From 2c5fb7e7ef4ba7d915bef269bd3d3d67ea48bda5 Mon Sep 17 00:00:00 2001
From: Nikita Smith <git.nikita.smith@gmail.com>
Date: Thu, 8 May 2025 16:30:54 -0700
Subject: [PATCH] guard against merges with resource and base reloc sections

---
 src/linker/lnk_config.c        | 14 ++++++++++++++
 src/linker/lnk_error.h         |  2 ++
 src/linker/lnk_section_table.c | 17 +++++++++++++++++
 src/torture/torture.c          | 33 +++++++++++++++++++++++++++++++--
 4 files changed, 64 insertions(+), 2 deletions(-)

diff --git a/src/linker/lnk_config.c b/src/linker/lnk_config.c
index 756b3b01..e6a1f1ce 100644
--- a/src/linker/lnk_config.c
+++ b/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) {
diff --git a/src/linker/lnk_error.h b/src/linker/lnk_error.h
index b00f8491..d1fa096c 100644
--- a/src/linker/lnk_error.h
+++ b/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,
diff --git a/src/linker/lnk_section_table.c b/src/linker/lnk_section_table.c
index ccc48343..e5726782 100644
--- a/src/linker/lnk_section_table.c
+++ b/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;
diff --git a/src/torture/torture.c b/src/torture/torture.c
index 4663d81d..64127fec 100644
--- a/src/torture/torture.c
+++ b/src/torture/torture.c
@@ -1333,7 +1333,36 @@ t_base_relocs(void)
   }
 
   String8 out_name = str8_lit("a.exe");
-  int linker_exit_code = t_invoke_linkerf("/subsystem:console /entry:%S /dynamicbase /largeaddressaware:no /out:%S %S %S", entry_name, out_name, main_obj_name, func_obj_name);
+  int linker_exit_code = t_invoke_linkerf("/subsystem:console /entry:my_entry /dynamicbase /largeaddressaware:no /out:a.exe main.obj func.obj");
+  if (linker_exit_code != 0) {
+    goto exit;
+  }
+
+  // it is illegal to merge .reloc with other sections
+  linker_exit_code = t_invoke_linkerf("/subsystem:console /entry:my_entry /dynamicbase /largeaddressaware:no /out:a.exe /merge:.reloc=.rdata main.obj func.obj");
+  if (t_ident_linker() == T_Linker_RAD) {
+    if (linker_exit_code != LNK_Error_IllegalSectionMerge) {
+      goto exit;
+    }
+  } else {
+    if (linker_exit_code == 0) {
+      goto exit;
+    }
+  }
+
+  // the other way around is illegal too
+  linker_exit_code = t_invoke_linkerf("/subsystem:console /entry:my_entry /dynamicbase /largeaddressaware:no /out:a.exe /merge:.rdata=.reloc main.obj func.obj");
+  if (t_ident_linker() == T_Linker_RAD) {
+    if (linker_exit_code != LNK_Error_IllegalSectionMerge) {
+      goto exit;
+    }
+  } else {
+    if (linker_exit_code == 0) {
+      goto exit;
+    }
+  }
+
+  result = T_Result_Pass;
   
 exit:;
   scratch_end(scratch);
@@ -1602,7 +1631,7 @@ entry_point(CmdLine *cmdline)
     { "flag_conf",           t_flag_conf           },
     { "invalid_bss",         t_invalid_bss         },
     { "common_block",        t_common_block        },
-    //{ "base_relocs",        t_base_relocs       },
+    { "base_relocs",         t_base_relocs         },
     { "simple_lib_test",     t_simple_lib_test     },
     { "import_export",       t_import_export       },
   };