libc + tlibc works for memory mapping functions.

applications/test_libc/Cargo.toml

@@ -0,0 +1,14 @@
+[package]
+authors = ["Kevin Boos <kevinaboos@gmail.com>"]
+name = "test_libc"
+description = "A crate for testing tlibc with the libc Rust crate ported to Theseus"
+version = "0.1.0"
+build = "../../build.rs"
+
+[dependencies]
+log = "0.4.8"
+libc = { version = "0.2", default-features = false }
+
+
+[lib]
+crate-type = ["rlib"]

applications/test_libc/src/lib.rs

@@ -0,0 +1,39 @@
+//! A simple test crate for trying to build and use libc from Rust in Theseus.
+//! 
+//! This involves a ported version of the Rust libc crate that must be built in a way
+//! that uses Theseus's `tlibc` as the underlying libc implementation. 
+
+#![no_std]
+
+use core::ptr;
+
+use alloc::{vec::Vec, string::String};
+
+extern crate alloc;
+#[macro_use] extern crate log;
+extern crate libc;
+
+
+pub fn main(_args: Vec<String>) -> isize {
+    test_mmap();
+    test_printf();
+    0
+}
+
+fn test_mmap() {
+    warn!("Hello from test_mmap()");
+    let ret = unsafe {
+        libc::mmap(ptr::null_mut(), 100, 0, 0, 0, 0)
+    };
+    warn!("test_mmap: mmap returned {:?}", ret);
+}
+
+
+fn test_printf() {
+    warn!("Hello from test_printf()");
+    let ret = unsafe {
+        libc::printf(b"%d".as_ptr() as *const i8, 17);
+    };
+    warn!("test_printf: printf returned {:?}", ret);
+}
+

cfg/x86_64-theseus.json

@@ -1,8 +1,10 @@
 {
-  "llvm-target": "x86_64-unknown-none-gnu",
+  "__use_custom_libc_sysroot": "https://stackoverflow.com/questions/41901024/how-can-i-make-my-rust-program-link-to-another-glibc",
+  "llvm-target": "x86_64-unknown-none-elf",
   "__data-layout": "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128",
   "data-layout": "e-m:e-i64:64-f80:128-n8:16:32:64-S128",
   "linker-flavor": "gcc",
+  "env": "tlibc",
   "target-endian": "little",
   "target-pointer-width": "64",
   "target-c-int-width": "32",

tlibc/.gitignore

@@ -0,0 +1 @@
+target/