From bbb825adf446f45a5fe66aec6127fe70c782b65f Mon Sep 17 00:00:00 2001
From: Nikita Smith <git.nikita.smith@gmail.com>
Date: Wed, 11 Jun 2025 09:08:31 -0700
Subject: [PATCH] extract hotpatch flag from compile symbol

---
 src/linker/codeview_ext/codeview.c | 11 ++++++--
 src/linker/codeview_ext/codeview.h |  1 +
 src/linker/lnk_obj.c               | 40 ++++++++++++++++++++++++++++++
 src/linker/lnk_obj.h               |  1 +
 4 files changed, 51 insertions(+), 2 deletions(-)

diff --git a/src/linker/codeview_ext/codeview.c b/src/linker/codeview_ext/codeview.c
index b932a4be..af4aeba7 100644
--- a/src/linker/codeview_ext/codeview.c
+++ b/src/linker/codeview_ext/codeview.c
@@ -1213,9 +1213,10 @@ cv_str8_list_from_debug_t_parallel(TP_Context *tp, Arena *arena, CV_DebugT debug
 // $$Symbols
 
 internal void
-cv_parse_symbol_sub_section(Arena *arena, CV_SymbolList *list, U64 offset_base, String8 data, U64 align)
+cv_parse_symbol_sub_section_capped(Arena *arena, CV_SymbolList *list, U64 offset_base, String8 data, U64 align, U64 cap)
 {
-  for (U64 cursor = 0, opl = data.size; cursor < opl; ) {
+  U64 count = 0;
+  for (U64 cursor = 0, opl = data.size; cursor < opl && count < cap; count += 1) {
     // read symbol header
     CV_SymbolHeader header;
     cursor += str8_deserial_read_struct(data, cursor, &header);
@@ -1249,6 +1250,12 @@ cv_parse_symbol_sub_section(Arena *arena, CV_SymbolList *list, U64 offset_base,
   }
 }
 
+internal void
+cv_parse_symbol_sub_section(Arena *arena, CV_SymbolList *list, U64 offset_base, String8 data, U64 align)
+{
+  cv_parse_symbol_sub_section_capped(arena, list, offset_base, data, align, max_U64);
+}
+
 internal CV_SymbolList
 cv_symbol_list_from_data_list(Arena *arena, String8List data_list, U64 align)
 {
diff --git a/src/linker/codeview_ext/codeview.h b/src/linker/codeview_ext/codeview.h
index d4b4ac4e..3b0315ad 100644
--- a/src/linker/codeview_ext/codeview.h
+++ b/src/linker/codeview_ext/codeview.h
@@ -432,6 +432,7 @@ internal String8List cv_str8_list_from_debug_t_parallel(TP_Context *tp, Arena *a
 //~ Sub Section helpers
 
 // $$Symbols
+internal void              cv_parse_symbol_sub_section_capped(Arena *arena, CV_SymbolList *list, U64 offset_base, String8 data, U64 align, U64 cap);
 internal void              cv_parse_symbol_sub_section(Arena *arena, CV_SymbolList *list, U64 offset_base, String8 data, U64 align);
 internal void              cv_symbol_list_push_node(CV_SymbolList *list, CV_SymbolNode *node);
 internal CV_SymbolNode *   cv_symbol_list_push(Arena *arena, CV_SymbolList *list);
diff --git a/src/linker/lnk_obj.c b/src/linker/lnk_obj.c
index 40540dde..16879a0d 100644
--- a/src/linker/lnk_obj.c
+++ b/src/linker/lnk_obj.c
@@ -224,6 +224,45 @@ THREAD_POOL_TASK_FUNC(lnk_obj_initer)
 
     scratch_end(scratch);
   }
+  
+  //
+  // Extract obj features from compile symbol in .debug$S
+  //
+  B8 hotpatch = 0;
+  {
+    Temp scratch = scratch_begin(&arena, 1);
+
+    CV_Symbol comp_symbol = {0};
+    for (U64 sect_idx = 0; sect_idx < obj->header.section_count_no_null; sect_idx += 1) {
+      COFF_SectionHeader *sect_header = &coff_section_table[sect_idx];
+      String8 name = str8_cstring_capped_reverse(sect_header->name, sect_header->name+sizeof(sect_header->name));
+      if (str8_match(name, str8_lit(".debug$S"), 0)) {
+        Temp temp = temp_begin(scratch.arena);
+        String8 debug_s_data = str8_substr(input->data, rng_1u64(sect_header->foff, sect_header->foff+sect_header->fsize));
+        CV_DebugS debug_s = cv_parse_debug_s(temp.arena, debug_s_data);
+        for (String8Node *symbols_n = debug_s.data_list[CV_C13SubSectionIdxKind_Symbols].first; symbols_n != 0; symbols_n = symbols_n->next) {
+          CV_SymbolList symbol_list = {0};
+          cv_parse_symbol_sub_section_capped(scratch.arena, &symbol_list, 0, symbols_n->string, CV_SymbolAlign, 2);
+          if (symbol_list.first->data.kind == CV_SymKind_COMPILE3) {
+            comp_symbol = symbol_list.first->data;
+            goto found_comp_symbol;
+          } else if (symbol_list.last->data.kind == CV_SymKind_COMPILE3) {
+            comp_symbol = symbol_list.last->data;
+            goto found_comp_symbol;
+          }
+        }
+        temp_end(temp);
+      }
+    }
+    found_comp_symbol:;
+
+    if (comp_symbol.kind == CV_SymKind_COMPILE3 && comp_symbol.data.size >= sizeof(CV_SymCompile3)) {
+      CV_SymCompile3 *comp = (CV_SymCompile3 *)comp_symbol.data.str;
+      hotpatch = !!(comp->flags & CV_Compile3Flag_HotPatch);
+    }
+
+    scratch_end(scratch);
+  }
 
   // fill out obj
   obj->data      = input->data;
@@ -232,6 +271,7 @@ THREAD_POOL_TASK_FUNC(lnk_obj_initer)
   obj->input_idx = obj_idx;
   obj->header    = header;
   obj->comdats   = comdats;
+  obj->hotpatch  = hotpatch;
 
   ProfEnd();
 }
diff --git a/src/linker/lnk_obj.h b/src/linker/lnk_obj.h
index 436c155d..3f79365c 100644
--- a/src/linker/lnk_obj.h
+++ b/src/linker/lnk_obj.h
@@ -13,6 +13,7 @@ typedef struct LNK_Obj
   U32                 input_idx;
   COFF_FileHeaderInfo header;
   U32                *comdats;
+  B8                  hotpatch;
 } LNK_Obj;
 
 typedef struct LNK_ObjNode