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debuginfo: Bring back DW_AT_containing_type for vtables after it has accidentally been

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removed in https://github.com/rust-lang/rust/pull/89597.

Also describe vtables as structs with a field for each entry.
This commit is contained in:
Michael Woerister 2022-01-25 14:34:34 +01:00
parent f4799b8709
commit fc7f419a63
4 changed files with 158 additions and 39 deletions
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101
compiler/rustc_codegen_llvm/src/debuginfo/metadata.rs
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@ -21,6 +21,7 @@ use crate::value::Value;
use cstr::cstr;
use rustc_codegen_ssa::debuginfo::type_names::cpp_like_debuginfo;
use rustc_codegen_ssa::debuginfo::type_names::VTableNameKind;
use rustc_codegen_ssa::traits::*;
use rustc_data_structures::fingerprint::Fingerprint;
use rustc_data_structures::fx::FxHashMap;
@ -276,6 +277,12 @@ impl<'ll, 'tcx> TypeMap<'ll, 'tcx> {
) -> String {
format!("{}_variant_part", self.get_unique_type_id_as_string(enum_type_id))
}
/// Gets the `UniqueTypeId` for the type of a vtable.
fn get_unique_type_id_of_vtable_type(&mut self, vtable_type_name: &str) -> UniqueTypeId {
let interner_key = self.unique_id_interner.intern(vtable_type_name);
interner_key
}
}
/// A description of some recursive type. It can either be already finished (as
@ -2586,6 +2593,14 @@ pub fn create_global_var_metadata<'ll>(cx: &CodegenCx<'ll, '_>, def_id: DefId, g
}
/// Generates LLVM debuginfo for a vtable.
///
/// The vtable type looks like a struct with a field for each function pointer and super-trait
/// pointer it contains (plus the `size` and `align` fields).
///
/// Except for `size`, `align`, and `drop_in_place`, the field names don't try to mirror
/// the name of the method they implement. This can be implemented in the future once there
/// is a proper disambiguation scheme for dealing with methods from different traits that have
/// the same name.
fn vtable_type_metadata<'ll, 'tcx>(
cx: &CodegenCx<'ll, 'tcx>,
ty: Ty<'tcx>,
@ -2602,16 +2617,79 @@ fn vtable_type_metadata<'ll, 'tcx>(
COMMON_VTABLE_ENTRIES
};
// FIXME: We describe the vtable as an array of *const () pointers. The length of the array is
// correct - but we could create a more accurate description, e.g. by describing it
// as a struct where each field has a name that corresponds to the name of the method
// it points to.
// However, this is not entirely straightforward because there might be multiple
// methods with the same name if the vtable is for multiple traits. So for now we keep
// things simple instead of adding some ad-hoc disambiguation scheme.
let vtable_type = tcx.mk_array(tcx.mk_imm_ptr(tcx.types.unit), vtable_entries.len() as u64);
// All function pointers are described as opaque pointers. This could be improved in the future
// by describing them as actual function pointers.
let void_pointer_ty = tcx.mk_imm_ptr(tcx.types.unit);
let void_pointer_type_debuginfo = type_metadata(cx, void_pointer_ty);
let usize_debuginfo = type_metadata(cx, tcx.types.usize);
let (pointer_size, pointer_align) = cx.size_and_align_of(void_pointer_ty);
// If `usize` is not pointer-sized and -aligned then the size and alignment computations
// for the vtable as a whole would be wrong. Let's make sure this holds even on weird
// platforms.
assert_eq!(cx.size_and_align_of(tcx.types.usize), (pointer_size, pointer_align));
type_metadata(cx, vtable_type)
let vtable_type_name =
compute_debuginfo_vtable_name(cx.tcx, ty, poly_trait_ref, VTableNameKind::Type);
let unique_type_id = debug_context(cx)
.type_map
.borrow_mut()
.get_unique_type_id_of_vtable_type(&vtable_type_name);
let size = pointer_size * vtable_entries.len() as u64;
// This gets mapped to a DW_AT_containing_type attribute which allows GDB to correlate
// the vtable to the type it is for.
let vtable_holder = type_metadata(cx, ty);
let vtable_type_metadata = create_struct_stub(
cx,
size,
pointer_align,
&vtable_type_name,
unique_type_id,
NO_SCOPE_METADATA,
DIFlags::FlagArtificial,
Some(vtable_holder),
);
// Create a field for each entry in the vtable.
let fields: Vec<_> = vtable_entries
.iter()
.enumerate()
.filter_map(|(index, vtable_entry)| {
let (field_name, field_type) = match vtable_entry {
ty::VtblEntry::MetadataDropInPlace => {
("drop_in_place".to_string(), void_pointer_type_debuginfo)
}
ty::VtblEntry::Method(_) => {
// Note: This code does not try to give a proper name to each method
// because their might be multiple methods with the same name
// (coming from different traits).
(format!("__method{}", index), void_pointer_type_debuginfo)
}
ty::VtblEntry::TraitVPtr(_) => {
(format!("__super_trait_ptr{}", index), void_pointer_type_debuginfo)
}
ty::VtblEntry::MetadataAlign => ("align".to_string(), usize_debuginfo),
ty::VtblEntry::MetadataSize => ("size".to_string(), usize_debuginfo),
ty::VtblEntry::Vacant => return None,
};
Some(MemberDescription {
name: field_name,
type_metadata: field_type,
offset: pointer_size * index as u64,
size: pointer_size,
align: pointer_align,
flags: DIFlags::FlagZero,
discriminant: None,
source_info: None,
})
})
.collect();
let type_params = create_DIArray(DIB(cx), &[]);
set_members_of_composite_type(cx, vtable_type_metadata, fields, None, type_params);
vtable_type_metadata
}
/// Creates debug information for the given vtable, which is for the
@ -2633,11 +2711,12 @@ pub fn create_vtable_metadata<'ll, 'tcx>(
return;
}
let vtable_name = compute_debuginfo_vtable_name(cx.tcx, ty, poly_trait_ref);
let vtable_name =
compute_debuginfo_vtable_name(cx.tcx, ty, poly_trait_ref, VTableNameKind::GlobalVariable);
let vtable_type = vtable_type_metadata(cx, ty, poly_trait_ref);
let linkage_name = "";
unsafe {
let linkage_name = "";
llvm::LLVMRustDIBuilderCreateStaticVariable(
DIB(cx),
NO_SCOPE_METADATA,