start
+## earlier to avoid spurious "symbol not found" errors.
+# RUN: llvm-mc -filetype=obj -triple=x86_64 undef.s -o undef.o
+# RUN: llvm-mc -filetype=obj -triple=x86_64 start.s -o start.o
+# RUN: ld.lld -T chain2.t undef.o --start-lib start.o --end-lib -o lazy
+# RUN: llvm-nm lazy | FileCheck %s --check-prefix=LAZY
+# RUN: ld.lld -e 0 -T chain2.t --undefined-glob '_start*' undef.o --start-lib start.o --end-lib -o lazy
+# RUN: llvm-nm lazy | FileCheck %s --check-prefix=LAZY
+
+# LAZY:      T _start
+# LAZY-NEXT: t f1
+# LAZY-NEXT: T f2
+# LAZY-NEXT: T newsym
+# LAZY-NEXT: T unde
+
 #--- a.s
 .global _start
 _start:
@@ -89,3 +104,13 @@ PROVIDE(newsym = f1);
 PROVIDE(f2 = undef);
 PROVIDE_HIDDEN(f1 = f2);
 PROVIDE(newsym = f1);
+
+#--- undef.s
+.globl undef
+undef: ret
+
+#--- start.s
+.globl _start
+_start: ret
+.data
+.quad newsym