Rust -Zextra-link-arg Test

This repo provides an example of how -Zextra-link-arg can work in Rust.

It consists of three packages:

• lib-maybe-link: A library that may or may not set linker flags
• without-linker: Uses lib-maybe-link without requesting linker flags
• attempt-linker: Uses lib-maybe-link with linker flags

Usage

Install an embedded target that supports linker flags. For example:

rustup +nightly target add riscv32imac-unknown-none-elf

Next, build without-linker, and observe how it builds:

[10:15:54 AM] D:/Code/linker-test> cargo +nightly -Zextra-link-arg build -p without-linker --target riscv32imac-unknown-none-elf
   Compiling lib-maybe-link v0.1.0 (D:\Code\linker-test\lib-maybe-link)
   Compiling without-linker v0.1.0 (D:\Code\linker-test\without-linker)
    Finished dev [unoptimized + debuginfo] target(s) in 0.51s
[10:15:57 AM] D:/Code/linker-test>

Attempt to build attempt-linker, and observe that it fails because it's picked up the nonexistent linker flag:

[10:21:50 AM] D:/Code/linker-test> cargo +nightly -Zextra-link-arg build -p attempt-linker --target riscv32imac-unknown-none-elf
   Compiling lib-maybe-link v0.1.0 (D:\Code\linker-test\lib-maybe-link)
   Compiling attempt-linker v0.1.0 (D:\Code\linker-test\attempt-linker)
error: linking with `rust-lld` failed: exit code: 1
  |
  = note: "rust-lld" "-flavor" "gnu" "-L" "C:\\Users\\smcro\\.rustup\\toolchains\\nightly-x86_64-pc-windows-gnu\\lib\\rustlib\\riscv32imac-unknown-none-elf\\lib" "D:\\Code\\linker-test\\target\\riscv32imac-unknown-none-elf\\debug\\deps\\attempt_linker-e325983111c6bb57.35ff07kpanugha7m.rcgu.o" "-o" "D:\\Code\\linker-test\\target\\riscv32imac-unknown-none-elf\\debug\\deps\\attempt_linker-e325983111c6bb57" "--gc-sections" "-L" "D:\\Code\\linker-test\\target\\riscv32imac-unknown-none-elf\\debug\\deps" "-L" "D:\\Code\\linker-test\\target\\debug\\deps" "-L" "C:\\Users\\smcro\\.rustup\\toolchains\\nightly-x86_64-pc-windows-gnu\\lib\\rustlib\\riscv32imac-unknown-none-elf\\lib" "-Bstatic" "D:\\Code\\linker-test\\target\\riscv32imac-unknown-none-elf\\debug\\deps\\liblib_maybe_link-7e3515822fca08dd.rlib" "C:\\Users\\smcro\\.rustup\\toolchains\\nightly-x86_64-pc-windows-gnu\\lib\\rustlib\\riscv32imac-unknown-none-elf\\lib\\librustc_std_workspace_core-f8dea4d885a94b85.rlib" "C:\\Users\\smcro\\.rustup\\toolchains\\nightly-x86_64-pc-windows-gnu\\lib\\rustlib\\riscv32imac-unknown-none-elf\\lib\\libcore-39eb6a0559508a94.rlib" "C:\\Users\\smcro\\.rustup\\toolchains\\nightly-x86_64-pc-windows-gnu\\lib\\rustlib\\riscv32imac-unknown-none-elf\\lib\\libcompiler_builtins-ce3fc8c77ec9a399.rlib" "--passing-args-does-work" "-Bdynamic"
  = note: rust-lld: error: unknown argument '--passing-args-does-work'


error: aborting due to previous error

error: could not compile `attempt-linker`

To learn more, run the command again with --verbose.
[10:22:07 AM] D:/Code/linker-test>

Finally, build without-linker and observe that the change to the maybe-link library feature flags don't force a rebuild:

[10:16:48 AM] D:/Code/linker-test> cargo +nightly -Zextra-link-arg build -p without-linker --target riscv32imac-unknown-none-elf
    Finished dev [unoptimized + debuginfo] target(s) in 0.02s
[10:17:42 AM] D:/Code/linker-test>