create section contribution for common block

src/linker/lnk.c

@@ -3399,7 +3399,7 @@ THREAD_POOL_TASK_FUNC(lnk_patch_virtual_offsets_and_sizes_in_obj_section_headers
     if (~sect_header->flags & COFF_SectionFlag_LnkRemove) {
       LNK_SectionContrib *sc   = task->sect_map[obj_idx][sect_idx];
       LNK_Section        *sect = task->image_sects.v[sc->u.sect_idx];
-      sect_header->vsize = sc->u.size;
+      sect_header->vsize = lnk_size_from_section_contribution(sc);
       sect_header->voff  = sect->voff + sc->u.off;
     }
   }
@@ -3423,7 +3423,7 @@ THREAD_POOL_TASK_FUNC(lnk_patch_file_offsets_and_sizes_in_obj_section_headers_ta
       LNK_SectionContrib *sc   = task->sect_map[obj_idx][sect_idx];
       LNK_Section        *sect = task->image_sects.v[sc->u.sect_idx];
       if (~sect->flags & COFF_SectionFlag_CntUninitializedData) {
-        sect_header->fsize = sc->u.size;
+        sect_header->fsize = lnk_size_from_section_contribution(sc);
         sect_header->foff  = sect->foff + sc->u.off;
       }
     }
@@ -3880,6 +3880,7 @@ lnk_build_image(TP_Arena *arena, TP_Context *tp, LNK_Config *config, LNK_SymbolT
   lnk_section_table_push(sectab, str8_lit(".rdata"), PE_RDATA_SECTION_FLAGS);
   lnk_section_table_push(sectab, str8_lit(".data"),  PE_DATA_SECTION_FLAGS);
   lnk_section_table_push(sectab, str8_lit(".bss"),   PE_BSS_SECTION_FLAGS);
+  LNK_Section *common_block_sect = lnk_section_table_search(sectab, str8_lit(".bss"), PE_BSS_SECTION_FLAGS);
 
   LNK_BuildImageTask task = {0};
   task.symtab        = symtab;
@@ -4032,7 +4033,6 @@ lnk_build_image(TP_Arena *arena, TP_Context *tp, LNK_Config *config, LNK_SymbolT
     // TODO: build common block in .bss and merge with .data
     U64                     common_block_contribs_count;
     LNK_CommonBlockContrib *common_block_contribs;
-    LNK_Section            *common_block_sect;
     {
       ProfBegin("Build Common Block");
 
@@ -4078,23 +4078,35 @@ lnk_build_image(TP_Arena *arena, TP_Context *tp, LNK_Config *config, LNK_SymbolT
       ProfEnd();
 
       if (common_block_contribs_count) {
-        ProfBeginV("Assign Common Block Offsets [count %llu]", common_block_contribs_count);
+        ProfBeginV("Make Common Block [count %llu]", common_block_contribs_count);
 
-        // grab .bss section
+        // sort common blocks from for tighter packing
-        common_block_sect = lnk_section_table_search(sectab, str8_lit(".bss"), PE_BSS_SECTION_FLAGS);
-
-        // sort common blocks from largest to smallest for tighter packing
         radsort(common_block_contribs, common_block_contribs_count, lnk_common_block_contrib_is_before);
 
-        // compute common block offsets
+        // compute .bss virtual size - this marks start of the common block
+        lnk_finalize_section_layout(sectab, common_block_sect, config->file_align);
+        U64 common_block_cursor = common_block_sect->vsize;
+
+        // compute and assign offsets into the common block
         for (U64 contrib_idx = 0; contrib_idx < common_block_contribs_count; contrib_idx += 1) {
           LNK_CommonBlockContrib *contrib = &common_block_contribs[contrib_idx];
           U32 size = contrib->u.size;
           U32 align = Min(32, u64_up_to_pow2(size)); // link.exe caps align at 32 bytes
-          common_block_sect->vsize = AlignPow2(common_block_sect->vsize, align);
+          common_block_cursor = AlignPow2(common_block_cursor, align);
-          contrib->u.offset = common_block_sect->vsize;
+          contrib->u.offset = common_block_cursor;
-          common_block_sect->vsize += size;
+          common_block_cursor += size;
         }
+
+        // append common block's contribution
+        LNK_SectionContribChunk *common_block_chunk = lnk_section_contrib_chunk_list_push_chunk(sectab->arena, &common_block_sect->contribs, 1, str8(0,0));
+        LNK_SectionContrib      *common_block_sc    = lnk_section_contrib_chunk_push(common_block_chunk, 1);
+        common_block_sc->u.obj_idx      = max_U32;
+        common_block_sc->u.obj_sect_idx = max_U32;
+        common_block_sc->align          = 1;
+        common_block_sc->node.next      = 0;
+        common_block_sc->node.string    = str8(0, common_block_cursor - common_block_sect->vsize);
+        common_block_sc->data_list      = &common_block_sc->node;
+
         ProfEnd();
       }
 
@@ -4140,10 +4152,11 @@ lnk_build_image(TP_Arena *arena, TP_Context *tp, LNK_Config *config, LNK_SymbolT
         LNK_Section *final_sect = lnk_finalized_section_from_id(sectab, sect->merge_id);
         LNK_SectionContrib *first_sc = lnk_get_first_section_contrib(sect);
         LNK_SectionContrib *last_sc  = lnk_get_last_section_contrib(sect);
+        U64 last_sc_size = lnk_size_from_section_contribution(last_sc);
         sect->voff     = final_sect->voff + first_sc->u.off;
-        sect->vsize    = (last_sc->u.off - first_sc->u.off) + last_sc->u.size;
+        sect->vsize    = (last_sc->u.off - first_sc->u.off) + last_sc_size;
         sect->foff     = final_sect->foff + first_sc->u.off;
-        sect->fsize    = (last_sc->u.off - first_sc->u.off) + last_sc->u.size;
+        sect->fsize    = (last_sc->u.off - first_sc->u.off) + last_sc_size;
         sect->sect_idx = final_sect->sect_idx;
       }
 
@@ -4259,7 +4272,6 @@ lnk_build_image(TP_Arena *arena, TP_Context *tp, LNK_Config *config, LNK_SymbolT
 
     image_header_sc->align     = config->file_align;
     image_header_sc->data_list = image_header_data.first;
-    image_header_sc->u.size    = safe_cast_u32(image_header_data.total_size);
 
     lnk_finalize_section_layout(sectab, image_header_sect, config->file_align);
   }
@@ -4302,7 +4314,7 @@ lnk_build_image(TP_Arena *arena, TP_Context *tp, LNK_Config *config, LNK_SymbolT
             Assert(sc->u.off >= prev_sc_opl);
             U64 fill_size = sc->u.off - prev_sc_opl;
             MemorySet(image_data.str + sect->foff + prev_sc_opl, fill_byte, fill_size);
-            prev_sc_opl = sc->u.off + sc->u.size;
+            prev_sc_opl = sc->u.off + lnk_size_from_section_contribution(sc);
 
             // copy contrib contents
             {
@@ -4583,8 +4595,8 @@ lnk_build_rad_map(Arena *arena, String8 image_data, U64 thread_count, U64 objs_c
 
         U64        file_off   = image_section_table[sc->u.sect_idx]->foff + sc->u.off;
         U64        virt_off   = image_section_table[sc->u.sect_idx]->voff + sc->u.off;
-        U64        virt_size  = sc->u.size;
+        U64        virt_size  = lnk_size_from_section_contribution(sc);
-        U64        file_size  = sc->u.size;
+        U64        file_size  = lnk_size_from_section_contribution(sc);
         String8    sc_data    = str8_substr(image_data, rng_1u64(file_off, file_off + virt_size));
 
         U128 sc_hash = {0};

src/linker/lnk_section_table.c

@@ -100,6 +100,16 @@ lnk_section_array_from_list(Arena *arena, LNK_SectionList list)
   return result;
 }
 
+internal U64
+lnk_size_from_section_contribution(LNK_SectionContrib *sc)
+{
+  U64 size = 0;
+  for (String8Node *n = sc->data_list; n != 0; n = n->next) {
+    size += n->string.size;
+  }
+  return size;
+}
+
 internal U64
 lnk_voff_from_section_contrib(COFF_SectionHeader **image_section_table, LNK_SectionContrib *sc)
 {
@@ -120,7 +130,7 @@ internal U64
 lnk_fopl_from_section_contrib(COFF_SectionHeader **image_section_table, LNK_SectionContrib *sc)
 {
   U64 foff = lnk_foff_from_section_contrib(image_section_table, sc);
-  return foff + sc->u.size;
+  return foff + lnk_size_from_section_contribution(sc);
 }
 
 internal LNK_SectionContrib *
@@ -150,7 +160,7 @@ lnk_get_section_contrib_size(LNK_Section *sect)
 {
   LNK_SectionContrib *first_sc = lnk_get_first_section_contrib(sect);
   LNK_SectionContrib *last_sc = lnk_get_last_section_contrib(sect);
-  U64 size = (last_sc->u.off - first_sc->u.off) + last_sc->u.size;
+  U64 size = (last_sc->u.off - first_sc->u.off) + lnk_size_from_section_contribution(last_sc);
   return size;
 }
 
@@ -468,16 +478,11 @@ lnk_finalize_section_layout(LNK_SectionTable *sectab, LNK_Section *sect, U64 fil
       U64 sc_off = cursor;
 
       // compute contrib size
-      U64 sc_size = 0;
+      U64 sc_size = lnk_size_from_section_contribution(sc);
-      for (String8Node *data_n = sc->data_list; data_n != 0; data_n = data_n->next) {
-        sc_size += data_n->string.size;
-      }
-
       cursor += sc_size;
 
       // assign offset and size
-      sc->u.off  = sc_off;
+      sc->u.off = sc_off;
-      sc->u.size = sc_size;
     }
   }
   ProfEnd();

src/linker/lnk_section_table.h

@@ -5,26 +5,22 @@
 
 typedef struct LNK_SectionContrib
 {
+  String8Node  node;      // most contributions require at least one data node, so preallocate it here
+  String8Node *data_list; // list of data nodes that contribute to final section
   union {
+    // used before section layout is finalized
     struct {
-      U32 obj_idx;
+      U32 obj_idx;      // index of the input obj that contributes to the image section
-      U32 obj_sect_idx;
+      U32 obj_sect_idx; // index into contributing obj's section table
     };
+    // used after section layout is finalized
     struct {
-      U32 off;
+      U32 off;      // contribution offset within the image section
-      U32 size;
+      U16 sect_idx; // section index in the image
-      U16 sect_idx;
+      U8  unused[2];
     };
   } u;
-
+  U16 align; // alignment of the contribution in the image
-  U16 align;
-
-  union {
-    String8Node *data_list;
-    U64          bss_size;
-  };
-
-  String8Node node;
 } LNK_SectionContrib;
 
 typedef struct LNK_CommonBlockContrib
@@ -119,6 +115,7 @@ internal LNK_SectionArray lnk_section_array_from_list(Arena *arena, LNK_SectionL
 
 ////////////////////////////////
 
+internal U64 lnk_size_from_section_contrib(LNK_SectionContrib *sc);
 internal U64 lnk_voff_from_section_contrib(COFF_SectionHeader **image_section_table, LNK_SectionContrib *sc);
 internal U64 lnk_foff_from_section_contrib(COFF_SectionHeader **image_section_table, LNK_SectionContrib *sc);
 internal U64 lnk_fopl_from_section_contrib(COFF_SectionHeader **image_section_table, LNK_SectionContrib *sc);

src/torture/torture.c

@@ -1629,6 +1629,7 @@ t_common_block(void)
     COFF_ObjSymbol *symbol = coff_obj_writer_push_symbol_common(obj_writer, str8_lit("A"), 3);
     COFF_ObjSection *data_sect = t_push_data_section(obj_writer, str8_array_fixed(a_data));
     data_sect->flags |= COFF_SectionFlag_Align1Bytes;
+    coff_obj_writer_push_section(obj_writer, str8_lit(".bss"), PE_BSS_SECTION_FLAGS, str8(0, 1)); // shift common block's initial position
     coff_obj_writer_section_push_reloc(obj_writer, data_sect, 0, symbol, COFF_Reloc_X64_Addr32);
     String8 a_obj = coff_obj_writer_serialize(scratch.arena, obj_writer);
     coff_obj_writer_release(&obj_writer);
@@ -1672,14 +1673,14 @@ t_common_block(void)
   if (data_sect == 0) { goto exit; }
 
   // blocks must be sorted in descending order to reduce alignment padding
-  if (comm_sect->vsize != 0xB) { goto exit; }
+  if (comm_sect->vsize != 0x13) { goto exit; }
 
   // ensure linker correctly patched addresses for symbols pointing into common block
   String8             data      = str8_substr(exe, rng_1u64(data_sect->foff, data_sect->foff + data_sect->fsize));
   U32                *a_addr    = (U32 *)data.str;
   U64                *b_addr    = (U64 *)(data.str + sizeof(a_data));
-  if (*a_addr != (pe.image_base + comm_sect->voff + 0x8)) { goto exit; }
+  if (*a_addr != (pe.image_base + comm_sect->voff + 0x10)) { goto exit; }
-  if (*b_addr != (pe.image_base + comm_sect->voff + 0x0)) { goto exit; }
+  if (*b_addr != (pe.image_base + comm_sect->voff + 0x8)) { goto exit; }
   
   result = T_Result_Pass;
 exit:;