ZJIT: Avoid binding to rb_iseq_constant_body

Its definition changes depending on e.g. whether there is YJIT in the
build.

zjit.c

@@ -31,6 +31,10 @@
 
 #include <errno.h>
 
+enum zjit_struct_offsets {
+    ISEQ_BODY_OFFSET_PARAM = offsetof(struct rb_iseq_constant_body, param)
+};
+
 #define PTR2NUM(x) (rb_int2inum((intptr_t)(void *)(x)))
 
 // For a given raw_sample (frame), set the hash with the caller's

zjit/bindgen/src/main.rs

@@ -301,6 +301,7 @@ fn main() {
         .allowlist_function("rb_zjit_defined_ivar")
         .allowlist_function("rb_zjit_insn_leaf")
         .allowlist_type("jit_bindgen_constants")
+        .allowlist_type("zjit_struct_offsets")
         .allowlist_function("rb_assert_holding_vm_lock")
         .allowlist_function("rb_jit_shape_too_complex_p")
         .allowlist_function("rb_jit_multi_ractor_p")
@@ -428,6 +429,7 @@ fn main() {
         // We define these manually, don't import them
         .blocklist_type("VALUE")
         .blocklist_type("ID")
+        .blocklist_type("rb_iseq_constant_body")
 
         // Avoid binding to stuff we don't use
         .blocklist_item("rb_thread_struct.*")

zjit/src/cruby.rs

@@ -231,6 +231,16 @@ pub fn insn_len(opcode: usize) -> u32 {
     }
 }
 
+/// We avoid using bindgen for `rb_iseq_constant_body` since its definition changes depending
+/// on build configuration while we need one bindgen file that works for all configurations.
+/// Use an opaque type for it instead.
+/// See: <https://doc.rust-lang.org/nomicon/ffi.html#representing-opaque-structs>
+#[repr(C)]
+pub struct rb_iseq_constant_body {
+    _data: [u8; 0],
+    _marker: core::marker::PhantomData<(*mut u8, core::marker::PhantomPinned)>,
+}
+
 /// An object handle similar to VALUE in the C code. Our methods assume
 /// that this is a handle. Sometimes the C code briefly uses VALUE as
 /// an unsigned integer type and don't necessarily store valid handles but
@@ -683,7 +693,8 @@ pub trait IseqAccess {
 impl IseqAccess for IseqPtr {
     /// Get a description of the ISEQ's signature. Analogous to `ISEQ_BODY(iseq)->param` in C.
     unsafe fn params<'a>(self) -> &'a IseqParameters {
-        unsafe { &(*(*self).body).param }
+        use crate::cast::IntoUsize;
+        unsafe { &*((*self).body.byte_add(ISEQ_BODY_OFFSET_PARAM.to_usize()) as *const IseqParameters) }
     }
 }
 

zjit/src/cruby_bindings.inc.rs

@@ -595,40 +595,6 @@ pub type rb_jit_func_t = ::std::option::Option<
     ) -> VALUE,
 >;
 #[repr(C)]
-pub struct rb_iseq_constant_body {
-    pub type_: rb_iseq_type,
-    pub iseq_size: ::std::os::raw::c_uint,
-    pub iseq_encoded: *mut VALUE,
-    pub param: rb_iseq_constant_body_rb_iseq_parameters,
-    pub location: rb_iseq_location_t,
-    pub insns_info: rb_iseq_constant_body_iseq_insn_info,
-    pub local_table: *const ID,
-    pub lvar_states: *mut rb_iseq_constant_body_lvar_state,
-    pub catch_table: *mut iseq_catch_table,
-    pub parent_iseq: *const rb_iseq_struct,
-    pub local_iseq: *mut rb_iseq_struct,
-    pub is_entries: *mut iseq_inline_storage_entry,
-    pub call_data: *mut rb_call_data,
-    pub variable: rb_iseq_constant_body__bindgen_ty_1,
-    pub local_table_size: ::std::os::raw::c_uint,
-    pub ic_size: ::std::os::raw::c_uint,
-    pub ise_size: ::std::os::raw::c_uint,
-    pub ivc_size: ::std::os::raw::c_uint,
-    pub icvarc_size: ::std::os::raw::c_uint,
-    pub ci_size: ::std::os::raw::c_uint,
-    pub stack_max: ::std::os::raw::c_uint,
-    pub builtin_attrs: ::std::os::raw::c_uint,
-    pub prism: bool,
-    pub mark_bits: rb_iseq_constant_body__bindgen_ty_2,
-    pub outer_variables: *mut rb_id_table,
-    pub mandatory_only_iseq: *const rb_iseq_t,
-    pub jit_entry: rb_jit_func_t,
-    pub jit_entry_calls: ::std::os::raw::c_ulong,
-    pub jit_exception: rb_jit_func_t,
-    pub jit_exception_calls: ::std::os::raw::c_ulong,
-    pub zjit_payload: *mut ::std::os::raw::c_void,
-}
-#[repr(C)]
 #[derive(Debug, Copy, Clone)]
 pub struct rb_iseq_constant_body_rb_iseq_parameters {
     pub flags: rb_iseq_constant_body_rb_iseq_parameters__bindgen_ty_1,
@@ -1866,6 +1832,8 @@ pub const DEFINED_REF: defined_type = 15;
 pub const DEFINED_FUNC: defined_type = 16;
 pub const DEFINED_CONST_FROM: defined_type = 17;
 pub type defined_type = u32;
+pub const ISEQ_BODY_OFFSET_PARAM: zjit_struct_offsets = 16;
+pub type zjit_struct_offsets = u32;
 pub const ROBJECT_OFFSET_AS_HEAP_FIELDS: jit_bindgen_constants = 16;
 pub const ROBJECT_OFFSET_AS_ARY: jit_bindgen_constants = 16;
 pub const RUBY_OFFSET_RSTRING_LEN: jit_bindgen_constants = 16;