Rust DWARF debug info creates duplicate `DW_TAG_structure_type`s with the same name #52762

rocallahan · 2018-07-27T01:10:45Z

Given this pretty common pattern

enum Foo { Bar(Bar) }
struct Bar { ... }

rustc generates two DW_TAG_structure_type entries in the same namespace both called Bar, one for the Rust struct, the other for the Foo::Bar variant. This is a problem for tools that want to refer to DWARF structure types by name (e.g. when trying to guess type identities across compilation unit boundaries). It would also be a problem if a user tries to refer to the type Bar in the user interface of a debugger (without additional hacks like ignoring types containing RUST$ENUM$DISR).

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tromey · 2018-08-01T18:24:16Z

Somewhat related to bug #32924. I suspect this will be fixed by my patch for #32920, but I haven't verified it yet.

tromey · 2018-08-02T17:57:58Z

Yes, with my patch, the structure type that is generated for the enum variant is nested in the enum:

 <2><394>: Abbrev Number: 7 (DW_TAG_structure_type)
    <395>   DW_AT_name        : (indirect string, offset: 0x2cc): Foo
    <399>   DW_AT_byte_size   : 0
    <39a>   DW_AT_alignment   : 1
 <3><39b>: Abbrev Number: 8 (DW_TAG_variant_part)
 <4><39c>: Abbrev Number: 9 (DW_TAG_variant)
 <5><39d>: Abbrev Number: 10 (DW_TAG_member)
    <39e>   DW_AT_type        : <0x3a6>
    <3a2>   DW_AT_alignment   : 1
    <3a3>   DW_AT_data_member_location: 0
 <5><3a4>: Abbrev Number: 0
 <4><3a5>: Abbrev Number: 0
 <3><3a6>: Abbrev Number: 7 (DW_TAG_structure_type)
    <3a7>   DW_AT_name        : (indirect string, offset: 0x2c8): Bar
    <3ab>   DW_AT_byte_size   : 0
    <3ac>   DW_AT_alignment   : 1

The DWARF generated for Rust enums was always somewhat unusual. Rather than using DWARF constructs directly, it would emit magic field names like "RUST$ENCODED$ENUM$0$Name" and "RUST$ENUM$DISR". Since PR rust-lang#45225, though, even this has not worked -- the ad hoc scheme was not updated to handle the wider variety of niche-filling layout optimizations now available. This patch changes the generated DWARF to use the standard tags meant for this purpose; namely, DW_TAG_variant and DW_TAG_variant_part. The patch to implement this went in to LLVM 7. In order to work with older versions of LLVM, and because LLVM doesn't do anything here for PDB, the existing code is kept as a fallback mode. Support for this DWARF is in the Rust lldb and in gdb 8.2. Closes rust-lang#32920 Closes rust-lang#32924 Closes rust-lang#52762 Closes rust-lang#53153

Fix DWARF generation for enums The DWARF generated for Rust enums was always somewhat unusual. Rather than using DWARF constructs directly, it would emit magic field names like "RUST$ENCODED$ENUM$0$Name" and "RUST$ENUM$DISR". Since PR #45225, though, even this has not worked -- the ad hoc scheme was not updated to handle the wider variety of niche-filling layout optimizations now available. This patch changes the generated DWARF to use the standard tags meant for this purpose; namely, DW_TAG_variant and DW_TAG_variant_part. The patch to implement this went in to LLVM 7. In order to work with older versions of LLVM, and because LLVM doesn't do anything here for PDB, the existing code is kept as a fallback mode. Support for this DWARF is in the Rust lldb and in gdb 8.2. Closes #32920 Closes #32924 Closes #52762 Closes #53153

The DWARF generated for Rust enums was always somewhat unusual. Rather than using DWARF constructs directly, it would emit magic field names like "RUST$ENCODED$ENUM$0$Name" and "RUST$ENUM$DISR". Since PR rust-lang#45225, though, even this has not worked -- the ad hoc scheme was not updated to handle the wider variety of niche-filling layout optimizations now available. This patch changes the generated DWARF to use the standard tags meant for this purpose; namely, DW_TAG_variant and DW_TAG_variant_part. The patch to implement this went in to LLVM 7. In order to work with older versions of LLVM, and because LLVM doesn't do anything here for PDB, the existing code is kept as a fallback mode. Support for this DWARF is in the Rust lldb and in gdb 8.2. Closes rust-lang#32920 Closes rust-lang#32924 Closes rust-lang#52762 Closes rust-lang#53153

Fix DWARF generation for enums The DWARF generated for Rust enums was always somewhat unusual. Rather than using DWARF constructs directly, it would emit magic field names like "RUST$ENCODED$ENUM$0$Name" and "RUST$ENUM$DISR". Since PR #45225, though, even this has not worked -- the ad hoc scheme was not updated to handle the wider variety of niche-filling layout optimizations now available. This patch changes the generated DWARF to use the standard tags meant for this purpose; namely, DW_TAG_variant and DW_TAG_variant_part. The patch to implement this went in to LLVM 7. In order to work with older versions of LLVM, and because LLVM doesn't do anything here for PDB, the existing code is kept as a fallback mode. Support for this DWARF is in the Rust lldb and in gdb 8.2. Closes #32920 Closes #32924 Closes #52762 Closes #53153

The DWARF generated for Rust enums was always somewhat unusual. Rather than using DWARF constructs directly, it would emit magic field names like "RUST$ENCODED$ENUM$0$Name" and "RUST$ENUM$DISR". Since PR rust-lang#45225, though, even this has not worked -- the ad hoc scheme was not updated to handle the wider variety of niche-filling layout optimizations now available. This patch changes the generated DWARF to use the standard tags meant for this purpose; namely, DW_TAG_variant and DW_TAG_variant_part. The patch to implement this went in to LLVM 7. In order to work with older versions of LLVM, and because LLVM doesn't do anything here for PDB, the existing code is kept as a fallback mode. Support for this DWARF is in the Rust lldb and in gdb 8.2. Closes rust-lang#32920 Closes rust-lang#32924 Closes rust-lang#52762 Closes rust-lang#53153

Fix DWARF generation for enums The DWARF generated for Rust enums was always somewhat unusual. Rather than using DWARF constructs directly, it would emit magic field names like "RUST$ENCODED$ENUM$0$Name" and "RUST$ENUM$DISR". Since PR #45225, though, even this has not worked -- the ad hoc scheme was not updated to handle the wider variety of niche-filling layout optimizations now available. This patch changes the generated DWARF to use the standard tags meant for this purpose; namely, DW_TAG_variant and DW_TAG_variant_part. The patch to implement this went in to LLVM 7. In order to work with older versions of LLVM, and because LLVM doesn't do anything here for PDB, the existing code is kept as a fallback mode. Support for this DWARF is in the Rust lldb and in gdb 8.2. Closes #32920 Closes #32924 Closes #52762 Closes #53153

sfackler added the A-debuginfo Area: Debugging information in compiled programs (DWARF, PDB, etc.) label Jul 27, 2018

tromey mentioned this issue Sep 6, 2018

Fix DWARF generation for enums #54004

Merged

bors closed this as completed in #54004 Oct 31, 2018

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Rust DWARF debug info creates duplicate `DW_TAG_structure_type`s with the same name #52762

Rust DWARF debug info creates duplicate `DW_TAG_structure_type`s with the same name #52762

rocallahan commented Jul 27, 2018

tromey commented Aug 1, 2018

tromey commented Aug 2, 2018

Rust DWARF debug info creates duplicate DW_TAG_structure_types with the same name #52762

Rust DWARF debug info creates duplicate DW_TAG_structure_types with the same name #52762

Comments

rocallahan commented Jul 27, 2018

tromey commented Aug 1, 2018

tromey commented Aug 2, 2018

Rust DWARF debug info creates duplicate `DW_TAG_structure_type`s with the same name #52762

Rust DWARF debug info creates duplicate `DW_TAG_structure_type`s with the same name #52762