-r: Do not emit .eh_frame if there's no input .eh_frame

elf/output-chunks.cc

@@ -2020,6 +2020,14 @@ template <typename E>
 void EhFrameSection<E>::construct(Context<E> &ctx) {
   Timer t(ctx, "eh_frame");
 
+  // If .eh_frame is missing in all input files, we don't want to
+  // create an output .eh_frame section.
+  if (std::all_of(ctx.objs.begin(), ctx.objs.end(),
+                  [](ObjectFile<E> *file) { return file->cies.empty(); })) {
+    this->shdr.sh_size = 0;
+    return;
+  }
+
   // Remove dead FDEs and assign them offsets within their corresponding
   // CIE group.
   tbb::parallel_for_each(ctx.objs, [&](ObjectFile<E> *file) {

test/elf/relocatable-no-ehframe.sh

@@ -0,0 +1,16 @@
+#!/bin/bash
+. $(dirname $0)/common.inc
+
+# OneTBB isn't tsan-clean
+nm mold | grep -q '__tsan_init' && skip
+
+cat <<EOF | $CC -c -o $t/a.o -xc -fno-unwind-tables -fno-asynchronous-unwind-tables -
+int foo() { return 1; }
+EOF
+
+readelf -WS $t/a.o > $t/log1
+! grep -Fq .eh_frame $t/log1 || false
+
+./mold --relocatable -o $t/b.o $t/a.o
+readelf -WS $t/b.o > $t/log2
+! grep -Fq .eh_frame $t/log2 || false