Fix

Move unwinder == NULL check before unwinder->debug_offsets.code_object.co_tlbc to prevent null pointer dereference.

The Bug

// Line 435 - Before (buggy):
if (ctx->tlbc_index == 0 || unwinder->debug_offsets.code_object.co_tlbc == 0 || unwinder == NULL)

C short-circuit evaluation means unwinder->debug_offsets (position 2) is dereferenced BEFORE unwinder == NULL (position 3) is checked. The NULL check is dead code — it can never protect against a NULL unwinder because the crash happens first.

The Fix

// Line 435 - After (fixed):
if (ctx->tlbc_index == 0 || unwinder == NULL || unwinder->debug_offsets.code_object.co_tlbc == 0)

Context

The code already shows awareness that unwinder can be NULL:

• Line 359: if (unwinder && ...) — proper NULL check exists elsewhere
• The NULL check at line 435 proves the developer intended it to be nullable

Affected Versions

• Python 3.13t+ (free-threading builds)
• Python 3.14t+ (free-threading builds)
• Only affects Py_GIL_DISABLED builds

Closes #149953

• Issue: NULL pointer dereference in _remote_debugging code_objects.c:435 (dead null check) #149953