Add helper crate to generate syscalls.txt

programs/bpf_loader/gen-syscall-list/Cargo.toml

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+[package]
+name = "gen-syscall-list"
+version = "1.10.0"
+edition = "2021"
+license = "Apache-2.0"
+publish = false
+
+[build-dependencies]
+regex = "1.5.4"

programs/bpf_loader/gen-syscall-list/build.rs

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+use {
+    regex::Regex,
+    std::{
+        fs::File,
+        io::{prelude::*, BufWriter, Read},
+        path::PathBuf,
+        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 syscalls_rs_path = PathBuf::from("../src/syscalls.rs");
+    let syscalls_txt_path = PathBuf::from("../../../sdk/bpf/syscalls.txt");
+    println!(
+        "cargo:warning=(not a warning) Generating {1} from {0}",
+        syscalls_rs_path.display(),
+        syscalls_txt_path.display()
+    );
+
+    let mut file = match File::open(&syscalls_rs_path) {
+        Ok(x) => x,
+        Err(err) => panic!("Failed to open {}: {}", syscalls_rs_path.display(), err),
+    };
+    let mut text = vec![];
+    file.read_to_end(&mut text).unwrap();
+    let text = str::from_utf8(&text).unwrap();
+    let file = match File::create(&syscalls_txt_path) {
+        Ok(x) => x,
+        Err(err) => panic!("Failed to create {}: {}", syscalls_txt_path.display(), err),
+    };
+    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) {
+        let name = caps[1].to_string();
+        writeln!(out, "{}", name).unwrap();
+    }
+}

programs/bpf_loader/gen-syscall-list/src/main.rs

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+fn main() {
+    /* I do all my work in `../build.rs` */
+}