Add vibix_abi crate with syscall macro, GlobalAlloc, errno, and stdio

[dburkart]

Summary

• Create the vibix_abi userspace crate (#![no_std], no external deps) that bridges Rust's std PAL to vibix syscalls (Phase 1, Step 2 of RFC 0009)
• Implements syscall!() macro with proper x86_64 clobber registers (issue repro-fork harness runs ~15,000 cycles per boot in CI — every soak iteration hits HARD_CAP #531)
• Implements GlobalAlloc using brk for small allocations, mmap for large (>= 128 KiB)
• Implements thread-local errno via #[thread_local] static (relies on TLS from epic Epic: x86_64 static TLS (ELF variant II) for std-on-vibix #827)
• Implements write_stdout/write_stderr using writev syscall (nr 20)
• Adds crate to workspace Cargo.toml

Closes #849

Test plan

• cargo build -p vibix_abi compiles cleanly
• cargo xtask build passes (full kernel + userspace build)

🤖 Generated with Claude Code

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 11f3141c-2ab2-4812-bc7f-ad982c24722f

📥 Commits

Reviewing files that changed from the base of the PR and between 71589c9 and 856d9f0.

📒 Files selected for processing (1)

• userspace/vibix_abi/src/alloc.rs

🚧 Files skipped from review as they are similar to previous changes (1)

• userspace/vibix_abi/src/alloc.rs

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📝 Walkthrough

Walkthrough

A new vibix_abi crate is added to the workspace, providing a Rust ABI bridge between std and vibix syscalls. It includes raw x86_64 syscall wrappers (macro + funcs), a GlobalAlloc using brk/mmap, thread-local errno with __errno_location, and stdio helpers for stdout/stderr.

Changes

vibix_abi Crate Creation

Layer / File(s)	Summary
Workspace Setup Cargo.toml	Added "userspace/vibix_abi" to workspace members.
Crate Configuration userspace/vibix_abi/Cargo.toml	New crate manifest with package metadata and [lib] target at src/lib.rs.
Crate Root & Exports userspace/vibix_abi/src/lib.rs	#![no_std], #![feature(thread_local)], and pub mod exports: alloc, errno, stdio, syscall.
Syscall Foundation userspace/vibix_abi/src/syscall.rs	Adds #[macro_export] syscall! and pub unsafe fn syscall0–syscall6 implemented with x86_64 inline syscall asm, returning i64 and declaring clobbers.
Standard I/O userspace/vibix_abi/src/stdio.rs	Implements IoVec, internal writev helper, and write_stdout/write_stderr using syscall3 (writev).
Memory Allocator userspace/vibix_abi/src/alloc.rs	Adds VibixAllocator implementing GlobalAlloc: small allocations use a brk-backed bump allocator (BRK_CURRENT atomic), large allocations (≥128 KiB) use anonymous mmap; munmap used on dealloc for large regions.
Errno TLS userspace/vibix_abi/src/errno.rs	Defines #[thread_local] static ERRNO: Cell<i32> and exports #[no_mangle] extern "C" fn __errno_location() -> *mut i32.

Sequence Diagram(s)

sequenceDiagram
    participant App as Application
    participant ABI as vibix_abi (syscall / stdio)
    participant Kernel as Kernel
    App->>ABI: call write_stdout(buf)
    ABI->>ABI: build IoVec, syscall3(SYS_WRITEV, fd, &iov, 1)
    ABI->>Kernel: syscall writev(fd, iov, 1)
    Kernel-->>ABI: return bytes_or_errno
    ABI-->>App: return i64 result

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sequenceDiagram
    participant AllocUser as Allocating code
    participant Alloc as VibixAllocator
    participant ABI as vibix_abi (syscall)
    participant Kernel as Kernel
    AllocUser->>Alloc: request alloc(layout)
    alt size < 128KiB
        Alloc->>ABI: syscall brk(new_brk)
        ABI->>Kernel: syscall brk
        Kernel-->>ABI: return brk_ptr_or_failure
        ABI-->>Alloc: brk result
        Alloc-->>AllocUser: pointer (bump)
    else size >= 128KiB or brk failure
        Alloc->>ABI: syscall mmap(size, PROT, MAP_ANON|MAP_PRIVATE)
        ABI->>Kernel: syscall mmap
        Kernel-->>ABI: return mmap_ptr_or_MAP_FAILED
        ABI-->>Alloc: mmap result
        Alloc-->>AllocUser: pointer or null
    end

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Estimated code review effort

🎯 4 (Complex) | ⏱️ ~45 minutes

Possibly related issues

• Implement sys/fs/vibix.rs and sys/process/vibix.rs in the std fork #854: vibix_abi provides raw syscall wrappers and stdio used by kernel-side sys/fs/vibix implementations.
• Create vibix_libc crate and fork libc crate for vibix type definitions #855: overlaps with low-level primitives (syscall, __errno_location) expected by vibix_libc.
• Fork std and add vibix PAL with stdio support; build with -Z build-std #851: implements VibixAllocator and stdio symbols targeted by the std PAL wiring.

Possibly related PRs

• dburkart/vibix#532: Related x86_64 syscall asm clobbering adjustments that complement this crate's syscall asm.
• dburkart/vibix#861: Kernel-side syscall handlers (writev, readv, etc.) that match the userspace interface added here.
• dburkart/vibix#847: RFC proposing the vibix_abi PAL shim implemented by this PR.

Poem

🐰 I nibble syscalls, stitch them neat,
brk and mmap make cozy seats,
errno hums in thread-local tune,
stdout hops beneath the moon,
a tiny crate — a giant leap!

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely summarizes the main changes: adding a new vibix_abi crate with its key components (syscall macro, GlobalAlloc, errno, and stdio).
Description check	✅ Passed	The description is well-detailed and directly related to the changeset, explaining the purpose, implementation details, and test results for the vibix_abi crate.
Linked Issues check	✅ Passed	The PR successfully implements all core coding requirements from issue #849: syscall macro with x86_64 assembly [#531, #849], GlobalAlloc with brk/mmap [#849], thread-local errno [#827, #849], and stdio wrappers [#849]. Minor planned items (clock_gettime, getrandom) are deferred as noted.
Out of Scope Changes check	✅ Passed	All changes are directly scoped to creating the vibix_abi crate and integrating it into the workspace; no unrelated modifications or scope creep detected.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.

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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch m849-vibix-abi

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@userspace/vibix_abi/src/alloc.rs`:
- Around line 64-67: The allocator leaks small blocks when sbrk/brk growth
fails: alloc() falls back to mmap_alloc() when result < new_brk but dealloc()
only munmap() when size >= MMAP_THRESHOLD; fix by recording allocation source in
the mmap'd block and checking that in dealloc(): modify mmap_alloc() to
over-allocate a small header (e.g., a magic/flag and stored size) and return a
pointer after the header, and update dealloc() to inspect that header (or its
magic) to decide to call munmap() and use the stored size for munmap length;
keep MMAP_THRESHOLD logic for common cases but use the header presence as the
authoritative signal for mmap'ed blocks (symbols: alloc, dealloc, mmap_alloc,
MMAP_THRESHOLD).

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 802cfacb-91aa-456e-8e7a-626a727b7268

📥 Commits

Reviewing files that changed from the base of the PR and between 451b6a1 and 71589c9.

📒 Files selected for processing (7)

• Cargo.toml
• userspace/vibix_abi/Cargo.toml
• userspace/vibix_abi/src/alloc.rs
• userspace/vibix_abi/src/errno.rs
• userspace/vibix_abi/src/lib.rs
• userspace/vibix_abi/src/stdio.rs
• userspace/vibix_abi/src/syscall.rs