Module link 

Finding a linker and telling it what to link.

Design: spec/04-driver-and-cli.md section 4.9. There is no linker of our own before 1.0, so this finds one on the machine and builds the command line it wants.

The linker is invoked directly rather than through the system compiler driver. Going through cc would be shorter to write and would borrow that compiler’s idea of where everything is, and it would also mean this compiler cannot link on a machine that has no other compiler on it, which is most of the machines a compiler ends up on. It would also make -### output a line that does not say what happens, since the interesting half would be inside the program being spawned.

What is not decided here

The startup files and the library directories are looked for rather than configured, for the same reason library looks for the headers: gcc settles this when it is built because a gcc is built for the machine it will run on, and this is one binary that runs wherever it is copied. So the shape of the answer is a list of candidates per platform of which the ones that exist are taken, and a cross build says where the rest is with --sysroot.

What is not here yet

crtbegin and crtend, and -lgcc. Those are a compiler’s own runtime rather than the library’s, and this compiler’s is rucc-builtins, which is not written. A program that needs neither links and runs without them, which is every program that does not divide a 128-bit integer or unwind through a frame, and a program that needs one gets an undefined symbol from the linker naming exactly what is missing rather than a wrong answer at run time.

Darwin and Windows. ld64 wants a different line, a platform version load command and a different set of default libraries, and link.exe wants another one again. Each arrives with the target that needs it.

Structs

LinkOptions

What the command line said about linking.

Linker

A linker, found.

Enums

Error

Why a link could not be run.

Item

One item on the link line, in the order it was written, because link order is semantic.

Functions

candidates

Where the library’s own files might be, in search order.

find

The linker to use, looked for where a linker is.

line

What the linker is told, in order, not counting the linker itself.

order

The names to look for, in the order section 4.9 gives.

render

The whole invocation as one line, quoted the way -### prints it.

run

Runs the linker and waits for it.