Report an error if a mergeable/merged section is too large

We use u32 as an index into mergeable/merged sections, so we cannot
handle extremely large sections.

common/common.h

@@ -520,10 +520,6 @@ inline bool remove_prefix(std::string_view &s, std::string_view prefix) {
   return false;
 }
 
-//
-// Concurrent Map
-//
-
 static inline void pause() {
 #if defined(__x86_64__)
   asm volatile("pause");
@@ -532,6 +528,10 @@ static inline void pause() {
 #endif
 }
 
+//
+// Concurrent Map
+//
+
 // This is an implementation of a fast concurrent hash map. Unlike
 // ordinary hash tables, this impl just aborts if it becomes full.
 // So you need to give a correct estimation of the final size before

elf/input-files.cc

@@ -728,6 +728,9 @@ split_section(Context<E> &ctx, InputSection<E> &sec) {
   std::string_view data = sec.contents;
   m->contents = sec.contents;
 
+  if (data.size() > UINT32_MAX)
+    Fatal(ctx) << sec << ": mergeable section too large";
+
   // Split sections
   if (shdr.sh_flags & SHF_STRINGS) {
     for (i64 pos = 0; pos < data.size();) {

elf/output-chunks.cc

@@ -1990,6 +1990,9 @@ void MergedSection<E>::assign_offsets(Context<E> &ctx) {
 
   this->shdr.sh_size = shard_offsets[map.NUM_SHARDS];
   this->shdr.sh_addralign = alignment;
+
+  if (this->shdr.sh_size > UINT32_MAX)
+    Fatal(ctx) << this->name << ": output section too large";
 }
 
 template <typename E>