preserve input section alignment

[katsyoshi]

Summary

• preserve each input section's alignment while merging .text, .rodata, and .data
• emit NOP padding for .text and zero padding for .rodata and .data
• account for the synthetic _start prefix when aligning the first input .text contribution
• propagate the maximum input sh_addralign and include padding in symbol and relocation offsets
• apply aligned .data offsets to .rela.data relocations
• distinguish defined entry-point symbols from undefined _start references
• align the load bias for sections whose alignment exceeds the default load bias
• add assembler fixtures plus Builder, Layout, and end-to-end integration coverage

Testing

• bundle exec rake test — 58 tests, 260 assertions, 0 failures, 0 errors, 1 environment-dependent omission
• bundle exec rake steep:check — no type errors

Manual testing

• linked and ran an executable containing an 8 MiB-aligned .text section
• confirmed that the output virtual address satisfies the section alignment while preserving the entry-point offset

The integration test links the aligned contributions with the self linker and verifies that the resulting executable exits with status 42.

[katsyoshi]

@codex review

[chatgpt-codex-connector]

💡 Codex Review

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Reviewed commit: d91a455177

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[katsyoshi]

@codex review

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: dba0061a9e

ℹ️ About Codex in GitHub

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[katsyoshi]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. Another round soon, please!

Reviewed commit: f61943dbc5

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".