Add x86_64-unknown-vibix.json target spec and xtask integration

[dburkart]

Summary

• Create x86_64-unknown-vibix.json custom target spec per RFC 0009, enabling cargo +nightly -Z build-std cross-compilation for vibix userspace
• Add [target.x86_64-unknown-vibix] rustflags section in .cargo/config.toml
• Add cargo xtask validate-target subcommand that parses and validates the target spec against RFC-mandated fields/values
• Wire VIBIX_USERSPACE_TARGET constant in xtask for downstream build commands

Test plan

• cargo xtask build — kernel build unaffected, passes cleanly
• cargo xtask validate-target — parses JSON, confirms all required fields present and correct

Closes #850

🤖 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: 99c612c7-b32f-4ba7-add6-03f1ef330657

📥 Commits

Reviewing files that changed from the base of the PR and between 752e61e and 0d793f1.

📒 Files selected for processing (1)

• xtask/src/main.rs

✅ Files skipped from review due to trivial changes (1)

• xtask/src/main.rs

---

📝 Walkthrough

Walkthrough

Adds a new Rust target spec x86_64-unknown-vibix (JSON + .cargo config) and a new xtask CLI validate-target subcommand that parses and validates the target JSON fields.

Changes

Vibix Target Specification and Validation

Layer / File(s)	Summary
Target Specification x86_64-unknown-vibix.json	New LLVM/Rust target spec for x86_64-unknown-vibix: triple, data layout, endianness, pointer/C widths, panic-strategy: "abort", disable-redzone: true, features: "+sse,+sse2", has-thread-local, tls-model: "initial-exec", relocation-model: "static", position-independent-executables: false, linker-flavor: "gnu-lld", linker: "rust-lld", pre-link-args including -nostdlib/-static, and crt-objects-fallback: false.
Build Configuration .cargo/config.toml	Adds [target.x86_64-unknown-vibix] block with rustflags = ["-C relocation-model=static", "-C no-redzone=yes", "-C force-frame-pointers=yes"] for userspace builds.
Validation Tool — deps xtask/Cargo.toml	Adds serde_json = "1" dependency for JSON parsing in xtask.
Validation Tool — implementation xtask/src/main.rs	Adds VIBIX_USERSPACE_TARGET constant; new validate-target subcommand and validate_vibix_target() which reads x86_64-unknown-vibix.json, requires the root JSON be an object, checks presence and exact expected values for multiple string fields (most), ensures has-thread-local / disable-redzone are true and position-independent-executables is false, aggregates validation errors, and prints a success mark on pass.
CLI wiring / help xtask/src/main.rs	Registers validate-target in the CLI dispatch and updates usage banner.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Possibly related issues

• #852: The new target spec and xtask validation directly support end-to-end std-on-vibix testing for userspace builds.
• #858: The x86_64-unknown-vibix target and cargo config enable building pjdfstest and other userspace tests for the vibix target.

Possibly related PRs

• dburkart/vibix#689: Modifies xtask/src/main.rs with new xtask subcommands; related CLI-area changes.
• dburkart/vibix#847: RFC and docs for Rust std on vibix; this PR implements the target spec referenced there.
• dburkart/vibix#611: Adds xtask subcommands and updates dispatcher logic, touching the same xtask CLI surface.

Poem

🐰 I found a JSON nook today,
fields aligned in tidy play,
rustflags snug, the linker hums,
xtask checks, the green tick comes,
vibix userspace hops away. 🥕

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Linked Issues check	⚠️ Warning	The PR partially implements issue #850 but omits two key requirements: integrating into xtask build pipeline (build-userspace command) and updating ext2_image.rs.	Complete the remaining tasks: add 'cargo xtask build-userspace' command and update ext2_image.rs to install userspace binaries into the ext2 rootfs image.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately describes the primary changes: adding a custom target spec file and xtask integration.
Description check	✅ Passed	The description clearly explains the changes, references the RFC, mentions the specific files modified, and provides a test plan.
Out of Scope Changes check	✅ Passed	All changes are directly related to the custom target spec implementation and xtask integration as specified in issue #850.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ 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 m850-target-spec

---

_{Comment @coderabbitai help to get the list of available commands and usage tips.}

[coderabbitai]

🧹 Nitpick comments (2)

xtask/src/main.rs (2)

3499-3509: 💤 Low value

Consider validating static-position-independent-executables.

The target spec includes static-position-independent-executables: false, but this field isn't validated. If it's mandated by RFC 0009, consider adding it to the boolean-must-be-false check.

Proposed addition

     // Boolean fields that must be false.
-    for key in ["position-independent-executables"] {
+    for key in ["position-independent-executables", "static-position-independent-executables"] {
         match obj.get(key) {

🤖 Prompt for 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.

In `@xtask/src/main.rs` around lines 3499 - 3509, The boolean-field validation
currently iterates over ["position-independent-executables"] and ensures each
obj.get(key) is present and false; add "static-position-independent-executables"
to that list so the same logic (obj.get(key) match, errors.push(...) on missing,
and errors.push(...) if val.as_bool() != Some(false)) applies to the
static-position-independent-executables field as required by RFC 0009.

---

3474-3481: 💤 Low value

Type mismatch produces a misleading error message.

If a field has the wrong JSON type (e.g., boolean instead of string), as_str().unwrap_or("") returns "", producing an error like expected "x86_64", got "" rather than indicating a type mismatch. This is minor since the spec is internally authored.

🤖 Prompt for 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.

In `@xtask/src/main.rs` around lines 3474 - 3481, The comparison currently uses
let actual = val.as_str().unwrap_or("") which hides type mismatches (producing
an empty string) — change the block around expected_val/val to explicitly check
for a string: if let Some(actual) = val.as_str() { compare actual == expected
and push the existing errors.push message } else { push a clear type-mismatch
error via errors.push that reports either the actual JSON value
(format!("{val}")) or its type (e.g., using val.is_* checks or format!("{:?}",
val)) so callers see "expected string, got boolean" (reference symbols:
expected_val, val, actual, errors.push).

🤖 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.

Nitpick comments:
In `@xtask/src/main.rs`:
- Around line 3499-3509: The boolean-field validation currently iterates over
["position-independent-executables"] and ensures each obj.get(key) is present
and false; add "static-position-independent-executables" to that list so the
same logic (obj.get(key) match, errors.push(...) on missing, and
errors.push(...) if val.as_bool() != Some(false)) applies to the
static-position-independent-executables field as required by RFC 0009.
- Around line 3474-3481: The comparison currently uses let actual =
val.as_str().unwrap_or("") which hides type mismatches (producing an empty
string) — change the block around expected_val/val to explicitly check for a
string: if let Some(actual) = val.as_str() { compare actual == expected and push
the existing errors.push message } else { push a clear type-mismatch error via
errors.push that reports either the actual JSON value (format!("{val}")) or its
type (e.g., using val.is_* checks or format!("{:?}", val)) so callers see
"expected string, got boolean" (reference symbols: expected_val, val, actual,
errors.push).

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 5a2bc7fe-d0f1-4fbb-aa5f-683a86554b6a

📥 Commits

Reviewing files that changed from the base of the PR and between fc1f2b9 and 752e61e.

📒 Files selected for processing (4)

• .cargo/config.toml
• x86_64-unknown-vibix.json
• xtask/Cargo.toml
• xtask/src/main.rs