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scripts: verify rust/libmacros.so ELF architecture compatibility - #872
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When building the bcachefs DKMS module on a system where Rust is enabled, rustc dynamically loads the procedural macro shared library (rust/libmacros.so) directly into its host process at compile time. If kernel headers or prebuilt kernel artifacts were compiled on a host with a different architecture (e.g. cross-compiled on x86_64 and installed on an aarch64 system), rustc on the target host cannot load the alien libmacros.so. This causes the DKMS build to fall back to the C-only module. Add an ELF architecture compatibility check to rust-is-available-dkms.sh: - Add helper function elf_arch_name() to map ELF class, endianness, and e_machine bytes to human-readable architecture names (x86_64, aarch64, arm, riscv, etc.). - Inspect the ELF header of a native host binary ($HOSTRUSTC, $RUSTC, or /bin/sh) using od and compare its class, endianness, and machine type against rust/libmacros.so. - If a mismatch is found, trigger skip() with a clear diagnostic: "host architecture ($host_arch) does not match rust/libmacros.so ($macro_arch); native kernel headers required" This allows DKMS to catch cross-architecture header mismatches early and gracefully fall back to building the C-only bcachefs module while logging the exact reason in the build log. # Conflicts: # fs/scripts/rust-is-available-dkms.sh
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Summary
Adds an ELF architecture compatibility check for
rust/libmacros.soto the DKMS Rust availability script (rust-is-available-dkms.sh).Problem
When building out-of-tree Rust modules via DKMS,
rustcdynamically loads procedural macro shared libraries (rust/libmacros.so) directly into its host process at compile time viadlopen().If kernel headers or prebuilt kernel artifacts were cross-compiled on a different host architecture (e.g., compiled on
x86_64and installed on anaarch64target system), hostrustccannot load the foreign.so. This causes DKMS builds to fail deep insiderustcwith cryptic dynamic linking or crate loading errors (E0463).This test catches architecture mismatches early and gracefully falls back to building the C-only module, logging the exact cause in the DKMS build log.
Implementation Details
get_elf_arch(): Reads the first 20 bytes of an ELF header in a single POSIXodcall, extracting ELF class, endianness, ande_machine(x86_64,aarch64,arm,riscv,loongarch64, etc.).get_host_arch(): Reusesget_elf_arch()on native host binaries ($HOSTRUSTC,$RUSTC,$CC, or/bin/sh). This guarantees 1:1 string parity between the running toolchain andlibmacros.so, preventing false positives on 32-bit platforms (armvsarmv7l) or in chroot/container environments.$host_arch != $macro_arch),skip()is triggered with a clear diagnostic: