Emit correct ELF symbol types for data in NativeAOT objects

[max-charlamb]

Summary

ElfObjectWriter.EmitSymbolTable classified every defined symbol purely by size:

definition.Size > 0 ? STT_FUNC : STT_NOTYPE;

This produced two wrong results for data symbols:

1. Vtables emitted as STT_NOTYPE. A MethodTable/EEType symbol points at a non-zero offset within its node (the EEType sits after the GCDesc), so Size == 0 and it became STT_NOTYPE. Released lldb only infers a type for NOTYPE symbols whose section name is in a hard-coded list (.text/.data/.rodata/.bss); symbols in other allocated sections such as .hydrated (the NOBITS region that rehydrated data structures live in when data dehydration is enabled) stay untyped and are not surfaced in lldb symbol lookup. Tools that read st_info directly (gdb, nm, addr2line, perf) never see a type at all.
2. Data emitted as STT_FUNC. Data symbols with Size > 0 in .rodata/.data were marked STT_FUNC, i.e. data mislabeled as code (lldb then treats them as functions).

Fix

Classify by section kind instead of size:

(section.SectionHeader.Flags & SHF_TLS) == SHF_TLS ? STT_TLS :
(section.SectionHeader.Flags & SHF_EXECINSTR) != SHF_EXECINSTR ? STT_OBJECT :
definition.Size > 0 ? STT_FUNC : STT_NOTYPE;

Non-executable sections emit STT_OBJECT; executable sections keep the existing STT_FUNC/STT_NOTYPE behavior unchanged. This matches the canonical typing every other ELF producer uses and is size-neutral (only the st_info type byte changes).

Validation

Cross-emitted a Linux x64 object (--targetos:linux, dehydration on) before/after the change from an otherwise identical toolchain. Object size is byte-identical (3,555,456 bytes).

Section	Before	After
.hydrated (NOBITS, vtables)	1084 NOTYPE + 377 FUNC	1461 OBJECT
.rodata	245 FUNC (+2 NOTYPE)	247 OBJECT
.data	338 FUNC	338 OBJECT
.text (code)	83 FUNC	83 FUNC (unchanged)

Executable-section symbols are untouched, so ARM/AArch64/RISC-V mapping symbols ($a/$d/$x) and trampolines are unaffected.

Note

This PR description was generated with the assistance of GitHub Copilot.

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Pull request overview

This PR updates NativeAOT’s ELF object writer symbol-table emission to choose ELF symbol types based on section flags (TLS / executable vs non-executable), rather than inferring type from symbol size alone.

Changes:

• Adjust symbol classification in ElfObjectWriter.EmitSymbolTable to emit STT_OBJECT for defined symbols in non-executable sections.
• Preserve existing STT_FUNC/STT_NOTYPE behavior for executable sections and keep STT_TLS for TLS sections.

[Copilot]

Pull request overview

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