Roc linker library base setup

Cargo.lock

@@ -2219,6 +2219,16 @@ dependencies = [
  "memchr",
 ]
 
+[[package]]
+name = "object"
+version = "0.26.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c55827317fb4c08822499848a14237d2874d6f139828893017237e7ab93eb386"
+dependencies = [
+ "flate2",
+ "memchr",
+]
+
 [[package]]
 name = "once_cell"
 version = "1.7.2"
@@ -3296,6 +3306,15 @@ dependencies = [
 name = "roc_ident"
 version = "0.1.0"
 
+[[package]]
+name = "roc_linker"
+version = "0.1.0"
+dependencies = [
+ "bumpalo",
+ "clap 3.0.0-beta.1",
+ "object 0.26.0",
+]
+
 [[package]]
 name = "roc_load"
 version = "0.1.0"

Cargo.toml

@@ -32,6 +32,7 @@ members = [
     "cli/cli_utils",
     "roc_std",
     "docs",
+    "linker",
 ]
 exclude = [ "ci/bench-runner" ]
 # Needed to be able to run `cargo run -p roc_cli --no-default-features` -

linker/Cargo.toml

@@ -0,0 +1,24 @@
+[package]
+name = "roc_linker"
+version = "0.1.0"
+authors = ["The Roc Contributors"]
+license = "UPL-1.0"
+repository = "https://github.com/rtfeldman/roc"
+edition = "2018"
+description = "A surgical linker for Roc"
+
+[lib]
+name = "roc_linker"
+path = "src/lib.rs"
+
+[[bin]]
+name = "link"
+path = "src/main.rs"
+test = false
+bench = false
+
+[dependencies]
+# TODO switch to clap 3.0.0 once it's out. Tried adding clap = "~3.0.0-beta.1" and cargo wouldn't accept it
+clap = { git = "https://github.com/rtfeldman/clap", branch = "master" }
+object = { version = "0.26", features = ["read"] }
+bumpalo = { version = "3.6.1", features = ["collections"] }

linker/README.md

@@ -0,0 +1,31 @@
+# The Roc Surgical Linker
+
+This linker has the goal of being extremely slim lined and fast.
+It is focused on the scope of only linking platforms to Roc applications.
+This restriction enables ignoring most of linking.
+
+## General Overview
+
+This linker is run in 2 phases: preprocessing and surigical linking.
+
+### Platform Preprocessor
+
+1. Dynamically link the platform to a dummy Roc application dynamic library
+1. Create metadata related to Roc dynamically linked functions
+   - Symbols that need to be redefined
+   - Call locations that need to be modified for each symbol
+   - Locations of special roc functions (roc_alloc, roc_dealloc, builtins, etc)
+1. Modify the main executable to no longer be dynamically link
+   - Delete dependency on dynamic library
+   - Remove symbols from the dynamic table (maybe add them to the regular table?)
+   - Delete GOT and PLT entries
+   - Remove relocations from the dynamic table
+   - Add extra header information about new text and data section at end of file
+
+### Surgical Linker
+
+1. Copy over preprocessed platform as base
+1. Append text and data of application, noting offset
+   - This could potentially have extra complication around section locations and updating the header
+1. Surgically update all call locations in the platform
+1. Surgically update call information in the application (also dealing with other relocations for builtins)

linker/src/lib.rs

@@ -0,0 +1,34 @@
+use clap::{App, AppSettings, Arg};
+use std::io;
+
+pub const CMD_PREPROCESS: &str = "preprocess";
+pub const CMD_SURGERY: &str = "surgery";
+pub const EXEC: &str = "EXEC";
+pub const SHARED_LIB: &str = "SHARED_LIB";
+
+pub fn build_app<'a>() -> App<'a> {
+    App::new("link")
+        .about("Preprocesses a platform and surgically links it to an application.")
+        .setting(AppSettings::SubcommandRequiredElseHelp)
+        .subcommand(
+            App::new(CMD_PREPROCESS)
+                .about("Preprocesses a dynamically linked platform to prepare for linking.")
+                .arg(
+                    Arg::with_name(EXEC)
+                        .help("The dynamically link platform executable")
+                        .required(true),
+                )
+                .arg(
+                    Arg::with_name(SHARED_LIB)
+                        .help("The dummy shared library representing the Roc application")
+                        .required(true),
+                ),
+        )
+        .subcommand(
+            App::new(CMD_SURGERY).about("Links a preprocessed platform with a Roc application."),
+        )
+}
+
+pub fn preprocess() -> io::Result<()> {
+    panic!("sad");
+}

linker/src/main.rs

@@ -0,0 +1,17 @@
+use roc_linker::{build_app, preprocess, CMD_PREPROCESS, CMD_SURGERY};
+use std::io;
+
+fn main() -> io::Result<()> {
+    let matches = build_app().get_matches();
+
+    let exit_code = match matches.subcommand_name() {
+        None => Ok::<i32, io::Error>(-1),
+        Some(CMD_PREPROCESS) => {
+            preprocess()?;
+            Ok(0)
+        }
+        Some(CMD_SURGERY) => Ok(0),
+        _ => unreachable!(),
+    }?;
+    std::process::exit(exit_code);
+}

linker/tests/.gitignore

@@ -0,0 +1 @@
+*.so

linker/tests/Makefile

@@ -0,0 +1,12 @@
+SHLIB_LDFLAGS = -shared -Wl,--allow-shlib-undefined
+
+all: platform
+
+platform: platform.c libapp.so
+	$(CC) -O2 -fPIC -o $@ $^
+
+libapp.so: app.c
+	$(CC) -O2 -fPIC -shared -o $@ $^
+
+clean:
+	rm -f platform libapp.so

linker/tests/app.c

@@ -0,0 +1,3 @@
+#include <stdio.h>
+
+void app() { printf("Hello World from the application"); }

linker/tests/platform.c

@@ -0,0 +1,9 @@
+#include <stdio.h>
+
+void app();
+
+int main() {
+  printf("Hello World from the platform");
+  app();
+  return 0;
+}