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Guillaume Gomez
0846622465
Add uwtable annotation to modules when required When unwind tables are enabled with `-Cforce-unwind-tables=y`, Rust will annotate all functions with the `uwtable` annotation. However, this annotation is missing on modules, which leads to incorrect unwind tables being generated by LLVM for constructors (such as `asan.module_ctor`). This was discovered because it leads to a crash in Linux when KASAN and dynamic shadow call stack are both enabled. In this scenario, the kernel uses the unwind tables to locate the `paciasp` and `autiasp` instructions in each function and patches the machine code at boot to use the shadow call stack instructions instead. However, LLVM's AArch64PointerAuth pass emits DWARF info for `paciasp` whenever `-g` is passed, but only emits DWARF info for `autiasp` when the `uwtable` attribute is present. Since the `uwtable` annotation is missing for modules, the relevant directives are generated for only the `autiasp` instruction in `asan.module_ctor`, and not for the `paciasp` instruction. This causes the kernel's dynamic SCS logic to patch the prolouge of `asan.module_ctor`, but not the epilogue. This leads to a crash as the shadow call stack becomes unbalanced. The fact that LLVM doesn't use the same condition for whether to emit DWARF information for both instructions may be a separate bug in LLVM. Relevant issue: https://github.com/llvm/llvm-project/issues/188234 AI assistance was used to determine the root cause of this crash from the observed symptoms, and to write the tests. Also thanks to @samitolvanen and @maurer for debugging this issue. Similar to this previous PR of mine: rust-lang/rust#130824