From f9ecf89b16029d3eaf4ca364f75680e5c74e20fe Mon Sep 17 00:00:00 2001
From: Rui Ueyama <ruiu@cs.stanford.edu>
Date: Thu, 25 Feb 2021 20:26:10 +0900
Subject: [PATCH] wip

---
 main.cc        | 10 ++++++++++
 mold.h         |  3 ++-
 object_file.cc | 18 ++++++++++++++++++
 test/shared.sh | 20 ++++++++++++++++++++
 4 files changed, 50 insertions(+), 1 deletion(-)
 create mode 100755 test/shared.sh

diff --git a/main.cc b/main.cc
index b8d21737..01500883 100644
--- a/main.cc
+++ b/main.cc
@@ -1287,6 +1287,16 @@ int main(int argc, char **argv) {
     });
   }
 
+  // If we are linking a .so file, remaining undefined symbols does
+  // not cause a linker error. Instead, they are treated as if they
+  // were imported symbols.
+  if (config.shared) {
+    Timer t("claim_unresolved_symbols");
+    tbb::parallel_for_each(out::objs, [](ObjectFile *file) {
+      file->claim_unresolved_symbols();
+    });
+  }
+
   // Beyond this point, no new symbols will be added to the result.
 
   // Make sure that all symbols have been resolved.
diff --git a/mold.h b/mold.h
index 1154c9bd..15c2fe0d 100644
--- a/mold.h
+++ b/mold.h
@@ -925,6 +925,7 @@ public:
   void handle_undefined_weak_symbols();
   void resolve_comdat_groups();
   void eliminate_duplicate_comdat_groups();
+  void claim_unresolved_symbols();
   void scan_relocations();
   void convert_common_symbols();
   void compute_symtab();
@@ -1230,7 +1231,7 @@ inline bool Symbol::is_absolute() const {
 }
 
 inline bool Symbol::is_imported() const {
-  return file->is_dso;
+  return file->is_dso || (esym && esym->is_undef() && esym->st_bind != STB_WEAK);
 }
 
 inline u64 Symbol::get_addr() const {
diff --git a/object_file.cc b/object_file.cc
index 7dc86363..880d9147 100644
--- a/object_file.cc
+++ b/object_file.cc
@@ -650,6 +650,24 @@ void ObjectFile::eliminate_duplicate_comdat_groups() {
   }
 }
 
+void ObjectFile::claim_unresolved_symbols() {
+  if (!is_alive)
+    return;
+
+  for (i64 i = first_global; i < symbols.size(); i++) {
+    const ElfSym &esym = elf_syms[i];
+    Symbol &sym = *symbols[i];
+    std::lock_guard lock(sym.mu);
+
+    if (esym.is_undef() && (!sym.esym || sym.esym->is_undef())) {
+      if (sym.file && sym.file->priority < this->priority)
+        continue;
+      sym.file = this;
+      sym.esym = &esym;
+    }
+  }
+}
+
 void ObjectFile::scan_relocations() {
   // Scan relocations against seciton contents
   for (InputSection *isec : sections)
diff --git a/test/shared.sh b/test/shared.sh
new file mode 100755
index 00000000..339cac4f
--- /dev/null
+++ b/test/shared.sh
@@ -0,0 +1,20 @@
+#!/bin/bash
+set -e
+echo -n "Testing $(basename -s .sh $0) ... "
+t=$(pwd)/tmp/$(basename -s .sh $0)
+mkdir -p $t
+
+cat <<EOF | clang -fPIC -c -o $t/a.o -x assembler -
+.globl fn1, fn2
+fn1:
+  call fn2
+EOF
+
+clang -shared  -fuse-ld=`pwd`/../mold -o $t/b.so $t/a.o
+
+readelf --dyn-syms $t/b.so > $t/log
+
+grep -q '0000000000000000     0 NOTYPE  GLOBAL DEFAULT  UND fn2' $t/log
+grep -q '000000000000111c     0 NOTYPE  GLOBAL DEFAULT   16 fn1' $t/log
+
+echo OK