Pretty printing debuginfo for size-optimized enums is broken #53153
Labels
A-debuginfo
Area: Debugging information in compiled programs (DWARF, PDB, etc.)
C-bug
Category: This is a bug.
T-compiler
Relevant to the compiler team, which will review and decide on the PR/issue.
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michaelwoerister
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A-debuginfo
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You might as well assign this to me, along with the other enum debuginfo bugs. I'm working on those as quickly as I can; though since we've normally considered lldb a prerequisite, and that is going somewhat slowly (see PR #52716 for the gory details), it may yet be a while. |
tromey
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Sep 21, 2018
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
bors
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Sep 23, 2018
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
tromey
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Oct 1, 2018
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
bors
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Oct 1, 2018
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
tromey
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Oct 30, 2018
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
bors
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Oct 30, 2018
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
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The code that generates the special DWARF field names for size-optimized enums is broken for a while now. PRs keep getting opened to "fix" this on the pretty printer side but that's not possible because the debuginfo does not contain the necessary information for the pretty printer to correctly decode a given value. See #51777 (comment) for an example and some discussion on a possible fix.
This will be fixed eventually when enums get a proper representation in DWARF. Meanwhile, it's unclear how much of a priority fixing this is.
cc @tromey
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