Fix all undefined behaviors found by UBsan

elf/dwarf.cc

@@ -26,9 +26,9 @@ read_compunits(Context<E> &ctx, ObjectFile<E> &file) {
   while (!data.empty()) {
     if (data.size() < 4)
       Fatal(ctx) << *file.debug_info << ": corrupted .debug_info";
-    if (*(u32 *)data.data() == 0xffffffff)
+    if (*(ul32 *)data.data() == 0xffffffff)
       Fatal(ctx) << *file.debug_info << ": --gdb-index: DWARF64 not supported";
-    i64 len = *(u32 *)data.data() + 4;
+    i64 len = *(ul32 *)data.data() + 4;
     vec.push_back(data.substr(0, len));
     data = data.substr(len);
   }
@@ -258,7 +258,7 @@ inline u64 DebugInfoReader<E>::read(u64 form) {
   case DW_FORM_strx2:
   case DW_FORM_addrx2:
   case DW_FORM_ref2: {
-    u64 val = *(u16 *)cu;
+    u64 val = *(ul16 *)cu;
     cu += 2;
     return val;
   }
@@ -450,7 +450,7 @@ read_address_areas(Context<E> &ctx, ObjectFile<E> &file, i64 offset) {
       Fatal(ctx) << file << ": --gdb-index: missing DW_AT_rnglists_base";
 
     u8 *base = buf + *rnglists_base;
-    return read_rnglist_range(ctx, file, base + *(u32 *)base, addrx);
+    return read_rnglist_range(ctx, file, base + *(ul32 *)base, addrx);
   }
 
   // Handle a contiguous address range.

elf/elf.h

@@ -1270,64 +1270,64 @@ struct Elf64Rela {
 };
 
 struct Elf32Rela {
-  u32 r_offset;
-  u32 r_type : 8;
-  u32 r_sym : 24;
-  i32 r_addend;
+  ul32 r_offset;
+  u8 r_type;
+  ul24 r_sym;
+  il32 r_addend;
 };
 
 struct Elf64Dyn {
-  u64 d_tag;
-  u64 d_val;
+  ul64 d_tag;
+  ul64 d_val;
 };
 
 struct Elf32Dyn {
-  u32 d_tag;
-  u32 d_val;
+  ul32 d_tag;
+  ul32 d_val;
 };
 
 struct ElfVerneed {
-  u16 vn_version;
-  u16 vn_cnt;
-  u32 vn_file;
-  u32 vn_aux;
-  u32 vn_next;
+  ul16 vn_version;
+  ul16 vn_cnt;
+  ul32 vn_file;
+  ul32 vn_aux;
+  ul32 vn_next;
 };
 
 struct ElfVernaux {
-  u32 vna_hash;
-  u16 vna_flags;
-  u16 vna_other;
-  u32 vna_name;
-  u32 vna_next;
+  ul32 vna_hash;
+  ul16 vna_flags;
+  ul16 vna_other;
+  ul32 vna_name;
+  ul32 vna_next;
 };
 
 struct ElfVerdef {
-  u16 vd_version;
-  u16 vd_flags;
-  u16 vd_ndx;
-  u16 vd_cnt;
-  u32 vd_hash;
-  u32 vd_aux;
-  u32 vd_next;
+  ul16 vd_version;
+  ul16 vd_flags;
+  ul16 vd_ndx;
+  ul16 vd_cnt;
+  ul32 vd_hash;
+  ul32 vd_aux;
+  ul32 vd_next;
 };
 
 struct ElfVerdaux {
-  u32 vda_name;
-  u32 vda_next;
+  ul32 vda_name;
+  ul32 vda_next;
 };
 
 struct Elf64Chdr {
-  u32 ch_type;
-  u32 ch_reserved;
-  u64 ch_size;
-  u64 ch_addralign;
+  ul32 ch_type;
+  ul32 ch_reserved;
+  ul64 ch_size;
+  ul64 ch_addralign;
 };
 
 struct Elf32Chdr {
-  u32 ch_type;
-  u32 ch_size;
-  u32 ch_addralign;
+  ul32 ch_type;
+  ul32 ch_size;
+  ul32 ch_addralign;
 };
 
 struct ElfNhdr {

elf/mapfile.cc

@@ -40,6 +40,9 @@ static Map<E> get_map(Context<E> &ctx) {
     }
   });
 
+  if (map.size() <= 1)
+    return map;
+
   tbb::parallel_for(map.range(), [](const typename Map<E>::range_type &range) {
     for (auto it = range.begin(); it != range.end(); it++) {
       std::vector<Symbol<E> *> &vec = it->second;

elf/output-chunks.cc

@@ -1217,6 +1217,8 @@ void DynsymSection<E>::add_symbol(Context<E> &ctx, Symbol<E> *sym) {
 template <typename E>
 void DynsymSection<E>::finalize(Context<E> &ctx) {
   Timer t(ctx, "DynsymSection::finalize");
+  if (symbols.empty())
+    return;
 
   // We need a stable sort for build reproducibility, but parallel_sort
   // isn't stable, so we use this struct to make it stable.