From f330bde8aae1c8667fbc71ae56285b74faa112b3 Mon Sep 17 00:00:00 2001
From: Martins Mozeiko <martins.mozeiko@gmail.com>
Date: Fri, 16 Jan 2026 16:40:30 -0800
Subject: [PATCH] better callstack for null calls

This improves callstack in win32 unhandled exception handler when
indirect call to NULL happens. Before no call stack was printed at
all, so it was hard to know what happened. Now call stack explicitly
will print out [NULL] stack entry + rest of call stack entries. This
is done by manually looking up return address from call stack when
possible.

Also fixes wine compatibility for os_commit function. Wine does not
support RIO buffer functions.
---
 src/os/core/win32/os_core_win32.c | 58 +++++++++++++++++++++++--------
 1 file changed, 43 insertions(+), 15 deletions(-)

diff --git a/src/os/core/win32/os_core_win32.c b/src/os/core/win32/os_core_win32.c
index 6e681f0e..8aaf0fda 100644
--- a/src/os/core/win32/os_core_win32.c
+++ b/src/os/core/win32/os_core_win32.c
@@ -208,7 +208,11 @@ internal B32
 os_commit(void *ptr, U64 size)
 {
   B32 result = (VirtualAlloc(ptr, size, MEM_COMMIT, PAGE_READWRITE) != 0);
-  w32_rio_functions.RIODeregisterBuffer(w32_rio_functions.RIORegisterBuffer(ptr, size));
+  if (w32_rio_functions.RIORegisterBuffer)
+  {
+    // wine does not implement these functions
+    w32_rio_functions.RIODeregisterBuffer(w32_rio_functions.RIORegisterBuffer(ptr, size));
+  }
   return result;
 }
 
@@ -1565,7 +1569,43 @@ win32_exception_filter(EXCEPTION_POINTERS* exception_ptrs)
 #else
 #  error Arch not supported!
 #endif
-          
+
+#if BUILD_CONSOLE_INTERFACE
+          buflen += wnsprintfW(buffer + buflen, ArrayCount(buffer) - buflen, L"\nCreate a new issue with this report at %S.\n\n", BUILD_ISSUES_LINK_STRING_LITERAL);
+#else
+          buflen += wnsprintfW(buffer + buflen, ArrayCount(buffer) - buflen,
+              L"\nPress Ctrl+C to copy this text to clipboard, then create a new issue at\n"
+              L"<a href=\"%S\">%S</a>\n\n", BUILD_ISSUES_LINK_STRING_LITERAL, BUILD_ISSUES_LINK_STRING_LITERAL);
+#endif
+          buflen += wnsprintfW(buffer + buflen, ArrayCount(buffer) - buflen, L"Call stack:\n");
+
+          U64 frame_offset = 0;
+
+          if (frame.AddrPC.Offset == 0)
+          {
+            // if IP address is 0 then most likely we have called indirectly on NULL function pointer
+            // which means no useful stack unwinding will happen, because there's no unwind info for address 0
+            // but we can try reading 8 bytes of return address from stack, and start unwinding there
+
+            ULONG_PTR hi, lo;
+            GetCurrentThreadStackLimits(&lo, &hi);
+            if (frame.AddrStack.Offset >= lo && frame.AddrStack.Offset <= hi - sizeof(void*))
+            {
+              frame.AddrPC.Offset = *(DWORD64*)frame.AddrStack.Offset - 1;
+              frame.AddrStack.Offset += sizeof(void*);
+#if defined(_M_AMD64)
+              context->Rip = frame.AddrPC.Offset;
+              context->Rsp = frame.AddrStack.Offset;
+#elif defined(_M_ARM64)
+              context->Pc = frame.AddrPC.Offset;
+              context->Sp = frame.AddrStack.Offset;
+#endif
+            }
+
+            buflen += wnsprintfW(buffer + buflen, ArrayCount(buffer) - buflen, L"1. [NULL]\n");
+            frame_offset = 1;
+          }
+
           for(U32 idx=0; ;idx++)
           {
             const U32 max_frames = 32;
@@ -1586,19 +1626,7 @@ win32_exception_filter(EXCEPTION_POINTERS* exception_ptrs)
               break;
             }
             
-            if(idx==0)
-            {
-#if BUILD_CONSOLE_INTERFACE
-              buflen += wnsprintfW(buffer + buflen, ArrayCount(buffer) - buflen, L"\nCreate a new issue with this report at %S.\n\n", BUILD_ISSUES_LINK_STRING_LITERAL);
-#else
-              buflen += wnsprintfW(buffer + buflen, ArrayCount(buffer) - buflen,
-                                   L"\nPress Ctrl+C to copy this text to clipboard, then create a new issue at\n"
-                                   L"<a href=\"%S\">%S</a>\n\n", BUILD_ISSUES_LINK_STRING_LITERAL, BUILD_ISSUES_LINK_STRING_LITERAL);
-#endif
-              buflen += wnsprintfW(buffer + buflen, ArrayCount(buffer) - buflen, L"Call stack:\n");
-            }
-            
-            buflen += wnsprintfW(buffer + buflen, ArrayCount(buffer) - buflen, L"%u. [0x%I64x]", idx + 1, address);
+            buflen += wnsprintfW(buffer + buflen, ArrayCount(buffer) - buflen, L"%u. [0x%I64x]", frame_offset + idx + 1, address);
             
             struct {
               SYMBOL_INFOW info;