miri_get_backtrace: stop supporting the v0 protocol

Author: RalfJung

src/tools/miri/src/helpers.rs

@@ -1211,22 +1211,6 @@ where
     throw_ub_format!("incorrect number of arguments: got {}, expected {}", args.len(), N)
 }
 
-/// Check that the number of args is at least the minimum what we expect.
-/// FIXME: Remove this function, use varargs and `check_min_vararg_count` instead.
-pub fn check_min_arg_count<'a, 'tcx, const N: usize>(
-    name: &'a str,
-    args: &'a [OpTy<'tcx>],
-) -> InterpResult<'tcx, &'a [OpTy<'tcx>; N]> {
-    if let Some((ops, _)) = args.split_first_chunk() {
-        return interp_ok(ops);
-    }
-    throw_ub_format!(
-        "incorrect number of arguments for `{name}`: got {}, expected at least {}",
-        args.len(),
-        N
-    )
-}
-
 /// Check that the number of varargs is at least the minimum what we expect.
 /// Fixed args should not be included.
 /// Use `check_vararg_fixed_arg_count` to extract the varargs slice from full function arguments.

src/tools/miri/src/shims/backtrace.rs

@@ -4,7 +4,6 @@ use rustc_middle::ty::{self, Instance, Ty};
 use rustc_span::{BytePos, Loc, Symbol, hygiene};
 use rustc_target::callconv::{Conv, FnAbi};
 
-use crate::helpers::check_min_arg_count;
 use crate::*;
 
 impl<'tcx> EvalContextExt<'tcx> for crate::MiriInterpCx<'tcx> {}
@@ -34,13 +33,15 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
         abi: &FnAbi<'tcx, Ty<'tcx>>,
         link_name: Symbol,
         args: &[OpTy<'tcx>],
-        dest: &MPlaceTy<'tcx>,
     ) -> InterpResult<'tcx> {
         let this = self.eval_context_mut();
-        let tcx = this.tcx;
+        let ptr_ty = this.machine.layouts.mut_raw_ptr.ty;
+        let ptr_layout = this.layout_of(ptr_ty)?;
+
+        let [flags, buf] = this.check_shim(abi, Conv::Rust, link_name, args)?;
 
-        let [flags] = check_min_arg_count("miri_get_backtrace", args)?;
         let flags = this.read_scalar(flags)?.to_u64()?;
+        let buf_place = this.deref_pointer_as(buf, ptr_layout)?;
 
         let mut data = Vec::new();
         for frame in this.active_thread_stack().iter().rev() {
@@ -63,43 +64,18 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
             })
             .collect();
 
-        let len: u64 = ptrs.len().try_into().unwrap();
-
-        let ptr_ty = this.machine.layouts.mut_raw_ptr.ty;
-        let array_layout = this.layout_of(Ty::new_array(tcx.tcx, ptr_ty, len)).unwrap();
-
         match flags {
-            // storage for pointers is allocated by miri
-            // deallocating the slice is undefined behavior with a custom global allocator
             0 => {
-                let [_flags] = this.check_shim(abi, Conv::Rust, link_name, args)?;
-
-                let alloc = this.allocate(array_layout, MiriMemoryKind::Rust.into())?;
-
-                // Write pointers into array
-                for (i, ptr) in ptrs.into_iter().enumerate() {
-                    let place = this.project_index(&alloc, i as u64)?;
-
-                    this.write_pointer(ptr, &place)?;
-                }
-
-                this.write_immediate(Immediate::new_slice(alloc.ptr(), len, this), dest)?;
+                throw_unsup_format!("miri_get_backtrace: v0 is not supported any more");
             }
-            // storage for pointers is allocated by the caller
-            1 => {
-                let [_flags, buf] = this.check_shim(abi, Conv::Rust, link_name, args)?;
-
-                let ptr_layout = this.layout_of(ptr_ty)?;
-                let buf_place = this.deref_pointer_as(buf, ptr_layout)?;
-
+            1 =>
                 for (i, ptr) in ptrs.into_iter().enumerate() {
                     let offset = ptr_layout.size.checked_mul(i.try_into().unwrap(), this).unwrap();
 
                     let op_place = buf_place.offset(offset, ptr_layout, this)?;
 
                     this.write_pointer(ptr, &op_place)?;
-                }
-            }
+                },
             _ => throw_unsup_format!("unknown `miri_get_backtrace` flags {}", flags),
         };
 

src/tools/miri/src/shims/foreign_items.rs

@@ -357,7 +357,7 @@ trait EvalContextExtPriv<'tcx>: crate::MiriInterpCxExt<'tcx> {
             // Obtains a Miri backtrace. See the README for details.
             "miri_get_backtrace" => {
                 // `check_shim` happens inside `handle_miri_get_backtrace`.
-                this.handle_miri_get_backtrace(abi, link_name, args, dest)?;
+                this.handle_miri_get_backtrace(abi, link_name, args)?;
             }
             // Resolves a Miri backtrace frame. See the README for details.
             "miri_resolve_frame" => {

src/tools/miri/tests/fail/shims/backtrace/bad-backtrace-decl.rs

@@ -1,10 +1,13 @@
 extern "Rust" {
-    fn miri_get_backtrace(flags: u64) -> Box<[*mut ()]>;
+    fn miri_backtrace_size(flags: u64) -> usize;
+    fn miri_get_backtrace(flags: u64, buf: *mut *mut ());
     fn miri_resolve_frame(ptr: *mut (), flags: u64);
 }
 
 fn main() {
-    let frames = unsafe { miri_get_backtrace(0) };
+    let size = unsafe { miri_backtrace_size(0) };
+    let mut frames = vec![std::ptr::null_mut(); size];
+    unsafe { miri_get_backtrace(1, frames.as_mut_ptr()) };
     for frame in frames.iter() {
         unsafe {
             miri_resolve_frame(*frame, 0); //~ ERROR: Undefined Behavior: bad declaration of miri_resolve_frame - should return a struct with 5 fields