Add built in PSP target

[overdrivenpotato]

This adds a new target, mipsel-sony-psp, corresponding to the Sony PSP. The linker script is necessary to handle special sections, which are required by the target. This has been tested with my rust-psp crate and I can confirm it works as intended.

The linker script is taken from here. It has been slightly adapted to work with rust and LLD.

The stdarch submodule was also updated in order for libcore to build successfully.

[rust-highfive]

r? @cramertj

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[rust-highfive]

⚠️ Warning ⚠️

• These commits modify submodules.

[jonas-schievink]

Won't this leave the created file around after every compilation?

[overdrivenpotato]

Yes, though it’s continuously overwritten in a temporary directory. Is there a better way to do this?

[jonas-schievink]

Using an OS-managed tempfile that is deleted automatically could work better here.

Or, if you're fine with having to tell Cargo to pass the linker script, you don't have to build it into the compiler at all (this is what the embedded ecosystem does, but there you tend to customize linker scripts a lot, so it's not quite the same situation).

[overdrivenpotato]

The linker script is never really customized on this platform, so ideally it's built into the compiler like this. The main role of this script is to handle special sections, of which there is a small fixed set. This is used for things like specifying the module entry point and specifying imports.

How would you go about using an OS-managed temporary file? I don't see anything in std, is there something I missed? Or perhaps is it better to add a crates.io dependency for this?

[jonas-schievink]

tempfile should do the trick, and we already pull it in as a dependency. In fact we already use it to create a directory to store temporary artifacts in, so you can probably reuse that somehow, but it might involve some plumbing.

[overdrivenpotato]

Unfortunately it looks like neither tempfile::tempfile() nor tempfile::tempdir() will work. The tempdir() function returns a handle which deletes the directory when dropped, so unfortunately it will be deleted after the Target struct is returned. tempfile::tempfile() has a similar problem - after writing to the file, the File instance will be dropped which closes the last handle to the file, and thus deleting the script.

Maybe there is a pool where I can store either of these instances until after the linker is run? This seems ugly though. The tempfile crate stores files in the env::temp_dir() location anyways.

[jonas-schievink]

If you want to add first-class support for target-specific linker scripts, the place to do that would probably be here. You can fetch it from the target spec and store it in tmpdir.

[overdrivenpotato]

Thanks for the link! I’ll give that a shot

[crlf0710]

r? @hanna-kruppe

[hanna-kruppe]

r? @jonas-schievink since they're on it already and I have little time for Rust at the moment.

[overdrivenpotato]

I've added an lld_link_script field to TargetOptions, for LLD scripts embedded in the target. How does that look?

[jonas-schievink]

Looks pretty good!

[overdrivenpotato]

I rewrote the link script from scratch. I believe this absolves any licensing issues, given that it is a clean room implementation. The lines linking the eh_frame sections are taken directly from LLVM here, they were not present in the original PSPSDK script.

[jonas-schievink]

Ah this also works. Thanks!

@bors r+

[bors]

📌 Commit 425723f has been approved by jonas-schievink