firmware: rewrite the dynamic linker in Rust.

artiq/firmware/Cargo.lock

@@ -62,6 +62,10 @@ dependencies = [
  "std_artiq 0.0.0",
 ]
 
+[[package]]
+name = "dyld"
+version = "0.0.0"
+
 [[package]]
 name = "fringe"
 version = "1.1.0"
@@ -93,6 +97,7 @@ dependencies = [
  "build_artiq 0.0.0",
  "byteorder 1.0.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "cslice 0.3.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "dyld 0.0.0",
  "std_artiq 0.0.0",
 ]
 
@@ -136,6 +141,7 @@ dependencies = [
  "compiler_builtins 0.1.0 (git+https://github.com/rust-lang-nursery/compiler-builtins?rev=631b568)",
  "cslice 0.3.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "drtioaux 0.0.0",
+ "dyld 0.0.0",
  "fringe 1.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "log 0.3.6 (registry+https://github.com/rust-lang/crates.io-index)",
  "logger_artiq 0.0.0",

artiq/firmware/ksupport/Cargo.toml

@@ -16,5 +16,6 @@ build_artiq = { path = "../libbuild_artiq" }
 alloc_none = { path = "../liballoc_none" }
 std_artiq = { path = "../libstd_artiq" }
 board = { path = "../libboard" }
+dyld = { path = "../libdyld" }
 byteorder = { version = "1.0", default-features = false }
 cslice = { version = "0.3" }

artiq/firmware/ksupport/Makefile

@@ -11,8 +11,7 @@ LDFLAGS += --eh-frame-hdr \
 	-L../libcompiler-rt \
 	-L../libbase \
 	-L../libm \
-	-L../libunwind \
+	-L../libunwind
-	-L../libdyld
 
 RUSTFLAGS += -Cpanic=unwind
 
@@ -24,7 +23,7 @@ $(RUSTOUT)/libksupport.a:
 
 ksupport.elf: $(RUSTOUT)/libksupport.a glue.o
 	$(LD) $(LDFLAGS) -T $(KSUPPORT_DIRECTORY)/ksupport.ld -o $@ $^ \
-		-lbase -lm -lcompiler-rt -ldyld -lunwind
+		-lbase -lm -lcompiler-rt -lunwind
 	@chmod -x $@
 
 %.o: $(KSUPPORT_DIRECTORY)/%.c

artiq/firmware/ksupport/api.rs

@@ -12,12 +12,11 @@ macro_rules! api {
     }
 }
 
-pub fn resolve(required: &str) -> usize {
+pub fn resolve(required: &[u8]) -> Option<u32> {
     unsafe {
         API.iter()
-           .find(|&&(exported, _)| exported == required)
+           .find(|&&(exported, _)| exported.as_bytes() == required)
-           .map(|&(_, ptr)| ptr as usize)
+           .map(|&(_, ptr)| ptr as u32)
-           .unwrap_or(0)
     }
 }
 

artiq/firmware/ksupport/dyld.rs

@@ -1,56 +0,0 @@
-use core::{ptr, slice, str};
-use libc::{c_void, c_char, c_int, size_t};
-
-#[allow(non_camel_case_types)]
-#[repr(C)]
-#[derive(Default)]
-struct dyld_info {
-    __opaque: [usize; 7]
-}
-
-extern {
-    fn dyld_load(shlib: *const c_void, base: usize,
-                 resolve: extern fn(*mut c_void, *const c_char) -> usize,
-                 resolve_data: *mut c_void,
-                 info: *mut dyld_info, error_out: *mut *const c_char) -> c_int;
-    fn dyld_lookup(symbol: *const c_char, info: *const dyld_info) -> *const c_void;
-
-    fn strlen(ptr: *const c_char) -> size_t;
-}
-
-pub struct Library {
-    lower: dyld_info
-}
-
-impl Library {
-    pub unsafe fn load<F>(shlib: &[u8], base: usize, mut resolve: F)
-                -> Result<Library, &'static str>
-            where F: Fn(&str) -> usize {
-        extern fn wrapper<F>(data: *mut c_void, name: *const c_char) -> usize
-                where F: Fn(&str) -> usize {
-            unsafe {
-                let f = data as *mut F;
-                let name = slice::from_raw_parts(name as *const u8, strlen(name));
-                (*f)(str::from_utf8_unchecked(name))
-            }
-        }
-
-        let mut library = Library { lower: dyld_info::default() };
-        let mut error: *const c_char = ptr::null();
-        if dyld_load(shlib.as_ptr() as *const _, base,
-                     wrapper::<F>, &mut resolve as *mut _ as *mut _,
-                     &mut library.lower, &mut error) == 0 {
-            let error = slice::from_raw_parts(error as *const u8, strlen(error));
-            Err(str::from_utf8_unchecked(error))
-        } else {
-            Ok(library)
-        }
-    }
-
-    pub unsafe fn lookup(&self, symbol: &str) -> usize {
-        assert!(symbol.len() < 32);
-        let mut buf = [0u8; 32];
-        buf[0..symbol.as_bytes().len()].copy_from_slice(symbol.as_bytes());
-        dyld_lookup(&buf as *const _ as *const c_char, &self.lower) as usize
-    }
-}

artiq/firmware/ksupport/lib.rs

@@ -9,6 +9,7 @@ extern crate libc;
 extern crate byteorder;
 extern crate board;
 extern crate cslice;
+extern crate dyld;
 
 #[path = "../runtime/mailbox.rs"]
 mod mailbox;
@@ -20,10 +21,9 @@ mod kernel_proto;
 #[path = "../runtime/rpc_proto.rs"]
 mod rpc_proto;
 
-mod dyld;
 mod api;
 
-use core::{mem, ptr, str};
+use core::{mem, ptr, slice, str};
 use std::io::Cursor;
 use cslice::{CSlice, AsCSlice};
 use kernel_proto::*;
@@ -294,8 +294,12 @@ unsafe fn attribute_writeback(typeinfo: *const ()) {
 
 #[no_mangle]
 pub unsafe fn main() {
+    let image = slice::from_raw_parts_mut(kernel_proto::KERNELCPU_PAYLOAD_ADDRESS as *mut u8,
+                                          kernel_proto::KERNELCPU_LAST_ADDRESS -
+                                          kernel_proto::KERNELCPU_PAYLOAD_ADDRESS);
+
     let library = recv!(&LoadRequest(library) => {
-        match Library::load(library, kernel_proto::KERNELCPU_PAYLOAD_ADDRESS, api::resolve) {
+        match Library::load(library, image, &api::resolve) {
             Err(error) => {
                 send(&LoadReply(Err(error)));
                 loop {}
@@ -307,16 +311,16 @@ pub unsafe fn main() {
         }
     });
 
-    let __bss_start = library.lookup("__bss_start");
+    let __bss_start = library.lookup(b"__bss_start").unwrap();
-    let _end = library.lookup("_end");
+    let _end = library.lookup(b"_end").unwrap();
-    ptr::write_bytes(__bss_start as *mut u8, 0, _end - __bss_start);
+    ptr::write_bytes(__bss_start as *mut u8, 0, (_end - __bss_start) as usize);
 
     send(&NowInitRequest);
     recv!(&NowInitReply(now) => NOW = now);
-    (mem::transmute::<usize, fn()>(library.lookup("__modinit__")))();
+    (mem::transmute::<u32, fn()>(library.lookup(b"__modinit__").unwrap()))();
     send(&NowSave(NOW));
 
-    attribute_writeback(library.lookup("typeinfo") as *const ());
+    attribute_writeback(library.lookup(b"typeinfo").unwrap_or(0) as *const ());
 
     send(&RunFinished);
 

artiq/firmware/libdyld/Cargo.toml

@@ -0,0 +1,8 @@
+[package]
+authors = ["M-Labs"]
+name = "dyld"
+version = "0.0.0"
+
+[lib]
+name = "dyld"
+path = "lib.rs"

artiq/firmware/libdyld/lib.rs

@@ -0,0 +1,313 @@
+#![no_std]
+#![feature(untagged_unions, ptr_unaligned)]
+
+use core::{mem, ptr, fmt, slice, str, convert};
+use elf::*;
+
+pub mod elf;
+
+fn read_unaligned<T: Copy>(data: &[u8], offset: usize) -> Result<T, ()> {
+    if data.len() < offset + mem::size_of::<T>() {
+        Err(())
+    } else {
+        let ptr = data.as_ptr().wrapping_offset(offset as isize) as *const T;
+        Ok(unsafe { ptr::read_unaligned(ptr) })
+    }
+}
+
+fn get_ref<T: Copy>(data: &[u8], offset: usize) -> Result<&T, ()> {
+    if data.len() < offset + mem::size_of::<T>() {
+        Err(())
+    } else if (data.as_ptr() as usize + offset) & (mem::align_of::<T>() - 1) != 0 {
+        Err(())
+    } else {
+        let ptr = data.as_ptr().wrapping_offset(offset as isize) as *const T;
+        Ok(unsafe { &*ptr })
+    }
+}
+
+fn get_ref_slice<T: Copy>(data: &[u8], offset: usize, len: usize) -> Result<&[T], ()> {
+    if data.len() < offset + mem::size_of::<T>() * len {
+        Err(())
+    } else if (data.as_ptr() as usize + offset) & (mem::align_of::<T>() - 1) != 0 {
+        Err(())
+    } else {
+        let ptr = data.as_ptr().wrapping_offset(offset as isize) as *const T;
+        Ok(unsafe { slice::from_raw_parts(ptr, len) })
+    }
+}
+
+fn elf_hash(name: &[u8]) -> u32 {
+    let mut h: u32 = 0;
+    for c in name {
+        h = (h << 4) + *c as u32;
+        let g = h & 0xf0000000;
+        if g != 0 {
+            h ^= g >> 24;
+            h &= !g;
+        }
+    }
+    h
+}
+
+#[derive(Debug)]
+pub enum Error<'a> {
+    Parsing(&'static str),
+    Lookup(&'a [u8])
+}
+
+impl<'a> convert::From<&'static str> for Error<'a> {
+    fn from(desc: &'static str) -> Error<'a> {
+        Error::Parsing(desc)
+    }
+}
+
+impl<'a> fmt::Display for Error<'a> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        match self {
+            &Error::Parsing(desc) =>
+                write!(f, "parse error: {}", desc),
+            &Error::Lookup(sym) =>
+                match str::from_utf8(sym) {
+                    Ok(sym) => write!(f, "symbol lookup error: {}", sym),
+                    Err(_)  => write!(f, "symbol lookup error: {:?}", sym)
+                }
+        }
+    }
+}
+
+pub struct Library<'a> {
+    image_off:   Elf32_Addr,
+    image_sz:    usize,
+    strtab:      &'a [u8],
+    symtab:      &'a [Elf32_Sym],
+    hash_bucket: &'a [Elf32_Word],
+    hash_chain:  &'a [Elf32_Word],
+}
+
+impl<'a> Library<'a> {
+    pub fn lookup(&self, name: &[u8]) -> Option<Elf32_Word> {
+        let hash = elf_hash(name);
+        let mut index = self.hash_bucket[hash as usize % self.hash_bucket.len()] as usize;
+
+        loop {
+            if index == STN_UNDEF { return None }
+
+            let sym = &self.symtab[index];
+            let sym_name_off = sym.st_name as usize;
+            match self.strtab.get(sym_name_off..sym_name_off + name.len()) {
+                Some(sym_name) if sym_name == name => {
+                    if ELF32_ST_BIND(sym.st_info) & STB_GLOBAL == 0 {
+                        return None
+                    }
+
+                    match sym.st_shndx {
+                        SHN_UNDEF => return None,
+                        SHN_ABS => return Some(sym.st_value),
+                        _ => return Some(self.image_off + sym.st_value)
+                    }
+                }
+                _ => (),
+            }
+
+            index = self.hash_chain[index] as usize;
+        }
+    }
+
+    fn fixup_rela(&self, rela: &Elf32_Rela, resolve: &Fn(&[u8]) -> Option<Elf32_Word>)
+            -> Result<(), Error<'a>> {
+        let sym;
+        if ELF32_R_SYM(rela.r_info) == 0 {
+            sym = None;
+        } else {
+            sym = Some(self.symtab.get(ELF32_R_SYM(rela.r_info) as usize)
+                                  .ok_or("symbol out of bounds of symbol table")?)
+        }
+
+        let value;
+        match ELF32_R_TYPE(rela.r_info) {
+            R_OR1K_NONE =>
+                return Ok(()),
+
+            R_OR1K_RELATIVE =>
+                value = self.image_off + rela.r_addend as Elf32_Word,
+
+            R_OR1K_32 | R_OR1K_GLOB_DAT | R_OR1K_JMP_SLOT => {
+                let sym = sym.ok_or("relocation requires an associated symbol")?;
+
+                let sym_name_off = sym.st_name as usize;
+                let sym_name_end =
+                    self.strtab.iter().skip(sym_name_off).position(|&x| x == 0)
+                               .ok_or("symbol in symbol table not null-terminated")?;
+                let sym_name =
+                    self.strtab.get(sym_name_off..sym_name_off + sym_name_end)
+                               .ok_or("cannot read symbol name")?;
+
+                // First, try to resolve against itself.
+                match self.lookup(sym_name) {
+                    Some(addr) => value = addr,
+                    None => {
+                        // Second, call the user-provided function.
+                        match resolve(sym_name) {
+                            Some(addr) => value = addr,
+                            None => {
+                                // We couldn't find it anywhere.
+                                return Err(Error::Lookup(sym_name))
+                            }
+                        }
+                    }
+                }
+            }
+
+            _ => return Err("unsupported relocation type")?
+        }
+
+        if rela.r_offset as usize + mem::size_of::<Elf32_Addr>() > self.image_sz {
+            return Err("relocation out of image bounds")?
+        }
+
+        let ptr = (self.image_off + rela.r_offset) as *mut Elf32_Addr;
+        unsafe { *ptr = value }
+
+        Ok(())
+    }
+
+    pub fn load(data: &[u8], image: &'a mut [u8], resolve: &Fn(&[u8]) -> Option<Elf32_Word>)
+            -> Result<Library<'a>, Error<'a>> {
+        let ehdr = read_unaligned::<Elf32_Ehdr>(data, 0)
+                                  .map_err(|()| "cannot read ELF header")?;
+
+        const IDENT: [u8; EI_NIDENT] = [
+            ELFMAG0,    ELFMAG1,     ELFMAG2,    ELFMAG3,
+            ELFCLASS32, ELFDATA2MSB, EV_CURRENT, ELFOSABI_NONE,
+            /* ABI version */ 0, /* padding */ 0, 0, 0, 0, 0, 0, 0
+        ];
+
+        #[cfg(target_arch = "or1k")]
+        const ARCH: u16 = EM_OPENRISC;
+        #[cfg(not(target_arch = "or1k"))]
+        const ARCH: u16 = EM_NONE;
+
+        if ehdr.e_ident != IDENT || ehdr.e_type != ET_DYN || ehdr.e_machine != ARCH {
+            return Err("not a shared library for current architecture")?
+        }
+
+        let mut dyn_off = None;
+        for i in 0..ehdr.e_phnum {
+            let phdr_off = ehdr.e_phoff as usize + mem::size_of::<Elf32_Phdr>() * i as usize;
+            let phdr = read_unaligned::<Elf32_Phdr>(data, phdr_off)
+                                      .map_err(|()| "cannot read program header")?;
+
+            match phdr.p_type {
+                PT_LOAD => {
+                    if (phdr.p_vaddr + phdr.p_filesz) as usize > image.len() ||
+                            (phdr.p_offset + phdr.p_filesz) as usize > data.len() {
+                        return Err("program header requests an out of bounds load")?
+                    }
+                    let dst = image.get_mut(phdr.p_vaddr as usize..
+                                            (phdr.p_vaddr + phdr.p_filesz) as usize)
+                                   .ok_or("cannot write to program header destination")?;
+                    let src = data.get(phdr.p_offset as usize..
+                                       (phdr.p_offset + phdr.p_filesz) as usize)
+                                  .ok_or("cannot read from program header source")?;
+                    dst.copy_from_slice(src);
+                }
+
+                PT_DYNAMIC =>
+                    dyn_off = Some(phdr.p_vaddr),
+
+                _ => ()
+            }
+        }
+
+        let (mut strtab_off, mut strtab_sz) = (0, 0);
+        let (mut symtab_off, mut symtab_sz) = (0, 0);
+        let (mut rela_off,   mut rela_sz)   = (0, 0);
+        let (mut pltrel_off, mut pltrel_sz) = (0, 0);
+        let (mut hash_off,   mut hash_sz)   = (0, 0);
+        let mut sym_ent  = 0;
+        let mut rela_ent = 0;
+        let mut nbucket  = 0;
+        let mut nchain   = 0;
+
+        let dyn_off = dyn_off.ok_or("cannot find a dynamic header")?;
+        for i in 0.. {
+            let dyn_off = dyn_off as usize + i * mem::size_of::<Elf32_Dyn>();
+            let dyn = get_ref::<Elf32_Dyn>(image, dyn_off)
+                              .map_err(|()| "cannot read dynamic header")?;
+
+            let val = unsafe { dyn.d_un.d_val } as usize;
+            match dyn.d_tag {
+                DT_NULL     => break,
+                DT_REL      => return Err("relocations with implicit addend are not supported")?,
+                DT_STRTAB   => strtab_off = val,
+                DT_STRSZ    => strtab_sz  = val,
+                DT_SYMTAB   => symtab_off = val,
+                DT_SYMENT   => sym_ent    = val,
+                DT_RELA     => rela_off   = val,
+                DT_RELASZ   => rela_sz    = val / mem::size_of::<Elf32_Rela>(),
+                DT_RELAENT  => rela_ent   = val,
+                DT_JMPREL   => pltrel_off = val,
+                DT_PLTRELSZ => pltrel_sz  = val / mem::size_of::<Elf32_Rela>(),
+                DT_HASH     => {
+                    nbucket  = *get_ref::<Elf32_Word>(image, val + 0)
+                                        .map_err(|()| "cannot read hash bucket count")? as usize;
+                    nchain   = *get_ref::<Elf32_Word>(image, val + 4)
+                                        .map_err(|()| "cannot read hash chain count")? as usize;
+                    hash_off = val + 8;
+                    hash_sz  = nbucket + nchain;
+                }
+                _ => ()
+            }
+        }
+
+        if sym_ent != mem::size_of::<Elf32_Sym>() {
+            return Err("incorrect symbol entry size")?
+        }
+        if rela_ent != mem::size_of::<Elf32_Rela>() {
+            return Err("incorrect relocation entry size")?
+        }
+
+        // These are the same--there are as many chains as buckets, and the chains only contain
+        // the symbols that overflowed the bucket.
+        symtab_sz = nchain;
+
+        // Drop the mutability. See also the comment below.
+        let image = &*image;
+
+        let strtab = get_ref_slice::<u8>(image, strtab_off, strtab_sz)
+                                   .map_err(|()| "cannot read string table")?;
+        let symtab = get_ref_slice::<Elf32_Sym>(image, symtab_off, symtab_sz)
+                                   .map_err(|()| "cannot read symbol table")?;
+        let rela   = get_ref_slice::<Elf32_Rela>(image, rela_off, rela_sz)
+                                   .map_err(|()| "cannot read rela entries")?;
+        let pltrel = get_ref_slice::<Elf32_Rela>(image, pltrel_off, pltrel_sz)
+                                   .map_err(|()| "cannot read pltrel entries")?;
+        let hash   = get_ref_slice::<Elf32_Word>(image, hash_off, hash_sz)
+                                   .map_err(|()| "cannot read hash entries")?;
+
+        let library = Library {
+            image_off:   image.as_ptr() as Elf32_Word,
+            image_sz:    image.len(),
+            strtab:      strtab,
+            symtab:      symtab,
+            hash_bucket: &hash[..nbucket],
+            hash_chain:  &hash[nbucket..nbucket + nchain],
+        };
+
+        // If a borrow exists anywhere, the borrowed memory cannot be mutated except
+        // through that pointer or it's UB. However, we need to retain pointers
+        // to the symbol tables and relocations, and at the same time mutate the code
+        // to resolve the relocations.
+        //
+        // To avoid invoking UB, we drop the only pointer to the entire area (which is
+        // unique since it's a &mut); we retain pointers to the various tables, but
+        // we never write to the memory they refer to, so it's safe.
+        mem::drop(image);
+
+        for r in rela   { library.fixup_rela(r, resolve)? }
+        for r in pltrel { library.fixup_rela(r, resolve)? }
+
+        Ok(library)
+    }
+}

artiq/firmware/runtime/Cargo.toml

@@ -19,6 +19,7 @@ logger_artiq = { path = "../liblogger_artiq" }
 cslice = { version = "0.3" }
 log = { version = "0.3", default-features = false, features = ["max_level_debug"] }
 board = { path = "../libboard", features = ["uart_console"] }
+dyld = { path = "../libdyld" }
 drtioaux = { path = "../libdrtioaux" }
 fringe = { version = "= 1.1.0", default-features = false, features = ["alloc"] }
 byteorder = { version = "1.0", default-features = false }

artiq/firmware/runtime/kernel_proto.rs

@@ -1,6 +1,7 @@
 #![allow(dead_code)]
 
 use core::fmt;
+use dyld;
 
 pub const KERNELCPU_EXEC_ADDRESS:    usize = 0x40800000;
 pub const KERNELCPU_PAYLOAD_ADDRESS: usize = 0x40840000;
@@ -22,7 +23,7 @@ pub struct Exception<'a> {
 #[derive(Debug)]
 pub enum Message<'a> {
     LoadRequest(&'a [u8]),
-    LoadReply(Result<(), &'a str>),
+    LoadReply(Result<(), dyld::Error<'a>>),
 
     NowInitRequest,
     NowInitReply(u64),

artiq/firmware/runtime/lib.rs

@@ -16,6 +16,7 @@ extern crate smoltcp;
 extern crate board;
 #[cfg(has_drtio)]
 extern crate drtioaux;
+extern crate dyld;
 
 use std::boxed::Box;
 use smoltcp::wire::{EthernetAddress, IpAddress};

artiq/firmware/runtime/session.rs

@@ -179,7 +179,7 @@ unsafe fn kern_load(io: &Io, session: &mut Session, library: &[u8]) -> io::Resul
                 session.kernel_state = KernelState::Loaded;
                 Ok(())
             }
-            &kern::LoadReply(Err(error)) => {
+            &kern::LoadReply(Err(ref error)) => {
                 kernel::stop();
                 Err(io::Error::new(io::ErrorKind::Other,
                                    format!("cannot load kernel: {}", error)))