rustc_codegen_llvm: Give each codegen unit a unique DWARF name on all platforms, not just Apple ones.#92024
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platforms, not just Apple ones.
To avoid breaking split DWARF, we need to ensure that each codegen unit has a
unique `DW_AT_name`. This is because there's a remote chance that different
codegen units for the same module will have entirely identical DWARF entries
for the purpose of the DWO ID, which would violate Appendix F ("Split Dwarf
Object Files") of the DWARF 5 specification. LLVM uses the algorithm specified
in section 7.32 "Type Signature Computation" to compute the DWO ID, which does
not include any fields that would distinguish compilation units. So we must
embed the codegen unit name into the `DW_AT_name`.
Closes rust-lang#88521.
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Note that this only causes a problem in practice if an external (non-rustc) linker is used, because rustc contains some logic to merge DWARF compilation unit entries that has the side effect of working around this bug. That logic, however, is itself a workaround for some other LLVM bugs, so I think it's more appropriate to work around the problem here in rustc instead of adding Rust-specific logic to |
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Thanks for fixing this, I hadn't noticed #88521 but this explains the issue I ran into when trying to bootstrap rustc with Split DWARF (#89819 (comment)).
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📌 Commit c41fd76 has been approved by |
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rustc_codegen_llvm: Give each codegen unit a unique DWARF name on all platforms, not just Apple ones.
To avoid breaking split DWARF, we need to ensure that each codegen unit has a
unique `DW_AT_name`. This is because there's a remote chance that different
codegen units for the same module will have entirely identical DWARF entries
for the purpose of the DWO ID, which would violate Appendix F ("Split Dwarf
Object Files") of the DWARF 5 specification. LLVM uses the algorithm specified
in section 7.32 "Type Signature Computation" to compute the DWO ID, which does
not include any fields that would distinguish compilation units. So we must
embed the codegen unit name into the `DW_AT_name`.
Closes rust-lang#88521.
This was referenced Dec 17, 2021
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Dec 18, 2021
…askrgr Rollup of 7 pull requests Successful merges: - rust-lang#91566 (Apply path remapping to DW_AT_GNU_dwo_name when producing split DWARF) - rust-lang#91926 (Remove `in_band_lifetimes` from `rustc_metadata`) - rust-lang#91931 (Remove `in_band_lifetimes` from `rustc_codegen_llvm`) - rust-lang#92024 (rustc_codegen_llvm: Give each codegen unit a unique DWARF name on all platforms, not just Apple ones.) - rust-lang#92037 (Use a const ParamEnv when in default_method_body_is_const) - rust-lang#92047 (Set `RUST_BACKTRACE=0` when running location-detail tests) - rust-lang#92050 (Add a space and 2 grave accents ) Failed merges: r? `@ghost` `@rustbot` modify labels: rollup
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To avoid breaking split DWARF, we need to ensure that each codegen unit has a
unique
DW_AT_name. This is because there's a remote chance that differentcodegen units for the same module will have entirely identical DWARF entries
for the purpose of the DWO ID, which would violate Appendix F ("Split Dwarf
Object Files") of the DWARF 5 specification. LLVM uses the algorithm specified
in section 7.32 "Type Signature Computation" to compute the DWO ID, which does
not include any fields that would distinguish compilation units. So we must
embed the codegen unit name into the
DW_AT_name.Closes #88521.