handle communal var vs regular non-comdat symbol

src/linker/lnk_symbol_table.c

@@ -181,6 +181,7 @@ lnk_can_replace_symbol(LNK_Symbol *dst, LNK_Symbol *src)
 
   B32 can_replace = 0;
 
+
   // lib vs lib
   if (dst->type == LNK_Symbol_Lib && src->type == LNK_Symbol_Lib) {
     // link.exe picks symbol from lib that is discovered first
@@ -234,52 +235,60 @@ lnk_can_replace_symbol(LNK_Symbol *dst, LNK_Symbol *src)
     else if (dst_interp == COFF_SymbolValueInterp_Abs && src_interp == COFF_SymbolValueInterp_Weak) {
       can_replace = 0;
     }
-    // weak vs regular,common,abs
+    // weak vs (regular, common, abs)
     else if (dst_interp == COFF_SymbolValueInterp_Weak && (src_interp == COFF_SymbolValueInterp_Regular || src_interp == COFF_SymbolValueInterp_Common || src_interp == COFF_SymbolValueInterp_Abs)) {
       can_replace = 1;
     }
-    // regular,common vs regular,common
+    // (regular, common) vs (regular, common)
     else if ((dst_interp == COFF_SymbolValueInterp_Regular || dst_interp == COFF_SymbolValueInterp_Common) && (src_interp == COFF_SymbolValueInterp_Regular || src_interp == COFF_SymbolValueInterp_Common)) {
-      B32 is_dst_single_defn = 0;
+      B32                   dst_is_comdat = 0;
-      B32 is_src_single_defn = 0;
-
       COFF_ComdatSelectType dst_select;
-      U32 dst_section_length;
+      U32                   dst_section_length;
-      U32 dst_check_sum;
+      U32                   dst_check_sum;
       if (dst_interp == COFF_SymbolValueInterp_Regular) {
         U32 dst_comdat_symbol_idx = dst_obj->comdats[dst_parsed.section_number-1];
         if (dst_comdat_symbol_idx != max_U32) {
           COFF_ParsedSymbol secdef = lnk_parsed_symbol_from_coff_symbol_idx(dst_obj, dst_comdat_symbol_idx);
           coff_parse_secdef(secdef, dst_obj->header.is_big_obj, &dst_select, 0, &dst_section_length, &dst_check_sum);
-        } else {
+          dst_is_comdat = 1;
-          is_dst_single_defn = 1;
         }
       } else if (dst_interp == COFF_SymbolValueInterp_Common) {
-        dst_select = COFF_ComdatSelect_Largest;
+        dst_select         = COFF_ComdatSelect_Largest;
         dst_section_length = dst_parsed.value;
-        dst_check_sum = 0;
+        dst_check_sum      = 0;
+        dst_is_comdat      = 1;
       }
 
+      B32                   src_is_comdat = 0;
       COFF_ComdatSelectType src_select;
-      U32 src_section_length;
+      U32                   src_section_length;
-      U32 src_check_sum;
+      U32                   src_check_sum;
       if (src_interp == COFF_SymbolValueInterp_Regular) {
         U32 src_comdat_symbol_idx = src_obj->comdats[src_parsed.section_number-1];
         if (src_comdat_symbol_idx != max_U32) {
           COFF_ParsedSymbol secdef = lnk_parsed_symbol_from_coff_symbol_idx(src_obj, src_comdat_symbol_idx);
           coff_parse_secdef(secdef, src_obj->header.is_big_obj, &src_select, 0, &src_section_length, &src_check_sum);
-        } else {
+          src_is_comdat = 1;
-          is_src_single_defn = 1;
         }
       } else if (src_interp == COFF_SymbolValueInterp_Common) {
-        src_select = COFF_ComdatSelect_Largest;
+        src_select         = COFF_ComdatSelect_Largest;
         src_section_length = src_parsed.value;
-        src_check_sum = 0;
+        src_check_sum      = 0;
+        src_is_comdat      = 1;
       }
 
-      if (is_dst_single_defn || is_src_single_defn) {
+      // regular non-comdat vs communal
-        lnk_error_multiply_defined_symbol(dst, src);
+      if (dst_interp == COFF_SymbolValueInterp_Regular && !dst_is_comdat &&
-      } else {
+          src_interp == COFF_SymbolValueInterp_Common) {
+        can_replace = 0;
+      }
+      // communal vs regular non-comdat
+      else if (dst_interp == COFF_SymbolValueInterp_Common && 
+               src_interp == COFF_SymbolValueInterp_Regular && !src_is_comdat) {
+        can_replace = 1;
+      }
+      // handle COMDATs
+      else if (dst_is_comdat && src_is_comdat) {
         // handle objs compiled with /GR- and /GR
         if ((src_select == COFF_ComdatSelect_Any && dst_select == COFF_ComdatSelect_Largest)) {
           src_select = COFF_ComdatSelect_Largest;
@@ -331,14 +340,7 @@ lnk_can_replace_symbol(LNK_Symbol *dst, LNK_Symbol *src)
           } break;
           case COFF_ComdatSelect_Largest: {
             if (dst_section_length == src_section_length) {
-              if (dst_interp == COFF_SymbolValueInterp_Common) {
+              can_replace = src_obj->input_idx < dst_obj->input_idx;
-                // handle communal variable
-                //
-                // MSVC CRT relies on this behaviour (e.g. __scrt_ucrt_dll_is_in_use in ucrt_detection.c)
-                can_replace = 1;
-              } else {
-                can_replace = src_obj->input_idx < dst_obj->input_idx;
-              }
             } else {
               can_replace = dst_section_length < src_section_length;
             }
@@ -355,6 +357,8 @@ lnk_can_replace_symbol(LNK_Symbol *dst, LNK_Symbol *src)
                         "%S: COMDAT selection conflict detected, current selection %S, leader selection %S from %S", 
                         src->name, src_select_str, dst_select_str, dst_obj);
         }
+      } else {
+        lnk_error_multiply_defined_symbol(dst, src);
       }
     } else {
       lnk_error(LNK_Error_InvalidPath, "unable to find a suitable replacement logic for symbol combination");

src/torture/torture.c

@@ -2953,7 +2953,74 @@ t_include(void)
 }
 
 internal T_Result
-t_communal_var(void)
+t_communal_var_vs_regular(void)
+{
+  Temp scratch = scratch_begin(0,0);
+  T_Result result = T_Result_Fail;
+
+  {
+    COFF_ObjWriter *obj_writer = coff_obj_writer_alloc(0, COFF_MachineType_X64);
+    coff_obj_writer_push_symbol_common(obj_writer, str8_lit("TEST"), 1);
+    String8 obj = coff_obj_writer_serialize(scratch.arena, obj_writer);
+    coff_obj_writer_release(&obj_writer);
+    if (!t_write_file(str8_lit("communal.obj"), obj)) { goto exit; }
+  }
+
+  {
+    COFF_ObjWriter *obj_writer = coff_obj_writer_alloc(0, COFF_MachineType_X64);
+    COFF_ObjSection *sect = t_push_data_section(obj_writer, str8_lit("test"));
+    coff_obj_writer_push_symbol_extern(obj_writer, str8_lit("TEST"), 0, sect);
+    String8 obj = coff_obj_writer_serialize(scratch.arena, obj_writer);
+    coff_obj_writer_release(&obj_writer);
+    if (!t_write_file(str8_lit("defn.obj"), obj)) { goto exit; }
+  }
+
+  {
+    COFF_ObjWriter *obj_writer = coff_obj_writer_alloc(0, COFF_MachineType_X64);
+    U8 text[] = {
+      0x48, 0xC7, 0xC0, 0x00, 0x00, 0x00, 0x00,  // mov rax, $imm
+      0xC3 // ret
+    };
+    COFF_ObjSection *sect = coff_obj_writer_push_section(obj_writer, str8_lit(".text"), PE_TEXT_SECTION_FLAGS, str8_array_fixed(text));
+    coff_obj_writer_push_symbol_extern(obj_writer, str8_lit("entry"), 0, sect);
+    COFF_ObjSymbol *symbol = coff_obj_writer_push_symbol_undef(obj_writer, str8_lit("TEST"));
+    coff_obj_writer_section_push_reloc_voff(obj_writer, sect, 0, symbol);
+    String8 obj = coff_obj_writer_serialize(scratch.arena, obj_writer);
+    coff_obj_writer_release(&obj_writer);
+    if (!t_write_file(str8_lit("entry.obj"), obj)) {
+      goto exit;
+    }
+  }
+
+  // linker should replace communal TEST with .data TEST
+  int linker_exit_code;
+
+  linker_exit_code = t_invoke_linkerf("/subsystem:console /entry:entry /out:a.exe communal.obj defn.obj entry.obj");
+  if (linker_exit_code != 0) { goto exit; }
+
+  linker_exit_code = t_invoke_linkerf("/subsystem:console /entry:entry /out:b.exe defn.obj communal.obj entry.obj");
+  if (linker_exit_code != 0) { goto exit; }
+
+  char *exes[] = { "a.exe", "b.exe" };
+  for (U64 i = 0; i < ArrayCount(exes); i += 1) {
+    String8             exe           = t_read_file(scratch.arena, str8_cstring(exes[i]));
+    PE_BinInfo          pe            = pe_bin_info_from_data(scratch.arena, exe);
+    COFF_SectionHeader *section_table = (COFF_SectionHeader *)str8_substr(exe, pe.section_table_range).str;
+    String8             string_table  = str8_substr(exe, pe.string_table_range);
+    COFF_SectionHeader *data_sect     = t_coff_section_header_from_name(string_table, section_table, pe.section_count, str8_lit(".data"));
+    if (!data_sect) { goto exit; }
+    String8             data          = str8_substr(exe, rng_1u64(data_sect->foff, data_sect->foff + data_sect->vsize));
+    if (!str8_match(data, str8_lit("test"), 0)) { goto exit; }
+  }
+
+  result = T_Result_Pass;
+exit:;
+  scratch_end(scratch);
+  return result;
+}
+
+internal T_Result
+t_communal_var_vs_regular_comdat(void)
 {
   Temp scratch = scratch_begin(0,0);
   T_Result result = T_Result_Fail;
@@ -3187,7 +3254,8 @@ entry_point(CmdLine *cmdline)
     { "comdat_associative_out_of_bounds", t_comdat_associative_out_of_bounds },
     { "alt_name",                         t_alt_name                         },
     { "include",                          t_include                          },
-    { "communal_var",                     t_communal_var                     },
+    { "communal_var_vs_regular_comdat",   t_communal_var_vs_regular_comdat   },
+    { "communal_var_vs_regular",          t_communal_var_vs_regular          },
     { "import_kernel32",                  t_import_kernel32                  },
     { "delay_import_user32",              t_delay_import_user32              },
     //{ "import_export",        t_import_export        },