Claude review: gpu: nova-core: export Rust symbols for dependent modules

[Claude Code Review Bot <claude-review@example.com>]

Patch Review

This is the core workaround. The approach:

1. Use `nm -p --defined-only` to extract global text symbols starting with `_R` (Rust v0 mangling prefix)
2. Generate `extern void sym(void); EXPORT_SYMBOL_GPL(sym);` for each
3. Compile the generated header into `nova_core_exports.o`

```makefile
rust_exports = \
    $(NM) -p --defined-only $(1) | \
    awk '$$2 == "T" && $$3 ~ /^_R/ { \
        printf "extern void %s(void); EXPORT_SYMBOL_GPL(%s);\n", $$3, $$3 \
    }'
```

**Observations:**

- Filtering on `$$2 == "T"` (global text) and `$$3 ~ /^_R/` is correct for Rust v0 mangled symbols. This won't accidentally pick up C symbols.
- The `extern void sym(void)` declarations are technically type-incorrect (the actual functions have different signatures), but this is only used for `EXPORT_SYMBOL_GPL()` which just needs the symbol address. This is the same pattern used elsewhere in the kernel for cross-language symbol exports.
- Using `filechk` ensures the header is regenerated when the object changes.
- `nova_core_exports.c` is clean and minimal.

**Potential concern:** This exports *all* global Rust text symbols from `nova_core.o`, not just the ones `nova-drm` actually needs. This is a broad export surface. The cover letter acknowledges this is a workaround, so this is acceptable for now, but a comment noting that a more targeted approach would be preferable long-term might be useful.

**No blocking issues.**

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Generated by Claude Code Patch Reviewer