Auto merge of #1284 - vakaras:add-threads-cr2, r=RalfJung

Implement basic support for concurrency (Linux/macos only)

Changes  (most new code is in `src/threads.rs` and `src/shims/foreign_items/posix.rs`):

1. Move the stack from `Machine` to a newly created `Thread` struct.
2. Add a `ThreadSet` struct that manages the threads.
3. Change `canonical_alloc_id` to create a unique allocation id for each thread local and thread (the responsible struct is `ThreadLocalStorage`)
4. Change the code to execute the thread local destructors immediately when a thread terminates.
5. Add the most basic round-robin scheduler.

This pull request depends on [these changes to the compiler](rust-lang/rust#70598).

README.md

@@ -47,7 +47,9 @@ in your program, and cannot run all programs:
 * Miri runs the program as a platform-independent interpreter, so the program
   has no access to most platform-specific APIs or FFI. A few APIs have been
   implemented (such as printing to stdout) but most have not: for example, Miri
-  currently does not support concurrency, or SIMD, or networking.
+  currently does not support SIMD or networking.
+* Miri currently does not check for data-races and most other concurrency
+  related issues.
 
 [rust]: https://www.rust-lang.org/
 [mir]: https://github.com/rust-lang/rfcs/blob/master/text/1211-mir.md

src/diagnostics.rs

@@ -139,7 +139,7 @@ fn report_msg<'tcx, 'mir>(
     mut helps: Vec<String>,
     error: bool,
 ) {
-    let span = if let Some(frame) = ecx.machine.stack.last() {
+    let span = if let Some(frame) = ecx.active_thread_stack().last() {
         frame.current_source_info().unwrap().span
     } else {
         DUMMY_SP
@@ -171,7 +171,7 @@ fn report_msg<'tcx, 'mir>(
 
     err.emit();
 
-    for (i, frame) in ecx.machine.stack.iter().enumerate() {
+    for (i, frame) in ecx.active_thread_stack().iter().enumerate() {
         trace!("-------------------");
         trace!("Frame {}", i);
         trace!("    return: {:?}", frame.return_place.map(|p| *p));

src/eval.rs

@@ -205,14 +205,24 @@ pub fn eval_main<'tcx>(tcx: TyCtxt<'tcx>, main_id: DefId, config: MiriConfig) ->
     // Perform the main execution.
     let res: InterpResult<'_, i64> = (|| {
         // Main loop.
-        while ecx.step()? {
+        loop {
+            match ecx.schedule()? {
+                SchedulingAction::ExecuteStep => {
+                    assert!(ecx.step()?, "a terminated thread was scheduled for execution");
+                }
+                SchedulingAction::ExecuteDtors => {
+                    // This will either enable the thread again (so we go back
+                    // to `ExecuteStep`), or determine that this thread is done
+                    // for good.
+                    ecx.schedule_next_tls_dtor_for_active_thread()?;
+                }
+                SchedulingAction::Stop => {
+                    break;
+                }
+            }
             ecx.process_diagnostics();
         }
-        // Read the return code pointer *before* we run TLS destructors, to assert
-        // that it was written to by the time that `start` lang item returned.
         let return_code = ecx.read_scalar(ret_place.into())?.not_undef()?.to_machine_isize(&ecx)?;
-        // Global destructors.
-        ecx.run_tls_dtors()?;
         Ok(return_code)
     })();
 

src/lib.rs

@@ -12,6 +12,7 @@ extern crate rustc_ast;
 #[macro_use] extern crate rustc_middle;
 extern crate rustc_data_structures;
 extern crate rustc_hir;
+extern crate rustc_index;
 extern crate rustc_mir;
 extern crate rustc_span;
 extern crate rustc_target;
@@ -26,6 +27,7 @@ mod operator;
 mod range_map;
 mod shims;
 mod stacked_borrows;
+mod thread;
 
 // Make all those symbols available in the same place as our own.
 pub use rustc_mir::interpret::*;
@@ -40,6 +42,7 @@ pub use crate::shims::intrinsics::EvalContextExt as IntrinsicsEvalContextExt;
 pub use crate::shims::os_str::EvalContextExt as OsStrEvalContextExt;
 pub use crate::shims::panic::{CatchUnwindData, EvalContextExt as PanicEvalContextExt};
 pub use crate::shims::sync::{EvalContextExt as SyncEvalContextExt};
+pub use crate::shims::thread::EvalContextExt as ThreadShimsEvalContextExt;
 pub use crate::shims::time::EvalContextExt as TimeEvalContextExt;
 pub use crate::shims::tls::{EvalContextExt as TlsEvalContextExt, TlsData};
 pub use crate::shims::EvalContextExt as ShimsEvalContextExt;
@@ -60,6 +63,9 @@ pub use crate::range_map::RangeMap;
 pub use crate::stacked_borrows::{
     EvalContextExt as StackedBorEvalContextExt, Item, Permission, PtrId, Stack, Stacks, Tag,
 };
+pub use crate::thread::{
+    EvalContextExt as ThreadsEvalContextExt, SchedulingAction, ThreadId, ThreadManager, ThreadState,
+};
 
 /// Insert rustc arguments at the beginning of the argument list that Miri wants to be
 /// set per default, for maximal validation power.

src/machine.rs

@@ -251,8 +251,8 @@ pub struct Evaluator<'mir, 'tcx> {
     /// The "time anchor" for this machine's monotone clock (for `Instant` simulation).
     pub(crate) time_anchor: Instant,
 
-    /// The call stack.
-    pub(crate) stack: Vec<Frame<'mir, 'tcx, Tag, FrameData<'tcx>>>,
+    /// The set of threads.
+    pub(crate) threads: ThreadManager<'mir, 'tcx>,
 
     /// Precomputed `TyLayout`s for primitive data types that are commonly used inside Miri.
     pub(crate) layouts: PrimitiveLayouts<'tcx>,
@@ -282,7 +282,7 @@ impl<'mir, 'tcx> Evaluator<'mir, 'tcx> {
             panic_payload: None,
             time_anchor: Instant::now(),
             layouts,
-            stack: Vec::default(),
+            threads: ThreadManager::default(),
         }
     }
 }
@@ -416,6 +416,14 @@ impl<'mir, 'tcx> Machine<'mir, 'tcx> for Evaluator<'mir, 'tcx> {
         Ok(())
     }
 
+    fn adjust_global_const(
+        ecx: &InterpCx<'mir, 'tcx, Self>,
+        mut val: mir::interpret::ConstValue<'tcx>,
+    ) -> InterpResult<'tcx, mir::interpret::ConstValue<'tcx>> {
+        ecx.remap_thread_local_alloc_ids(&mut val)?;
+        Ok(val)
+    }
+
     fn canonical_alloc_id(mem: &Memory<'mir, 'tcx, Self>, id: AllocId) -> AllocId {
         let tcx = mem.tcx;
         // Figure out if this is an extern static, and if yes, which one.
@@ -525,18 +533,16 @@ impl<'mir, 'tcx> Machine<'mir, 'tcx> for Evaluator<'mir, 'tcx> {
         Ok(frame.with_extra(extra))
     }
 
-    #[inline(always)]
     fn stack<'a>(
-        ecx: &'a InterpCx<'mir, 'tcx, Self>,
+        ecx: &'a InterpCx<'mir, 'tcx, Self>
     ) -> &'a [Frame<'mir, 'tcx, Self::PointerTag, Self::FrameExtra>] {
-        &ecx.machine.stack
+        ecx.active_thread_stack()
     }
 
-    #[inline(always)]
     fn stack_mut<'a>(
-        ecx: &'a mut InterpCx<'mir, 'tcx, Self>,
+        ecx: &'a mut InterpCx<'mir, 'tcx, Self>
     ) -> &'a mut Vec<Frame<'mir, 'tcx, Self::PointerTag, Self::FrameExtra>> {
-        &mut ecx.machine.stack
+        ecx.active_thread_stack_mut()
     }
 
     #[inline(always)]

src/shims/foreign_items/posix.rs

@@ -221,13 +221,15 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
             }
             "pthread_getspecific" => {
                 let key = this.force_bits(this.read_scalar(args[0])?.not_undef()?, args[0].layout.size)?;
-                let ptr = this.machine.tls.load_tls(key, this)?;
+                let active_thread = this.get_active_thread()?;
+                let ptr = this.machine.tls.load_tls(key, active_thread, this)?;
                 this.write_scalar(ptr, dest)?;
             }
             "pthread_setspecific" => {
                 let key = this.force_bits(this.read_scalar(args[0])?.not_undef()?, args[0].layout.size)?;
+                let active_thread = this.get_active_thread()?;
                 let new_ptr = this.read_scalar(args[1])?.not_undef()?;
-                this.machine.tls.store_tls(key, this.test_null(new_ptr)?)?;
+                this.machine.tls.store_tls(key, active_thread, this.test_null(new_ptr)?)?;
 
                 // Return success (`0`).
                 this.write_null(dest)?;
@@ -291,9 +293,30 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
                 this.write_scalar(Scalar::from_i32(result), dest)?;
             }
 
-            // Better error for attempts to create a thread
+            // Threading
             "pthread_create" => {
-                throw_unsup_format!("Miri does not support threading");
+                assert_eq!(args.len(), 4);
+                let result = this.pthread_create(args[0], args[1], args[2], args[3])?;
+                this.write_scalar(Scalar::from_i32(result), dest)?;
+            }
+            "pthread_join" => {
+                assert_eq!(args.len(), 2);
+                let result = this.pthread_join(args[0], args[1])?;
+                this.write_scalar(Scalar::from_i32(result), dest)?;
+            }
+            "pthread_detach" => {
+                assert_eq!(args.len(), 1);
+                let result = this.pthread_detach(args[0])?;
+                this.write_scalar(Scalar::from_i32(result), dest)?;
+            }
+            "pthread_self" => {
+                assert_eq!(args.len(), 0);
+                this.pthread_self(dest)?;
+            }
+            "sched_yield" => {
+                assert_eq!(args.len(), 0);
+                let result = this.sched_yield()?;
+                this.write_scalar(Scalar::from_i32(result), dest)?;
             }
 
             // Miscellaneous
@@ -312,15 +335,11 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
                 // We do not support forking, so there is nothing to do here.
                 this.write_null(dest)?;
             }
-            "sched_yield" => {
-                this.write_null(dest)?;
-            }
 
             // Incomplete shims that we "stub out" just to get pre-main initialization code to work.
             // These shims are enabled only when the caller is in the standard library.
             | "pthread_attr_init"
             | "pthread_attr_destroy"
-            | "pthread_self"
             | "pthread_attr_setstacksize"
             | "pthread_condattr_init"
             | "pthread_condattr_setclock"
@@ -330,6 +349,15 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
             => {
                 this.write_null(dest)?;
             }
+            "pthread_attr_getguardsize" if this.frame().instance.to_string().starts_with("std::sys::unix::")
+            => {
+                let guard_size = this.deref_operand(args[1])?;
+                let guard_size_layout = this.libc_ty_layout("size_t")?;
+                this.write_scalar(Scalar::from_uint(crate::PAGE_SIZE, guard_size_layout.size), guard_size.into())?;
+
+                // Return success (`0`).
+                this.write_null(dest)?;
+            }
 
             | "signal"
             | "sigaction"

src/shims/foreign_items/posix/linux.rs

@@ -75,6 +75,13 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
                 this.write_null(dest)?;
             }
 
+            // Threading
+            "prctl" => {
+                assert_eq!(args.len(), 5);
+                let result = this.prctl(args[0], args[1], args[2], args[3], args[4])?;
+                this.write_scalar(Scalar::from_i32(result), dest)?;
+            }
+
             // Dynamically invoked syscalls
             "syscall" => {
                 let sys_getrandom = this

src/shims/foreign_items/posix/macos.rs

@@ -82,7 +82,8 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
                 let dtor = this.read_scalar(args[0])?.not_undef()?;
                 let dtor = this.memory.get_fn(dtor)?.as_instance()?;
                 let data = this.read_scalar(args[1])?.not_undef()?;
-                this.machine.tls.set_global_dtor(dtor, data)?;
+                let active_thread = this.get_active_thread()?;
+                this.machine.tls.set_thread_dtor(active_thread, dtor, data)?;
             }
 
             // Querying system information

src/shims/foreign_items/windows.rs

@@ -144,13 +144,15 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
             }
             "TlsGetValue" => {
                 let key = u128::from(this.read_scalar(args[0])?.to_u32()?);
-                let ptr = this.machine.tls.load_tls(key, this)?;
+                let active_thread = this.get_active_thread()?;
+                let ptr = this.machine.tls.load_tls(key, active_thread, this)?;
                 this.write_scalar(ptr, dest)?;
             }
             "TlsSetValue" => {
                 let key = u128::from(this.read_scalar(args[0])?.to_u32()?);
+                let active_thread = this.get_active_thread()?;
                 let new_ptr = this.read_scalar(args[1])?.not_undef()?;
-                this.machine.tls.store_tls(key, this.test_null(new_ptr)?)?;
+                this.machine.tls.store_tls(key, active_thread, this.test_null(new_ptr)?)?;
 
                 // Return success (`1`).
                 this.write_scalar(Scalar::from_i32(1), dest)?;

src/shims/mod.rs

@@ -6,6 +6,7 @@ pub mod intrinsics;
 pub mod os_str;
 pub mod panic;
 pub mod sync;
+pub mod thread;
 pub mod time;
 pub mod tls;