Guarantee function pointer equivalence

output_chunks.cc

@@ -653,6 +653,10 @@ void DynsymSection::copy_buf() {
     } else if (sym.is_imported() || sym.esym->is_undef()) {
       esym.st_shndx = SHN_UNDEF;
       esym.st_size = 0;
+      if (!config.shared && sym.plt_idx != -1) {
+        // Emit an address for a canonical PLT
+        esym.st_value = sym.get_plt_addr();
+      }
     } else if (!sym.input_section) {
       esym.st_shndx = SHN_ABS;
       esym.st_value = sym.get_addr();

test/canonical-plt.sh

@@ -0,0 +1,27 @@
+#!/bin/bash
+set -e
+cd $(dirname $0)
+echo -n "Testing $(basename -s .sh $0) ... "
+t=$(pwd)/tmp/$(basename -s .sh $0)
+mkdir -p $t
+
+cat <<EOF | cc -o $t/a.so -fPIC -shared -xc -
+void *foo() {
+  return foo;
+}
+EOF
+
+cat <<EOF | cc -o $t/b.o -c -xc - -fno-PIC
+#include <stdio.h>
+
+void *foo();
+
+int main() {
+  printf("%d\n", foo == foo());
+}
+EOF
+
+clang -fuse-ld=`pwd`/../mold -o $t/exe $t/a.so $t/b.o
+$t/exe | grep 1
+
+echo OK