feat: CoW fork stacks, demand-paged stack growth, blocking pipe reads#185
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feat: CoW fork stacks, demand-paged stack growth, blocking pipe reads#185
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Replace fork's redundant stack allocation/copy with CoW sharing — the parent's stack pages are already CoW-mapped by setup_cow_pages(), so the child can reuse them directly. This makes fork significantly faster and removes the CHILD_STACK_SIZE hack entirely. Add demand-paged stack growth: when userspace touches memory just below the current stack bottom, the page fault handler allocates and maps new pages on demand (up to 2MB MAX_USER_STACK_SIZE), eliminating the need to pre-allocate large stacks. The faster CoW fork exposed a latent race condition where parents would read from pipes before children had written, getting EAGAIN. Implement proper blocking pipe reads following the existing FIFO blocking pattern (register waiter, block thread, HLT loop, retry on wake). Also: suppress ELF loader debug logging (→ trace level) that was flooding serial output, fix test binary paths to match ext2 layout, rebuild ext2 image with all userspace binaries, fix exec_from_ext2_test expected exit code to match hello_std_real. All 252 boot stages pass. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
The ARM64 CI branch had temporarily removed x86_64 testing from boot-tests.yml. Add back the x86_64 boot-stages (252 tests) and kthread-stress jobs so both architectures are tested on every PR. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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Summary
setup_cow_pages(), so children reuse them directly. EliminatesCHILD_STACK_SIZEhack entirely.MAX_USER_STACK_SIZE) when userspace touches memory below the current stack bottom.Test plan
cargo build --releasewith zero warnings🤖 Generated with Claude Code