From 5bda42e4dec9106fb310c30178c1283ff92ebfa2 Mon Sep 17 00:00:00 2001
From: Alan Wu <XrXr@users.noreply.github.com>
Date: Tue, 14 Oct 2025 21:45:10 -0400
Subject: [PATCH] ZJIT: Include GC object dump when seeing dead objects

Strictly more info than just the builtin_type from `assert_ne!`.

Old:

    assertion `left != right` failed: ZJIT should only see live objects
      left: 0
     right: 0

New:

    ZJIT saw a dead object. T_type=0, out-of-heap:0x0000000110d4bb40

Also, the new `VALUE::obj_info` is more flexible for print debugging than the
dump_info() it replaces. It now allows you to use it as part of a `format!`
string instead of always printing to stderr for you.
---
 zjit/bindgen/src/main.rs       |  2 +-
 zjit/src/cruby.rs              | 32 ++++++++++++++++++++++++++------
 zjit/src/cruby_bindings.inc.rs |  6 +++++-
 3 files changed, 32 insertions(+), 8 deletions(-)

diff --git a/zjit/bindgen/src/main.rs b/zjit/bindgen/src/main.rs
index b40986c0f6..975a2d9157 100644
--- a/zjit/bindgen/src/main.rs
+++ b/zjit/bindgen/src/main.rs
@@ -82,7 +82,7 @@ fn main() {
         .allowlist_type("ruby_rstring_flags")
 
         // This function prints info about a value and is useful for debugging
-        .allowlist_function("rb_obj_info_dump")
+        .allowlist_function("rb_raw_obj_info")
 
         .allowlist_function("ruby_init")
         .allowlist_function("ruby_init_stack")
diff --git a/zjit/src/cruby.rs b/zjit/src/cruby.rs
index 1f514787f1..1a2dce03ed 100644
--- a/zjit/src/cruby.rs
+++ b/zjit/src/cruby.rs
@@ -90,7 +90,7 @@
 
 use std::convert::From;
 use std::ffi::{c_void, CString, CStr};
-use std::fmt::{Debug, Formatter};
+use std::fmt::{Debug, Display, Formatter};
 use std::os::raw::{c_char, c_int, c_uint};
 use std::panic::{catch_unwind, UnwindSafe};
 
@@ -400,10 +400,27 @@ pub enum ClassRelationship {
     NoRelation,
 }
 
+/// A print adapator for debug info about a [VALUE]. Includes info
+/// the GC knows about the handle. Example: `println!("{}", value.obj_info());`.
+pub struct ObjInfoPrinter(VALUE);
+
+impl Display for ObjInfoPrinter {
+    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
+        use std::mem::MaybeUninit;
+        const BUFFER_SIZE: usize = 0x100;
+        let mut buffer: MaybeUninit<[c_char; BUFFER_SIZE]> = MaybeUninit::uninit();
+        let info = unsafe {
+            rb_raw_obj_info(buffer.as_mut_ptr().cast(), BUFFER_SIZE, self.0);
+            CStr::from_ptr(buffer.as_ptr().cast()).to_string_lossy()
+        };
+        write!(f, "{info}")
+    }
+}
+
 impl VALUE {
-    /// Dump info about the value to the console similarly to rp(VALUE)
-    pub fn dump_info(self) {
-        unsafe { rb_obj_info_dump(self) }
+    /// Get a printer for raw debug info from `rb_obj_info()` about the value.
+    pub fn obj_info(self) -> ObjInfoPrinter {
+        ObjInfoPrinter(self)
     }
 
     /// Return whether the value is truthy or falsy in Ruby -- only nil and false are falsy.
@@ -507,8 +524,11 @@ impl VALUE {
     pub fn class_of(self) -> VALUE {
         if !self.special_const_p() {
             let builtin_type = self.builtin_type();
-            assert_ne!(builtin_type, RUBY_T_NONE, "ZJIT should only see live objects");
-            assert_ne!(builtin_type, RUBY_T_MOVED, "ZJIT should only see live objects");
+            assert!(
+                builtin_type != RUBY_T_NONE && builtin_type != RUBY_T_MOVED,
+                "ZJIT saw a dead object. T_type={builtin_type}, {}",
+                self.obj_info()
+            );
         }
 
         unsafe { rb_yarv_class_of(self) }
diff --git a/zjit/src/cruby_bindings.inc.rs b/zjit/src/cruby_bindings.inc.rs
index 56b569e064..f18c0035ee 100644
--- a/zjit/src/cruby_bindings.inc.rs
+++ b/zjit/src/cruby_bindings.inc.rs
@@ -839,7 +839,6 @@ unsafe extern "C" {
     pub fn rb_ivar_set(obj: VALUE, name: ID, val: VALUE) -> VALUE;
     pub fn rb_ivar_defined(obj: VALUE, name: ID) -> VALUE;
     pub fn rb_attr_get(obj: VALUE, name: ID) -> VALUE;
-    pub fn rb_obj_info_dump(obj: VALUE);
     pub fn rb_class_allocate_instance(klass: VALUE) -> VALUE;
     pub fn rb_obj_equal(obj1: VALUE, obj2: VALUE) -> VALUE;
     pub fn rb_reg_new_ary(ary: VALUE, options: ::std::os::raw::c_int) -> VALUE;
@@ -872,6 +871,11 @@ unsafe extern "C" {
         cfp: *const rb_control_frame_t,
     ) -> *const rb_callable_method_entry_t;
     pub fn rb_obj_info(obj: VALUE) -> *const ::std::os::raw::c_char;
+    pub fn rb_raw_obj_info(
+        buff: *mut ::std::os::raw::c_char,
+        buff_size: usize,
+        obj: VALUE,
+    ) -> *const ::std::os::raw::c_char;
     pub fn rb_ec_stack_check(ec: *mut rb_execution_context_struct) -> ::std::os::raw::c_int;
     pub fn rb_gc_writebarrier_remember(obj: VALUE);
     pub fn rb_shape_id_offset() -> i32;