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Rollup merge of #95270 - michaelwoerister:fix-box-unsized-debuginfo, r=wesleywiser

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debuginfo: Fix debuginfo for Box<T> where T is unsized.

Before this fix, the debuginfo for the fields was generated from the struct defintion of Box<T>, but (at least at the moment) the compiler pretends that Box<T> is just a (fat) pointer, so the fields need to be `pointer` and `vtable` instead of `__0: Unique<T>` and `__1: Allocator`.

This is meant as a temporary mitigation until we can make sure that simply treating Box as a regular struct in debuginfo does not cause too much breakage in the ecosystem.

r? ````@wesleywiser````
This commit is contained in:
Dylan DPC 2022-03-25 01:34:31 +01:00 committed by GitHub
commit e039dc813b
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2 changed files with 33 additions and 5 deletions
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19
compiler/rustc_codegen_llvm/src/debuginfo/metadata.rs
View File

@ -166,6 +166,13 @@ fn build_pointer_or_reference_di_node<'ll, 'tcx>(
pointee_type: Ty<'tcx>,
unique_type_id: UniqueTypeId<'tcx>,
) -> DINodeCreationResult<'ll> {
// The debuginfo generated by this function is only valid if `ptr_type` is really just
// a (fat) pointer. Make sure it is not called for e.g. `Box<T, NonZSTAllocator>`.
debug_assert_eq!(
cx.size_and_align_of(ptr_type),
cx.size_and_align_of(cx.tcx.mk_mut_ptr(pointee_type))
);
let pointee_type_di_node = type_di_node(cx, pointee_type);
return_if_di_node_created_in_meantime!(cx, unique_type_id);
@ -212,7 +219,17 @@ fn build_pointer_or_reference_di_node<'ll, 'tcx>(
DIFlags::FlagZero,
),
|cx, owner| {
let layout = cx.layout_of(ptr_type);
// FIXME: If this fat pointer is a `Box` then we don't want to use its
// type layout and instead use the layout of the raw pointer inside
// of it.
// The proper way to handle this is to not treat Box as a pointer
// at all and instead emit regular struct debuginfo for it. We just
// need to make sure that we don't break existing debuginfo consumers
// by doing that (at least not without a warning period).
let layout_type =
if ptr_type.is_box() { cx.tcx.mk_mut_ptr(pointee_type) } else { ptr_type };
let layout = cx.layout_of(layout_type);
let addr_field = layout.field(cx, abi::FAT_PTR_ADDR);
let extra_field = layout.field(cx, abi::FAT_PTR_EXTRA);

19
src/test/debuginfo/unsized.rs
View File

@ -16,13 +16,17 @@
// gdbg-check:$3 = {pointer = [...], vtable = [...]}
// gdbr-check:$3 = &unsized::Foo<dyn core::fmt::Debug> {pointer: [...], vtable: [...]}
// gdb-command:print _box
// gdbg-check:$4 = {pointer = [...], vtable = [...]}
// gdbr-check:$4 = alloc::boxed::Box<unsized::Foo<dyn core::fmt::Debug>, alloc::alloc::Global> {pointer: [...], vtable: [...]}
// gdb-command:print tuple_slice
// gdbg-check:$4 = {data_ptr = [...], length = 2}
// gdbr-check:$4 = &(i32, i32, [i32]) {data_ptr: [...], length: 2}
// gdbg-check:$5 = {data_ptr = [...], length = 2}
// gdbr-check:$5 = &(i32, i32, [i32]) {data_ptr: [...], length: 2}
// gdb-command:print tuple_dyn
// gdbg-check:$5 = {pointer = [...], vtable = [...]}
// gdbr-check:$5 = &(i32, i32, dyn core::fmt::Debug) {pointer: [...], vtable: [...]}
// gdbg-check:$6 = {pointer = [...], vtable = [...]}
// gdbr-check:$6 = &(i32, i32, dyn core::fmt::Debug) {pointer: [...], vtable: [...]}
// === CDB TESTS ===================================================================================
@ -42,6 +46,12 @@
// cdb-check: [+0x000] pointer : 0x[...] [Type: unsized::Foo<dyn$<core::fmt::Debug> > *]
// cdb-check: [...] vtable : 0x[...] [Type: unsigned [...]int[...] (*)[3]]
// cdb-command:dx _box
// cdb-check:
// cdb-check:_box [Type: alloc::boxed::Box<unsized::Foo<dyn$<core::fmt::Debug> >,alloc::alloc::Global>]
// cdb-check:[+0x000] pointer : 0x[...] [Type: unsized::Foo<dyn$<core::fmt::Debug> > *]
// cdb-check:[...] vtable : 0x[...] [Type: unsigned [...]int[...] (*)[3]]
// cdb-command:dx tuple_slice
// cdb-check:tuple_slice [Type: ref$<tuple$<i32,i32,slice$<i32> > >]
// cdb-check: [+0x000] data_ptr : 0x[...] [Type: tuple$<i32,i32,slice$<i32> > *]
@ -69,6 +79,7 @@ fn main() {
let a: &Foo<[u8]> = &foo.value;
let b: &Foo<Foo<[u8]>> = &foo;
let c: &Foo<dyn std::fmt::Debug> = &Foo { value: 7i32 };
let _box: Box<Foo<dyn std::fmt::Debug>> = Box::new(Foo { value: 8i32 });
// Also check unsized tuples
let tuple_slice: &(i32, i32, [i32]) = &(0, 1, [2, 3]);