guard against merges with resource and base reloc sections

src/linker/lnk_config.c

@@ -1306,6 +1306,20 @@ lnk_apply_cmd_option_to_config(Arena *arena, LNK_Config *config, String8 cmd_nam
     }
   } break;
 
+  case LNK_CmdSwitch_Merge: {
+    if (value_strings.node_count == 1) {
+      LNK_MergeDirective merge = {0};;
+      if (lnk_parse_merge_directive(push_str8_copy(arena, value_strings.first->string), &merge)) {
+        lnk_merge_directive_list_push(arena, &config->merge_list, merge);
+      } else {
+        lnk_error_cmd_switch(LNK_Warning_InvalidMergeDirectiveFormat, obj_path, lib_path, cmd_switch, "invalid merge directive format expected \"/MERGE:FROM=TO\" but got \"%S\"",
+                             value_strings.first->string);
+      }
+    } else {
+      lnk_error_cmd_switch(LNK_Error_Cmdl, obj_path, lib_path, cmd_switch, "invalid number of parameters %d", value_strings.node_count);
+    }
+  } break;
+
   case LNK_CmdSwitch_Natvis: {
     // warn about invalid natvis extension
     for (String8Node *node = value_strings.first; node != 0; node = node->next) {

src/linker/lnk_error.h

@@ -34,6 +34,7 @@ typedef enum
   LNK_Error_InvalidPath,
   LNK_Error_MultiplyDefinedSymbol,
   LNK_Error_SectRefsDiscardedMemory,
+  LNK_Error_IllegalSectionMerge,
   LNK_Error_StopLast,
   
   LNK_Error_First,
@@ -54,6 +55,7 @@ typedef enum
   LNK_Error_Last,
   
   LNK_Warning_First,
+  LNK_Warning_InvalidMergeDirectiveFormat,
   LNK_Warning_AmbiguousMerge,
   LNK_Warning_AtypicalStartIndex,
   LNK_Warning_Cmdl,

src/linker/lnk_section_table.c

@@ -240,9 +240,26 @@ lnk_section_table_merge(LNK_SectionTable *sectab, LNK_MergeDirectiveList merge_l
 {
   ProfBeginFunction();
   Temp scratch = scratch_begin(0, 0);
+  
   LNK_Section **src_dst = push_array(scratch.arena, LNK_Section *, sectab->id_max);
   for (LNK_MergeDirectiveNode *merge_node = merge_list.first; merge_node != 0; merge_node = merge_node->next) {
     LNK_MergeDirective *merge = &merge_node->data;
+
+    // guard against illegal merges
+    {
+      local_persist String8 illegal_merge_sections[] = {
+        str8_lit_comp(".rsrc"),
+        str8_lit_comp(".reloc"),
+      };
+      for (U64 i = 0; i < ArrayCount(illegal_merge_sections); i += 1) {
+        if (str8_match(merge->src, illegal_merge_sections[i], 0)) {
+          lnk_error(LNK_Error_IllegalSectionMerge, "illegal to merge %S with %S", illegal_merge_sections[i], merge->dst);
+        }
+        if (str8_match(merge->dst, illegal_merge_sections[i], 0)) {
+          lnk_error(LNK_Error_IllegalSectionMerge, "illegal to merge %S with %S", merge->src, illegal_merge_sections[i]);
+        }
+      }
+    }
     
     // are we trying to merge section that was already merged?
     LNK_Section *merge_sect = 0;