getenv works

example-user/src/main.rs

@@ -4,7 +4,7 @@
 
 use core::ffi::c_char;
 
-use libuwuc::println;
+use libuwuc::{println, utils::SharedThinCstr};
 
 extern crate libuwuc;
 
@@ -23,5 +23,15 @@ fn handler(arg: &core::panic::PanicInfo) -> ! {
 #[no_mangle]
 extern "C" fn main(_argc: i32, _argv: *const *const c_char) -> i32 {
     println!("Hello, world!");
+    let pwd = libuwuc::env::getenv(SharedThinCstr::from_array(b"PWD\0"));
+    println!("PWD={pwd:?}");
     0
 }
+
+// libcore seems to require this symbol, even though it's unused.
+#[no_mangle]
+fn rust_eh_personality() {
+    unsafe {
+        libuwuc::trap!();
+    }
+}

src/env.rs

@@ -1,35 +1,38 @@
-use core::ffi::CStr;
+use core::{
+    ffi::{c_char, CStr},
+    iter,
+    ptr::NonNull,
+};
 
 use crate::{println, utils::SharedThinCstr};
 
 mod global {
-    use core::cell::UnsafeCell;
+    use core::{cell::UnsafeCell, ptr::NonNull};
 
     use crate::utils::{SharedThinCstr, SyncUnsafeCell};
 
     use super::EnvP;
 
-    static ENVP: SyncUnsafeCell<EnvP> =
-        SyncUnsafeCell(UnsafeCell::new(EnvP(core::ptr::null_mut())));
+    static ENVP: SyncUnsafeCell<EnvP> = SyncUnsafeCell(UnsafeCell::new(EnvP(None)));
 
-    pub(super) unsafe fn init(envp: *mut SharedThinCstr) {
-        assert!((*ENVP.0.get()).0.is_null());
-        *ENVP.0.get() = EnvP(envp);
+    pub(super) unsafe fn init(envp: *mut Option<SharedThinCstr>) {
+        assert!((*ENVP.0.get()).0.is_none());
+        *ENVP.0.get() = EnvP(Some(NonNull::new(envp).unwrap()));
     }
 
     pub(super) fn get() -> EnvP {
         let ptr = unsafe { *ENVP.0.get() };
-        assert!(!ptr.0.is_null());
+        assert!(ptr.0.is_some());
         ptr
     }
 }
 
-pub(crate) unsafe fn init(envp: *mut SharedThinCstr) {
+pub(crate) unsafe fn init(envp: *mut Option<SharedThinCstr>) {
     global::init(envp);
 }
 
 #[derive(Clone, Copy)]
-struct EnvP(*mut SharedThinCstr);
+struct EnvP(Option<NonNull<Option<SharedThinCstr>>>);
 
 unsafe impl Sync for EnvP {}
 
@@ -38,13 +41,12 @@ impl Iterator for EnvP {
 
     fn next(&mut self) -> Option<Self::Item> {
         unsafe {
-            let value: SharedThinCstr = self.0.read();
-            if value.0.is_null() {
-                None
-            } else {
-                self.0 = self.0.add(1);
-                Some(value)
-            }
+            let value: Option<SharedThinCstr> = self.0.unwrap().as_ptr().read();
+
+            value.map(|value| {
+                self.0 = Some(NonNull::new_unchecked(self.0.unwrap().as_ptr().add(1)));
+                value
+            })
         }
     }
 }
@@ -57,3 +59,99 @@ pub(crate) fn debug_env() {
     });
     println!("end vars");
 }
+
+pub fn getenv(name: SharedThinCstr) -> Option<SharedThinCstr> {
+    getenv_inner(global::get(), name)
+}
+
+fn getenv_inner(mut envp: EnvP, name: SharedThinCstr) -> Option<SharedThinCstr> {
+    let mut eq_idx = 0;
+    envp.find(|env| {
+        // Find ENV
+        // EN=x
+        // ENV=x   <- this one
+        // ENVNO=x
+
+        let mut name_iter = name.into_iter();
+        let mut env_iter = env.into_iter();
+        eq_idx = 0;
+        loop {
+            let name = name_iter.next().map(|c| c as u8);
+            let env = env_iter.next().map(|c| c as u8);
+            if let (None, Some(b'=')) = (name, env) {
+                return true;
+            }
+            if name.is_none() || env == Some(b'=') {
+                return false;
+            }
+            eq_idx += 1;
+        }
+    })
+    .map(|elem| {
+        let value_idx = eq_idx + 1;
+        unsafe { elem.add(value_idx) }
+    })
+}
+
+#[cfg(test)]
+mod tests {
+    use core::ptr::NonNull;
+    use std::string::ToString;
+    use std::{ffi::CString, vec::Vec};
+
+    use crate::utils::SharedThinCstr;
+
+    use super::EnvP;
+
+    fn cstr(s: &str) -> SharedThinCstr {
+        assert_eq!(s.as_bytes()[s.len() - 1], 0);
+        unsafe { SharedThinCstr::from_ptr(NonNull::new(s.as_ptr() as _).unwrap()) }
+    }
+
+    fn with_envp(env: &[&str], f: impl FnOnce(EnvP)) {
+        let cstrs = env
+            .iter()
+            .map(|s| CString::new(s.to_string()).unwrap())
+            .collect::<Vec<_>>();
+
+        let mut envs: Vec<Option<SharedThinCstr>> = cstrs
+            .iter()
+            .map(|cstr| unsafe {
+                Some(SharedThinCstr::from_ptr(
+                    NonNull::new(cstr.as_ptr() as _).unwrap(),
+                ))
+            })
+            .collect();
+        envs.push(None);
+
+        let envp = EnvP(Some(NonNull::new(envs.as_ptr() as _).unwrap()));
+        f(envp)
+    }
+
+    #[test]
+    fn getenv_exact_first() {
+        with_envp(&["UWU=a"], |envp| {
+            assert_eq!(
+                super::getenv_inner(envp, cstr("UWU\0")).unwrap(),
+                cstr("a\0")
+            );
+        })
+    }
+
+    #[test]
+    fn getenv_previous_mismatches() {
+        with_envp(&["UW=a", "UWUU=b", "UWU=c"], |envp| {
+            assert_eq!(
+                super::getenv_inner(envp, cstr("UWU\0")).unwrap(),
+                cstr("c\0")
+            );
+        })
+    }
+
+    #[test]
+    fn getenv_name_long() {
+        with_envp(&["U=w"], |envp| {
+            assert_eq!(super::getenv_inner(envp, cstr("LONG_NAME\0")), None);
+        })
+    }
+}

src/lib.rs

@@ -1,13 +1,16 @@
 #![no_std]
 #![warn(unreachable_pub)]
 
+#[cfg(test)]
+extern crate std;
+
 mod basic_mem;
-mod env;
+pub mod env;
 pub mod io;
 pub mod start;
 mod stubs;
 mod sys;
-mod utils;
+pub mod utils;
 
 pub mod syscall {
     pub use crate::sys::syscall::*;

src/start.rs

@@ -5,7 +5,7 @@ use crate::utils::SharedThinCstr;
 /// The entrypoint of the program.
 /// This is called by a bit of assembly handling architecture-specific _start.
 pub(crate) unsafe extern "C" fn start(argc: u64, argv: *const *const c_char, rsp: u64) -> ! {
-    let envp = (8 + 8 * argc + rsp + 8) as *mut SharedThinCstr;
+    let envp = (8 + 8 * argc + rsp + 8) as *mut Option<SharedThinCstr>;
 
     crate::env::init(envp);
 
@@ -13,7 +13,7 @@ pub(crate) unsafe extern "C" fn start(argc: u64, argv: *const *const c_char, rsp
         fn main(argc: c_int, argv: *const *const c_char) -> c_int;
     }
 
-    crate::env::debug_env();
+    // crate::env::debug_env();
 
     let result = main(argc as i32, argv);
 

src/stubs.rs

@@ -1,7 +0,0 @@
-// libcore seems to require this symbol, even though it's unused.
-#[no_mangle]
-fn rust_eh_personality() {
-    unsafe {
-        crate::sys::helpers::trap!();
-    }
-}

src/sys/x86_64/helpers.rs

@@ -1,3 +1,4 @@
+#[macro_export]
 macro_rules! trap {
     () => {
         ::core::arch::asm!("ud2");

src/utils/mod.rs

@@ -1,6 +1,8 @@
 use core::{
     cell::UnsafeCell,
     ffi::{c_char, CStr},
+    fmt::Debug,
+    ptr::NonNull,
 };
 
 #[repr(transparent)]
@@ -9,18 +11,84 @@ pub(crate) struct SyncUnsafeCell<T>(pub(crate) UnsafeCell<T>);
 
 unsafe impl<T: Sync> Sync for SyncUnsafeCell<T> {}
 
+#[derive(Clone, Copy)]
 #[repr(transparent)]
-pub(crate) struct SharedThinCstr(pub(crate) *const c_char);
+pub struct SharedThinCstr(pub NonNull<c_char>);
+
+impl SharedThinCstr {
+    pub unsafe fn from_ptr(ptr: NonNull<c_char>) -> Self {
+        Self(ptr)
+    }
+
+    pub fn from_array<const N: usize>(arr: &[u8; N]) -> Self {
+        assert!(arr[N - 1] == 0);
+        unsafe { Self(NonNull::new_unchecked(arr as *const u8 as *mut c_char)) }
+    }
+
+    pub fn as_ptr(self) -> NonNull<c_char> {
+        self.0
+    }
+
+    pub unsafe fn add(self, amount: usize) -> Self {
+        Self(NonNull::new_unchecked(self.0.as_ptr().add(amount)))
+    }
+}
+
+impl IntoIterator for SharedThinCstr {
+    type Item = c_char;
+
+    type IntoIter = CStrIter;
+
+    fn into_iter(self) -> Self::IntoIter {
+        CStrIter(self)
+    }
+}
+
+pub struct CStrIter(SharedThinCstr);
+
+impl Iterator for CStrIter {
+    type Item = c_char;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        unsafe {
+            let c = self.0 .0.as_ptr().read();
+            if c == 0 {
+                return None;
+            }
+
+            self.0 = self.0.add(1);
+            Some(c)
+        }
+    }
+}
 
 unsafe impl Send for SharedThinCstr {}
 unsafe impl Sync for SharedThinCstr {}
 
-impl From<SharedThinCstr> for &CStr {
-    fn from(value: SharedThinCstr) -> Self {
-        unsafe { CStr::from_ptr(value.0) }
+impl Debug for SharedThinCstr {
+    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
+        let str = <&CStr>::from(*self).to_str();
+        match str {
+            Ok(str) => f.write_str(str),
+            Err(_) => f.write_str("<invalid UTF-8>"),
+        }
     }
 }
 
+impl From<SharedThinCstr> for &CStr {
+    fn from(value: SharedThinCstr) -> Self {
+        unsafe { CStr::from_ptr(value.0.as_ptr()) }
+    }
+}
+
+impl PartialEq for SharedThinCstr {
+    fn eq(&self, other: &Self) -> bool {
+        self.into_iter().eq(other.into_iter())
+    }
+}
+
+impl Eq for SharedThinCstr {}
+
 #[repr(transparent)]
 pub(crate) struct SyncPtr<T>(pub(crate) *mut T);