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

removed in rust-lang#89597.

Also describe vtables as structs with a field for each entry.
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@michaelwoerister
michaelwoerister committed Feb 3, 2022
1 parent f4799b8 commit fc7f419
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Showing 4 changed files with 158 additions and 39 deletions.
101 changes: 90 additions & 11 deletions compiler/rustc_codegen_llvm/src/debuginfo/metadata.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -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;
Expand Down Expand Up @@ -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
Expand Down Expand Up @@ -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>,
Expand All @@ -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));

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();

type_metadata(cx, vtable_type)
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
Expand All @@ -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,
Expand Down
21 changes: 19 additions & 2 deletions compiler/rustc_codegen_ssa/src/debuginfo/type_names.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -469,7 +469,14 @@ fn push_debuginfo_type_name<'tcx>(
}
}

/// Computes a name for the global variable storing a vtable.
pub enum VTableNameKind {
// Is the name for const/static holding the vtable?
GlobalVariable,
// Is the name for the type of the vtable?
Type,
}

/// Computes a name for the global variable storing a vtable (or the type of that global variable).
///
/// The name is of the form:
///
Expand All @@ -478,10 +485,15 @@ fn push_debuginfo_type_name<'tcx>(
/// or, when generating C++-like names:
///
/// `impl$<path::to::SomeType, path::to::SomeTrait>::vtable$`
///
/// If `kind` is `VTableNameKind::Type` then the last component is `{vtable_ty}` instead of just
/// `{vtable}`, so that the type and the corresponding global variable get assigned different
/// names.
pub fn compute_debuginfo_vtable_name<'tcx>(
tcx: TyCtxt<'tcx>,
t: Ty<'tcx>,
trait_ref: Option<ty::PolyExistentialTraitRef<'tcx>>,
kind: VTableNameKind,
) -> String {
let cpp_like_debuginfo = cpp_like_debuginfo(tcx);

Expand Down Expand Up @@ -514,7 +526,12 @@ pub fn compute_debuginfo_vtable_name<'tcx>(

push_close_angle_bracket(cpp_like_debuginfo, &mut vtable_name);

let suffix = if cpp_like_debuginfo { "::vtable$" } else { "::{vtable}" };
let suffix = match (cpp_like_debuginfo, kind) {
(true, VTableNameKind::GlobalVariable) => "::vtable$",
(false, VTableNameKind::GlobalVariable) => "::{vtable}",
(true, VTableNameKind::Type) => "::vtable_type$",
(false, VTableNameKind::Type) => "::{vtable_type}",
};

vtable_name.reserve_exact(suffix.len());
vtable_name.push_str(suffix);
Expand Down
35 changes: 30 additions & 5 deletions src/test/codegen/debug-vtable.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -9,19 +9,41 @@
// compile-flags: -Cdebuginfo=2 -Copt-level=0 -Csymbol-mangling-version=v0
// ignore-tidy-linelength

// NONMSVC: ![[USIZE:[0-9]+]] = !DIBasicType(name: "usize"
// MSVC: ![[USIZE:[0-9]+]] = !DIDerivedType(tag: DW_TAG_typedef, name: "usize"
// NONMSVC: ![[PTR:[0-9]+]] = !DIDerivedType(tag: DW_TAG_pointer_type, name: "*const ()"
// MSVC: ![[PTR:[0-9]+]] = !DIDerivedType(tag: DW_TAG_pointer_type, name: "ptr_const$<tuple$<> >"

// NONMSVC: !DIGlobalVariable(name: "<debug_vtable::Foo as debug_vtable::SomeTrait>::{vtable}"
// MSVC: !DIGlobalVariable(name: "impl$<debug_vtable::Foo, debug_vtable::SomeTrait>::vtable$"
// NONMSVC: !DIDerivedType(tag: DW_TAG_pointer_type, name: "*const ()",
// MSVC: !DIDerivedType(tag: DW_TAG_pointer_type, name: "ptr_const$<tuple$<> >",
// CHECK: !DISubrange(count: 5

// NONMSVC: ![[VTABLE_TY0:[0-9]+]] = !DICompositeType(tag: DW_TAG_structure_type, name: "<debug_vtable::Foo as debug_vtable::SomeTrait>::{vtable_type}", {{.*}} size: {{320|160}}, align: {{64|32}}, flags: DIFlagArtificial, {{.*}} vtableHolder: ![[FOO_TYPE:[0-9]+]],
// MSVC: ![[VTABLE_TY0:[0-9]+]] = !DICompositeType(tag: DW_TAG_structure_type, name: "impl$<debug_vtable::Foo, debug_vtable::SomeTrait>::vtable_type$", {{.*}} size: {{320|160}}, align: {{64|32}}, flags: DIFlagArtificial, {{.*}} vtableHolder: ![[FOO_TYPE:[0-9]+]],
// CHECK: !DIDerivedType(tag: DW_TAG_member, name: "drop_in_place", scope: ![[VTABLE_TY0]], {{.*}} baseType: ![[PTR]], size: {{64|32}}, align: {{64|32}})
// CHECK: !DIDerivedType(tag: DW_TAG_member, name: "size", scope: ![[VTABLE_TY0]], {{.*}} baseType: ![[USIZE]], size: {{64|32}}, align: {{64|32}}, offset: {{64|32}})
// CHECK: !DIDerivedType(tag: DW_TAG_member, name: "align", scope: ![[VTABLE_TY0]], {{.*}} baseType: ![[USIZE]], size: {{64|32}}, align: {{64|32}}, offset: {{128|64}})
// CHECK: !DIDerivedType(tag: DW_TAG_member, name: "__method3", scope: ![[VTABLE_TY0]], {{.*}} baseType: ![[PTR]], size: {{64|32}}, align: {{64|32}}, offset: {{192|96}})
// CHECK: !DIDerivedType(tag: DW_TAG_member, name: "__method4", scope: ![[VTABLE_TY0]], {{.*}} baseType: ![[PTR]], size: {{64|32}}, align: {{64|32}}, offset: {{256|128}})
// CHECK: ![[FOO_TYPE]] = !DICompositeType(tag: DW_TAG_structure_type, name: "Foo",

// NONMSVC: !DIGlobalVariable(name: "<debug_vtable::Foo as debug_vtable::SomeTraitWithGenerics<u64, i8>>::{vtable}"
// MSVC: !DIGlobalVariable(name: "impl$<debug_vtable::Foo, debug_vtable::SomeTraitWithGenerics<u64,i8> >::vtable$"
// CHECK: !DISubrange(count: 4

// NONMSVC: ![[VTABLE_TY1:[0-9]+]] = !DICompositeType(tag: DW_TAG_structure_type, name: "<debug_vtable::Foo as debug_vtable::SomeTraitWithGenerics<u64, i8>>::{vtable_type}", {{.*}}, size: {{256|128}}, align: {{64|32}}, flags: DIFlagArtificial, {{.*}}, vtableHolder: ![[FOO_TYPE]],
// MSVC: ![[VTABLE_TY1:[0-9]+]] = !DICompositeType(tag: DW_TAG_structure_type, name: "impl$<debug_vtable::Foo, debug_vtable::SomeTraitWithGenerics<u64,i8> >::vtable_type$", {{.*}}, size: {{256|128}}, align: {{64|32}}, flags: DIFlagArtificial, {{.*}}, vtableHolder: ![[FOO_TYPE]],
// CHECK: !DIDerivedType(tag: DW_TAG_member, name: "drop_in_place", scope: ![[VTABLE_TY1]], {{.*}} baseType: ![[PTR]], size: {{64|32}}, align: {{64|32}})
// CHECK: !DIDerivedType(tag: DW_TAG_member, name: "size", scope: ![[VTABLE_TY1]], {{.*}} baseType: ![[USIZE]], size: {{64|32}}, align: {{64|32}}, offset: {{64|32}})
// CHECK: !DIDerivedType(tag: DW_TAG_member, name: "align", scope: ![[VTABLE_TY1]], {{.*}} baseType: ![[USIZE]], size: {{64|32}}, align: {{64|32}}, offset: {{128|64}})
// CHECK: !DIDerivedType(tag: DW_TAG_member, name: "__method3", scope: ![[VTABLE_TY1]], {{.*}} baseType: ![[PTR]], size: {{64|32}}, align: {{64|32}}, offset: {{192|96}})

// NONMSVC: !DIGlobalVariable(name: "<debug_vtable::Foo as _>::{vtable}"
// MSVC: !DIGlobalVariable(name: "impl$<debug_vtable::Foo, _>::vtable$"
// CHECK: !DISubrange(count: 3

// NONMSVC: ![[VTABLE_TY2:[0-9]+]] = !DICompositeType(tag: DW_TAG_structure_type, name: "<debug_vtable::Foo as _>::{vtable_type}", {{.*}}, size: {{192|96}}, align: {{64|32}}, flags: DIFlagArtificial, {{.*}}, vtableHolder: ![[FOO_TYPE]],
// MSVC: ![[VTABLE_TY2:[0-9]+]] = !DICompositeType(tag: DW_TAG_structure_type, name: "impl$<debug_vtable::Foo, _>::vtable_type$", {{.*}}, size: {{192|96}}, align: {{64|32}}, flags: DIFlagArtificial, {{.*}}, vtableHolder: ![[FOO_TYPE]],
// CHECK: !DIDerivedType(tag: DW_TAG_member, name: "drop_in_place", scope: ![[VTABLE_TY2]], {{.*}}, baseType: ![[PTR]], size: {{64|32}}, align: {{64|32}})
// CHECK: !DIDerivedType(tag: DW_TAG_member, name: "size", scope: ![[VTABLE_TY2]], {{.*}}, baseType: ![[USIZE]], size: {{64|32}}, align: {{64|32}}, offset: {{64|32}})
// CHECK: !DIDerivedType(tag: DW_TAG_member, name: "align", scope: ![[VTABLE_TY2]], {{.*}}, baseType: ![[USIZE]], size: {{64|32}}, align: {{64|32}}, offset: {{128|64}})

// NONMSVC: !DIGlobalVariable(name: "<debug_vtable::bar::{closure_env#0} as core::ops::function::FnOnce<(core::option::Option<&dyn core::ops::function::Fn<(), Output=()>>)>>::{vtable}"
// MSVC: !DIGlobalVariable(name: "impl$<debug_vtable::bar::closure_env$0, core::ops::function::FnOnce<tuple$<enum$<core::option::Option<ref$<dyn$<core::ops::function::Fn<tuple$<>,assoc$<Output,tuple$<> > > > > >, {{.*}}, {{.*}}, Some> > > >::vtable$"
Expand All @@ -34,6 +56,9 @@

#![crate_type = "lib"]

// Force emission for debuginfo for usize and *const() early..
pub static mut XYZ: Option<(usize, *const ())> = None;

pub struct Foo;

pub trait SomeTrait {
Expand Down
40 changes: 19 additions & 21 deletions src/test/codegen/debuginfo-generic-closure-env-names.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -17,35 +17,34 @@

// compile-flags: -Cdebuginfo=2 --edition 2021 -Copt-level=0 -Csymbol-mangling-version=v0


// CHECK: [[non_generic_closure_NAMESPACE:!.*]] = !DINamespace(name: "non_generic_closure"
// CHECK: [[function_containing_closure_NAMESPACE:!.*]] = !DINamespace(name: "function_containing_closure"
// CHECK: [[generic_async_function_NAMESPACE:!.*]] = !DINamespace(name: "generic_async_function"
// CHECK: [[generic_async_block_NAMESPACE:!.*]] = !DINamespace(name: "generic_async_block"

// non_generic_closure()
// NONMSVC: !DICompositeType(tag: DW_TAG_structure_type, name: "{closure_env#0}", scope: [[non_generic_closure_NAMESPACE]]
// MSVC: !DICompositeType(tag: DW_TAG_structure_type, name: "closure_env$0", scope: [[non_generic_closure_NAMESPACE]]
// NONMSVC: !DICompositeType(tag: DW_TAG_structure_type, name: "{closure_env#0}", scope: ![[non_generic_closure_NAMESPACE:[0-9]+]],
// MSVC: !DICompositeType(tag: DW_TAG_structure_type, name: "closure_env$0", scope: ![[non_generic_closure_NAMESPACE:[0-9]+]],
// CHECK: ![[non_generic_closure_NAMESPACE]] = !DINamespace(name: "non_generic_closure"

// CHECK: ![[function_containing_closure_NAMESPACE:[0-9]+]] = !DINamespace(name: "function_containing_closure"
// CHECK: ![[generic_async_function_NAMESPACE:[0-9]+]] = !DINamespace(name: "generic_async_function"
// CHECK: ![[generic_async_block_NAMESPACE:[0-9]+]] = !DINamespace(name: "generic_async_block"

// function_containing_closure<u32>()
// NONMSVC: !DICompositeType(tag: DW_TAG_structure_type, name: "{closure_env#0}<u32>", scope: [[function_containing_closure_NAMESPACE]]
// MSVC: !DICompositeType(tag: DW_TAG_structure_type, name: "closure_env$0<u32>", scope: [[function_containing_closure_NAMESPACE]]
// NONMSVC: !DICompositeType(tag: DW_TAG_structure_type, name: "{closure_env#0}<u32>", scope: ![[function_containing_closure_NAMESPACE]]
// MSVC: !DICompositeType(tag: DW_TAG_structure_type, name: "closure_env$0<u32>", scope: ![[function_containing_closure_NAMESPACE]]

// generic_async_function<Foo>()
// NONMSVC: !DICompositeType(tag: DW_TAG_structure_type, name: "{async_fn_env#0}<debuginfo_generic_closure_env_names::Foo>", scope: [[generic_async_function_NAMESPACE]]
// NONMSVC: !DICompositeType(tag: DW_TAG_structure_type, name: "{async_fn_env#0}<debuginfo_generic_closure_env_names::Foo>", scope: ![[generic_async_function_NAMESPACE]]

// generic_async_function<u32>()
// NONMSVC: !DICompositeType(tag: DW_TAG_structure_type, name: "{async_fn_env#0}<u32>", scope: [[generic_async_function_NAMESPACE]]
// NONMSVC: !DICompositeType(tag: DW_TAG_structure_type, name: "{async_fn_env#0}<u32>", scope: ![[generic_async_function_NAMESPACE]]

// generic_async_block<Foo>()
// NONMSVC: !DICompositeType(tag: DW_TAG_structure_type, name: "{async_block_env#0}<debuginfo_generic_closure_env_names::Foo>", scope: [[generic_async_block_NAMESPACE]]
// NONMSVC: !DICompositeType(tag: DW_TAG_structure_type, name: "{async_block_env#0}<debuginfo_generic_closure_env_names::Foo>", scope: ![[generic_async_block_NAMESPACE]]

// generic_async_block<u32>()
// NONMSVC: !DICompositeType(tag: DW_TAG_structure_type, name: "{async_block_env#0}<u32>", scope: [[generic_async_block_NAMESPACE]]
// NONMSVC: !DICompositeType(tag: DW_TAG_structure_type, name: "{async_block_env#0}<u32>", scope: ![[generic_async_block_NAMESPACE]]

// function_containing_closure<Foo>()
// NONMSVC: !DICompositeType(tag: DW_TAG_structure_type, name: "{closure_env#0}<debuginfo_generic_closure_env_names::Foo>", scope: [[function_containing_closure_NAMESPACE]]
// MSVC: !DICompositeType(tag: DW_TAG_structure_type, name: "closure_env$0<debuginfo_generic_closure_env_names::Foo>", scope: [[function_containing_closure_NAMESPACE]]
// NONMSVC: !DICompositeType(tag: DW_TAG_structure_type, name: "{closure_env#0}<debuginfo_generic_closure_env_names::Foo>", scope: ![[function_containing_closure_NAMESPACE]]
// MSVC: !DICompositeType(tag: DW_TAG_structure_type, name: "closure_env$0<debuginfo_generic_closure_env_names::Foo>", scope: ![[function_containing_closure_NAMESPACE]]


#![crate_type = "lib"]
Expand All @@ -54,15 +53,14 @@ use std::future::Future;
pub struct Foo;

pub fn non_generic_closure(x: Foo) -> Box<dyn FnOnce() -> Foo> {
// This static only exists to trigger generating the namespace debuginfo for
// `function_containing_closure` at a predictable, early point, which makes
// writing the FileCheck tests above simpler.
static _X: u8 = 0;
return Box::new(move || x);
}

fn function_containing_closure<T: 'static>(x: T) -> impl FnOnce() -> T {
static _X: u8 = 0; // Same as above
// This static only exists to trigger generating the namespace debuginfo for
// `function_containing_closure` at a predictable, early point, which makes
// writing the FileCheck tests above simpler.
static _X: u8 = 0;

return move || x;
}
Expand Down

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