Add build script to extract a list of registered syscalls

The list is used in cargo-build-bpf to check generated .so modules for
undefined symbols that are not known run-time syscalls.

programs/bpf_loader/Cargo.toml

@@ -9,6 +9,9 @@ homepage = "https://solana.com/"
 documentation = "https://docs.rs/solana-bpf-loader-program"
 edition = "2018"
 
+[build-dependencies]
+regex = "1.5.4"
+
 [dependencies]
 bincode = "1.3.1"
 byteorder = "1.3.4"

programs/bpf_loader/build.rs

@@ -0,0 +1,34 @@
+use regex::Regex;
+use std::{
+    fs::File,
+    io::{prelude::*, BufWriter, Read},
+    path::PathBuf,
+    process::exit,
+    str,
+};
+
+/**
+ * Extract a list of registered syscall names and save it in a file
+ * for distribution with the SDK.  This file is read by cargo-build-bpf
+ * to verify undefined symbols in a .so module that cargo-build-bpf has built.
+ */
+fn main() {
+    let path = PathBuf::from("src/syscalls.rs");
+    let mut file = match File::open(&path) {
+        Ok(x) => x,
+        _ => exit(1),
+    };
+    let mut text = vec![];
+    file.read_to_end(&mut text).unwrap();
+    let text = str::from_utf8(&text).unwrap();
+    let path = PathBuf::from("../../sdk/bpf/syscalls.txt");
+    let file = match File::create(&path) {
+        Ok(x) => x,
+        _ => exit(1),
+    };
+    let mut out = BufWriter::new(file);
+    let sysc_re = Regex::new(r#"register_syscall_by_name\([[:space:]]*b"([^"]+)","#).unwrap();
+    for caps in sysc_re.captures_iter(&text) {
+        writeln!(out, "{}", caps[1].to_string()).unwrap();
+    }
+}