Can show operands at runtime when 'attempt to multiply with overflow' panic ?

[ghost]

Is it possible to show the two operands at runtime when this panic occurs ? thread 'main' panicked at 'attempt to multiply with overflow', src/main.rs:7 So maybe we can see 2*122 in the panic message?

example code

code with backtrace

output

```rust Compiling playground v0.0.1 (file:///playground) Finished dev [unoptimized + debuginfo] target(s) in 0.62 secs Running `target/debug/playground` thread 'main' panicked at 'attempt to multiply with overflow', src/main.rs:9:20 stack backtrace: 0: std::sys::imp::backtrace::tracing::imp::unwind_backtrace at /checkout/src/libstd/sys/unix/backtrace/tracing/gcc_s.rs:49 1: std::sys_common::backtrace::_print at /checkout/src/libstd/sys_common/backtrace.rs:71 2: std::panicking::default_hook::{{closure}} at /checkout/src/libstd/sys_common/backtrace.rs:60 at /checkout/src/libstd/panicking.rs:380 3: std::panicking::default_hook at /checkout/src/libstd/panicking.rs:396 4: std::panicking::rust_panic_with_hook at /checkout/src/libstd/panicking.rs:610 5: std::panicking::begin_panic at /checkout/src/libstd/panicking.rs:571 6: std::panicking::begin_panic_fmt at /checkout/src/libstd/panicking.rs:521 7: rust_begin_unwind at /checkout/src/libstd/panicking.rs:497 8: core::panicking::panic_fmt at /checkout/src/libcore/panicking.rs:71 9: core::panicking::panic at /checkout/src/libcore/panicking.rs:51 10: playground::main at src/main.rs:9 11: __rust_maybe_catch_panic at /checkout/src/libpanic_unwind/lib.rs:98 12: std::rt::lang_start at /checkout/src/libstd/panicking.rs:458 at /checkout/src/libstd/panic.rs:361 at /checkout/src/libstd/rt.rs:61 13: main 14: __libc_start_main 15: _start ```

---

EDIT: what I tried and had no effect whatsoever:

diff --git a/src/librustc_const_math/int.rs b/src/librustc_const_math/int.rs
index 65471416e8..1c05352aec 100644
--- a/src/librustc_const_math/int.rs
+++ b/src/librustc_const_math/int.rs
@@ -329,7 +329,10 @@ impl ::std::fmt::Display for ConstInt {
 macro_rules! overflowing {
     ($e:expr, $err:expr) => {{
         if $e.1 {
-            return Err(Overflow($err));
+            return {
+                eprintln!("!!!moo3:{:?}!{:?}!",$e,$err);
+                Err(Overflow($err))
+            }
         } else {
             $e.0
         }
@@ -341,6 +344,7 @@ macro_rules! impl_binop {
         impl ::std::ops::$op for ConstInt {
             type Output = Result<Self, ConstMathErr>;
             fn $func(self, rhs: Self) -> Result<Self, ConstMathErr> {
+                eprintln!("!!!moo4:{:?}!{:?}!",self,rhs);
                 match (self, rhs) {
                     (I8(a), I8(b)) => a.$checked_func(b).map(I8),
                     (I16(a), I16(b)) => a.$checked_func(b).map(I16),
@@ -428,7 +432,10 @@ fn check_division(
         (Usize(_), Usize(Us32(0))) => Err(zerr),
         (Usize(_), Usize(Us64(0))) => Err(zerr),

-        (I8(::std::i8::MIN), I8(-1)) => Err(Overflow(op)),
+        (I8(::std::i8::MIN), I8(-1)) => {
+            eprintln!("!!!moo2{:?}!",op);
+            Err(Overflow(op))
+        },
         (I16(::std::i16::MIN), I16(-1)) => Err(Overflow(op)),
         (I32(::std::i32::MIN), I32(-1)) => Err(Overflow(op)),
         (I64(::std::i64::MIN), I64(-1)) => Err(Overflow(op)),
diff --git a/src/librustc_mir/build/expr/as_rvalue.rs b/src/librustc_mir/build/expr/as_rvalue.rs
index 2512291f1a..f8fd8315c5 100644
--- a/src/librustc_mir/build/expr/as_rvalue.rs
+++ b/src/librustc_mir/build/expr/as_rvalue.rs
@@ -285,6 +285,7 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
                     bug!("MIR build_binary_op: {:?} is not checkable", op)
                 }
             });
+            eprintln!("!!!moo{:?}!",err);

             block = self.assert(block, Operand::Consume(of), false,
                                 AssertMessage::Math(err), span);

diff --git a/src/librustc_trans/mir/constant.rs b/src/librustc_trans/mir/constant.rs
index 53469689bc..783aea003d 100644
--- a/src/librustc_trans/mir/constant.rs
+++ b/src/librustc_trans/mir/constant.rs
@@ -932,6 +932,7 @@ pub fn const_scalar_checked_binop<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
                 bug!("Operator `{:?}` is not a checkable operator", op)
             }
         };
+        eprintln!("!!!moo5:{:?}!", result);

         let of = match result {
             Ok(_) => false,

[TimNN]

Regarding your patch: rustc's const evaluator has nothing whatsoever to do with the runtime panic message: Instead, when in debug mode, rustc will insert overflow checks for every multiplication / addition / subtraction.

[ghost]

Thanks @TimNN ! Any idea where to look for the code that inserts overflow checks?

So I tried this: ```rust CheckedBinaryOp(bin_op, ref left, ref right) => { // Due to the extra boolean in the result, we can never reuse the `dest.layout`. let left = self.read_immediate(self.eval_operand(left, None)?)?; let layout = if binop_right_homogeneous(bin_op) { Some(left.layout) } else { None }; let right = self.read_immediate(self.eval_operand(right, layout)?)?; self.binop_with_overflow( bin_op, left, right, dest, )?; eprintln!("!{:?}!{:?}!{:?}!{:?}!", left,bin_op,right,dest); } ``` in `interpret/step.rs` but I see no output from that `eprintln!` with this: ```rust fn main() { //let innum: i8 = 122; let in_num:i8=122; let a = 2_i8.checked_mul(in_num); let b= 2_i8.overflowing_mul(in_num); println!("{:?} / {:?}", a, b); println!("{:?}", 2*in_num); let c:i8=2*in_num; } ``` (used stage1 compiler, meanwhile rustc (stage2?) is still compiling) there are output from that `eprintln!` while it's still compiling, one example for `!Mul!`: ```rust !ImmTy { immediate: Scalar(Scalar(Bits { size: 8, bits: 16 })), layout: TyLayout { ty: usize, details: LayoutDetails { variants: Single { index: 0 }, fields: Union(0), abi: Scalar(Scalar { value: Int(I64, false), valid_range: 0..=18446744073709551615 }), align: AbiAndPrefAlign { abi: Align { pow2: 3 }, pref: Align { pow2: 3 } }, size: Size { raw: 8 } } } }!Mul!ImmTy { immediate: Scalar(Scalar(Bits { size: 8, bits: 16 })), layout: TyLayout { ty: usize, details: LayoutDetails { variants: Single { index: 0 }, fields: Union(0), abi: Scalar(Scalar { value: Int(I64, false), valid_range: 0..=18446744073709551615 }), align: AbiAndPrefAlign { abi: Align { pow2: 3 }, pref: Align { pow2: 3 } }, size: Size { raw: 8 } } } }!PlaceTy { place: Local { frame: 0, local: _1 }, layout: TyLayout { ty: (usize, bool), details: LayoutDetails { variants: Single { index: 0 }, fields: Arbitrary { offsets: [Size { raw: 0 }, Size { raw: 8 }], memory_index: [0, 1] }, abi: ScalarPair(Scalar { value: Int(I64, false), valid_range: 0..=18446744073709551615 }, Scalar { value: Int(I8, false), valid_range: 0..=1 }), align: AbiAndPrefAlign { abi: Align { pow2: 3 }, pref: Align { pow2: 3 } }, size: Size { raw: 16 } } } }! ``` but the above would've shown me a true/false somewhere in `dest`(likely this `Scalar { value: Int(I8, false), valid_range: 0..=1 })` seen above) as per this: ```rust /// Applies the binary operation `op` to the two operands and writes a tuple of the result /// and a boolean signifying the potential overflow to the destination. pub fn binop_with_overflow( &mut self, op: mir::BinOp, left: ImmTy<'tcx, M::PointerTag>, right: ImmTy<'tcx, M::PointerTag>, dest: PlaceTy<'tcx, M::PointerTag>, ) -> EvalResult<'tcx> { let (val, overflowed) = self.binary_op_imm(op, left, right)?; let val = Immediate::ScalarPair(val.into(), Scalar::from_bool(overflowed).into()); self.write_immediate(val, dest) } ``` I'm still not sure exactly where, since I don't understand most of what's going on :D But there are still more places to look: ```rust /home/xftroxgpx/build/2nonpkgs/rust.stuff/rust/rust $ grep -nrIFw CheckedBinaryOp src/librustc/ich/impls_mir.rs:347: mir::Rvalue::CheckedBinaryOp(op, ref operand1, ref operand2) => { src/librustc/mir/tcx.rs:238: Rvalue::CheckedBinaryOp(op, ref lhs, ref rhs) => { src/librustc/mir/mod.rs:2191: CheckedBinaryOp(BinOp, Operand<'tcx>, Operand<'tcx>), src/librustc/mir/mod.rs:2330: CheckedBinaryOp(ref op, ref a, ref b) => { src/librustc/mir/mod.rs:3318: CheckedBinaryOp(op, ref rhs, ref lhs) => { src/librustc/mir/mod.rs:3319: CheckedBinaryOp(op, rhs.fold_with(folder), lhs.fold_with(folder)) src/librustc/mir/mod.rs:3355: BinaryOp(_, ref rhs, ref lhs) | CheckedBinaryOp(_, ref rhs, ref lhs) => { src/librustc/mir/visit.rs:626: Rvalue::CheckedBinaryOp(_bin_op, src/librustc_mir/borrow_check/nll/type_check/mod.rs:2005: | Rvalue::CheckedBinaryOp(..) src/librustc_mir/borrow_check/nll/type_check/mod.rs:2022: | Rvalue::CheckedBinaryOp(..) src/librustc_mir/borrow_check/nll/invalidation.rs:371: | Rvalue::CheckedBinaryOp(_bin_op, ref operand1, ref operand2) => { src/librustc_mir/borrow_check/mod.rs:1206: | Rvalue::CheckedBinaryOp(_bin_op, ref operand1, ref operand2) => { src/librustc_mir/build/expr/as_rvalue.rs:416: Rvalue::CheckedBinaryOp(op, lhs, rhs), src/librustc_mir/dataflow/move_paths/builder.rs:309: Rvalue::CheckedBinaryOp(ref _binop, ref lhs, ref rhs) => { src/librustc_mir/interpret/step.rs:163: CheckedBinaryOp(bin_op, ref left, ref right) => { src/librustc_mir/transform/lower_128bit.rs:75: | Rvalue::CheckedBinaryOp(_, lhs, rhs) => (place, lhs, rhs), src/librustc_mir/transform/lower_128bit.rs:157: StatementKind::Assign(_, box Rvalue::CheckedBinaryOp(bin_op, ref lhs, _)) => { src/librustc_mir/transform/const_prop.rs:399: Rvalue::CheckedBinaryOp(op, ref left, ref right) | src/librustc_mir/transform/const_prop.rs:454: let val = if let Rvalue::CheckedBinaryOp(..) = *rvalue { src/librustc_mir/transform/qualify_consts.rs:586: Rvalue::CheckedBinaryOp(..) | src/librustc_mir/transform/qualify_min_const_fn.rs:172: Rvalue::BinaryOp(_, lhs, rhs) | Rvalue::CheckedBinaryOp(_, lhs, rhs) => { src/librustc_codegen_ssa/mir/rvalue.rs:435: mir::Rvalue::CheckedBinaryOp(op, ref lhs, ref rhs) => { src/librustc_codegen_ssa/mir/rvalue.rs:716: mir::Rvalue::CheckedBinaryOp(..) | ``` I put an `eprintln!` and got no output: ```rust /// Applies the binary operation `op` to the two operands and writes a tuple of the result /// and a boolean signifying the potential overflow to the destination. pub fn binop_with_overflow( &mut self, op: mir::BinOp, left: ImmTy<'tcx, M::PointerTag>, right: ImmTy<'tcx, M::PointerTag>, dest: PlaceTy<'tcx, M::PointerTag>, ) -> EvalResult<'tcx> { let (val, overflowed) = self.binary_op_imm(op, left, right)?; let val = Immediate::ScalarPair(val.into(), Scalar::from_bool(overflowed).into()); eprintln!("{:?}",val); self.write_immediate(val, dest) } ``` in `interpret/operator.rs` maybe i'm looking in the wrong place!

ok, i might be on to something, with this patch: ```rust diff --git a/src/librustc/mir/interpret/error.rs b/src/librustc/mir/interpret/error.rs index c3fe5d773a..f8c87f3393 100644 --- a/src/librustc/mir/interpret/error.rs +++ b/src/librustc/mir/interpret/error.rs @@ -413,7 +413,25 @@ impl<'tcx, O> EvalErrorKind<'tcx, O> { "referenced constant has errors", Overflow(mir::BinOp::Add) => "attempt to add with overflow", Overflow(mir::BinOp::Sub) => "attempt to subtract with overflow", - Overflow(mir::BinOp::Mul) => "attempt to multiply with overflow", + Overflow(mir::BinOp::Mul) => { + //sys_common::backtrace::print(, PrintFormat::Short); + //extern crate sys;//HOW to?! + //use sys::backtrace; + //extern crate backtrace; + //use backtrace; + //#[cfg(feature = "backtrace")] //this is never true here! + { + //extern crate sys_common; + //use sys_common::rwlock::RWLock; + //use sys_common::thread_info; + //use sys_common::util; + //use sys_common::backtrace; + use backtrace::Backtrace; + eprintln!("{:?}", Backtrace::new()); //thanks to WindowsBunny on irc for the idea! + } + "wuuuuuuattttttt??!attempt to multiply with overflow" + } + , Overflow(mir::BinOp::Div) => "attempt to divide with overflow", Overflow(mir::BinOp::Rem) => "attempt to calculate the remainder with overflow", OverflowNeg => "attempt to negate with overflow", ``` I'm getting the stacktrace during compile-only, for this program: ```rust fn main() { // let in_num:i32=1289346750; // 4CD9DEBE // println!("{:?}", 2*in_num); //let innum: i8 = 122; let in_num:i8=122; //let a = 2_i8.checked_mul(in_num); let a=0; //let b= 2_i8.overflowing_mul(in_num); let b=0; println!("{:?} / {:?}", a, b); let _c:i8=2*in_num; //println!("{:?}", 2*in_num); } ``` looks like this: ```rust /tmp/tr $ time /home/xftroxgpx/build/2nonpkgs/rust.stuff/rust/rust/build/x86_64-unknown-linux-gnu/stage1/bin/rustc --edition=2018 -C debuginfo=2 /tmp/tr/src/main.rs -v && RUST_LOG=trace RUST_BACKTRACE=1 ./main stack backtrace: 0: >::description::h93cabbaeb77cf8e9 (0x7ff4add1b014) at /home/xftroxgpx/build/2nonpkgs/rust.stuff/rust/rust/src/librustc/mir/interpret/error.rs:430 1: rustc_codegen_ssa::mir::block::>::codegen_terminator::hf5867a49a7c0092c (0x7ff4ade85850) at /home/xftroxgpx/build/2nonpkgs/rust.stuff/rust/rust/src/librustc_codegen_ssa/mir/block.rs:396 2: rustc_codegen_ssa::mir::block::>::codegen_block::hd71f5a610ab19665 (0x7ff4ade821fe) at /home/xftroxgpx/build/2nonpkgs/rust.stuff/rust/rust/src/librustc_codegen_ssa/mir/block.rs:38 rustc_codegen_ssa::mir::codegen_mir::h97380ecbeb32f317 at /home/xftroxgpx/build/2nonpkgs/rust.stuff/rust/rust/src/librustc_codegen_ssa/mir/mod.rs:343 3: rustc_codegen_ssa::base::codegen_instance::h08fe7402fba94e2a (0x7ff4add0c5d2) at /home/xftroxgpx/build/2nonpkgs/rust.stuff/rust/rust/src/librustc_codegen_ssa/base.rs:436 4: rustc_codegen_ssa::mono_item::MonoItemExt::define::hc1b44ea0cbf6e3a8 (0x7ff4adda9047) at /home/xftroxgpx/build/2nonpkgs/rust.stuff/rust/rust/src/librustc_codegen_ssa/mono_item.rs:43 5: rustc_codegen_llvm::base::compile_codegen_unit::module_codegen::he0cfdc914df0c847 (0x7ff4addbe1bd) at src/librustc_codegen_llvm/base.rs:178 6: rustc::dep_graph::graph::DepGraph::with_task_impl::h8ca210522f66e976 (0x7ff4ade33d9c) at /home/xftroxgpx/build/2nonpkgs/rust.stuff/rust/rust/src/librustc/dep_graph/graph.rs:295 rustc::dep_graph::graph::DepGraph::with_task::h9677e9916ca4c2fb at /home/xftroxgpx/build/2nonpkgs/rust.stuff/rust/rust/src/librustc/dep_graph/graph.rs:181 7: rustc_codegen_llvm::base::compile_codegen_unit::h2c505b8e6ff00db0 (0x7ff4addbddfa) at src/librustc_codegen_llvm/base.rs:145 8: ::compile_codegen_unit::h92d011270b11d0bf (0x7ff4adc16af1) at src/librustc_codegen_llvm/lib.rs:144 9: rustc_codegen_ssa::base::codegen_crate::hdac3c97bf6d7fbca (0x7ff4add0a243) at /home/xftroxgpx/build/2nonpkgs/rust.stuff/rust/rust/src/librustc_codegen_ssa/base.rs:687 10: ::codegen_crate::h888e69a0f96218ba (0x7ff4adc170d0) at src/librustc_codegen_llvm/lib.rs:304 11: rustc_driver::driver::phase_4_codegen::{{closure}}::h227d1332dd6978c2 (0x7ff4bccf2cdc) at src/librustc_driver/driver.rs:1349 rustc::util::common::time_ext::h194714b7b1369f7c at /home/xftroxgpx/build/2nonpkgs/rust.stuff/rust/rust/src/librustc/util/common.rs:150 rustc::util::common::time::ha11a3c04898eac7a at /home/xftroxgpx/build/2nonpkgs/rust.stuff/rust/rust/src/librustc/util/common.rs:144 12: rustc_driver::driver::phase_4_codegen::h6bcca110e885caa9 (0x7ff4bcce18e0) at src/librustc_driver/driver.rs:1349 13: rustc_driver::driver::compile_input::{{closure}}::h231c43f5b8e6c3e9 (0x7ff4bcdf8c50) at src/librustc_driver/driver.rs:316 14: rustc_driver::driver::phase_3_run_analysis_passes::{{closure}}::h8f36925bf5962022 (0x7ff4bcdf2b0d) at src/librustc_driver/driver.rs:1332 rustc::ty::context::tls::enter_global::{{closure}}::{{closure}}::hef4ec43c7065bde2 at /home/xftroxgpx/build/2nonpkgs/rust.stuff/rust/rust/src/librustc/ty/context.rs:1963 rustc::ty::context::tls::enter_context::{{closure}}::he652dca2629d0c4f at /home/xftroxgpx/build/2nonpkgs/rust.stuff/rust/rust/src/librustc/ty/context.rs:1929 rustc_rayon_core::tlv::with::h1749e7b1cef75566 at /home/xftroxgpx/.cargo/registry/src/github.com-1ecc6299db9ec823/rustc-rayon-core-0.1.1/src/tlv.rs:19 15: rustc::ty::context::tls::set_tlv::hc87f5ce672c3fe3c (0x7ff4bcc8a35f) at /home/xftroxgpx/build/2nonpkgs/rust.stuff/rust/rust/src/librustc/ty/context.rs:1838 rustc::ty::context::tls::enter_context::h540c161a5c470d51 at /home/xftroxgpx/build/2nonpkgs/rust.stuff/rust/rust/src/librustc/ty/context.rs:1928 rustc::ty::context::tls::enter_global::{{closure}}::h79bd1d338d355e69 at /home/xftroxgpx/build/2nonpkgs/rust.stuff/rust/rust/src/librustc/ty/context.rs:1962 rustc::ty::context::tls::with_thread_locals::{{closure}}::{{closure}}::h36513f108ba283a4 at /home/xftroxgpx/build/2nonpkgs/rust.stuff/rust/rust/src/librustc/ty/context.rs:1917 >::try_with::hb5b48892a35874da at /home/xftroxgpx/build/2nonpkgs/rust.stuff/rust/rust/src/libstd/thread/local.rs:299 >::with::hb27a948451c920d5 at /home/xftroxgpx/build/2nonpkgs/rust.stuff/rust/rust/src/libstd/thread/local.rs:245 rustc::ty::context::tls::with_thread_locals::{{closure}}::hb1b4ea8acb560389 at /home/xftroxgpx/build/2nonpkgs/rust.stuff/rust/rust/src/librustc/ty/context.rs:1909 >::try_with::hfee4f67c590f43fa at /home/xftroxgpx/build/2nonpkgs/rust.stuff/rust/rust/src/libstd/thread/local.rs:299 >::with::hf7d2ceb7d643b7ad at /home/xftroxgpx/build/2nonpkgs/rust.stuff/rust/rust/src/libstd/thread/local.rs:245 16: rustc::ty::context::tls::with_thread_locals::hc28c29965271ab67 (0x7ff4bcd721e4) at /home/xftroxgpx/build/2nonpkgs/rust.stuff/rust/rust/src/librustc/ty/context.rs:1901 rustc::ty::context::tls::enter_global::h72db5c2568d3abbb at /home/xftroxgpx/build/2nonpkgs/rust.stuff/rust/rust/src/librustc/ty/context.rs:1940 17: rustc::ty::context::TyCtxt::create_and_enter::h26fa6283efd9a6b7 (0x7ff4bcd8c37d) at /home/xftroxgpx/build/2nonpkgs/rust.stuff/rust/rust/src/librustc/ty/context.rs:1260 18: rustc_driver::driver::phase_3_run_analysis_passes::he0bcbc46efa21744 (0x7ff4bcd03052) at src/librustc_driver/driver.rs:1229 19: rustc_driver::driver::compile_input::h4d4398317b2c6d58 (0x7ff4bccdfb97) at src/librustc_driver/driver.rs:275 20: rustc_driver::run_compiler_with_pool::he0ab58fb4a355771 (0x7ff4bce01fac) at src/librustc_driver/lib.rs:527 21: rustc_driver::run_compiler::{{closure}}::h1e4c126fef6bd8dc (0x7ff4bcd9fa05) at src/librustc_driver/lib.rs:449 rustc_driver::driver::spawn_thread_pool::{{closure}}::{{closure}}::hd8a1f072d8753d2c at src/librustc_driver/driver.rs:86 rustc_rayon_core::thread_pool::ThreadPool::install::{{closure}}::h7a43dce80642a2b4 at /home/xftroxgpx/.cargo/registry/src/github.com-1ecc6299db9ec823/rustc-rayon-core-0.1.1/src/thread_pool/mod.rs:158 rustc_rayon_core::registry::Registry::in_worker_cold::{{closure}}::he1599453f909cbdd at /home/xftroxgpx/.cargo/registry/src/github.com-1ecc6299db9ec823/rustc-rayon-core-0.1.1/src/registry.rs:359 as rustc_rayon_core::job::Job>::execute::{{closure}}::hc7a75fba1110d7b4 at /home/xftroxgpx/.cargo/registry/src/github.com-1ecc6299db9ec823/rustc-rayon-core-0.1.1/src/job.rs:121 as core::ops::function::FnOnce<()>>::call_once::h0fe22c82f5272699 at /home/xftroxgpx/build/2nonpkgs/rust.stuff/rust/rust/src/libstd/panic.rs:309 22: std::panicking::try::do_call::hb69d76ef89a9d93d (0x7ff4bcd74e53) at /home/xftroxgpx/build/2nonpkgs/rust.stuff/rust/rust/src/libstd/panicking.rs:297 23: __rust_maybe_catch_panic (0x7ff4bcbb7ff0) at src/libpanic_unwind/lib.rs:92 24: std::panicking::try::hfe22bc5b1e02df82 (0x7ff4bcd74aae) at /home/xftroxgpx/build/2nonpkgs/rust.stuff/rust/rust/src/libstd/panicking.rs:276 25: std::panic::catch_unwind::hab370608fba46ba6 (0x7ff4bcda25f8) at /home/xftroxgpx/build/2nonpkgs/rust.stuff/rust/rust/src/libstd/panic.rs:388 26: rustc_rayon_core::unwind::halt_unwinding::hee06b0c95c109e81 (0x7ff4bcc9a478) at /home/xftroxgpx/.cargo/registry/src/github.com-1ecc6299db9ec823/rustc-rayon-core-0.1.1/src/unwind.rs:18 27: as rustc_rayon_core::job::Job>::execute::h693c3cfaa60523e8 (0x7ff4bcd1d4f0) at /home/xftroxgpx/.cargo/registry/src/github.com-1ecc6299db9ec823/rustc-rayon-core-0.1.1/src/job.rs:121 28: rustc_rayon_core::job::JobRef::execute::ha52f551ecea678cd (0x7ff4b8702df3) at /home/xftroxgpx/.cargo/registry/src/github.com-1ecc6299db9ec823/rustc-rayon-core-0.1.1/src/job.rs:62 rustc_rayon_core::registry::WorkerThread::execute::hc89f8cf7c1d41e9b at /home/xftroxgpx/.cargo/registry/src/github.com-1ecc6299db9ec823/rustc-rayon-core-0.1.1/src/registry.rs:609 rustc_rayon_core::registry::WorkerThread::wait_until_cold::h5177fb21147a739c at /home/xftroxgpx/.cargo/registry/src/github.com-1ecc6299db9ec823/rustc-rayon-core-0.1.1/src/registry.rs:589 29: rustc_rayon_core::registry::WorkerThread::wait_until::h12fac8c0f1ed4bb8 (0x7ff4b87039db) at /home/xftroxgpx/.cargo/registry/src/github.com-1ecc6299db9ec823/rustc-rayon-core-0.1.1/src/registry.rs:565 rustc_rayon_core::registry::main_loop::{{closure}}::hb6a51d03c20496ef at /home/xftroxgpx/.cargo/registry/src/github.com-1ecc6299db9ec823/rustc-rayon-core-0.1.1/src/registry.rs:701 30: rustc_driver::driver::spawn_thread_pool::{{closure}}::{{closure}}::{{closure}}::{{closure}}::{{closure}}::{{closure}}::{{closure}}::h41edfded97a513b4 (0x7ff4bce0b6df) at src/librustc_driver/driver.rs:100 >::set::hb491eb13ee4c3b95 at /home/xftroxgpx/.cargo/registry/src/github.com-1ecc6299db9ec823/scoped-tls-0.1.2/src/lib.rs:155 31: rustc_driver::driver::spawn_thread_pool::{{closure}}::{{closure}}::{{closure}}::{{closure}}::{{closure}}::{{closure}}::he70cf8f3dbad9ef5 (0x7ff4bcc8629b) at src/librustc_driver/driver.rs:99 rustc::ty::context::tls::with_thread_locals::{{closure}}::{{closure}}::h6074966d5788cc51 at /home/xftroxgpx/build/2nonpkgs/rust.stuff/rust/rust/src/librustc/ty/context.rs:1917 >::try_with::h077abb1178ec3502 at /home/xftroxgpx/build/2nonpkgs/rust.stuff/rust/rust/src/libstd/thread/local.rs:299 >::with::he2ee3cda01983d7a at /home/xftroxgpx/build/2nonpkgs/rust.stuff/rust/rust/src/libstd/thread/local.rs:245 rustc::ty::context::tls::with_thread_locals::{{closure}}::h01bfe6c1c47008ff at /home/xftroxgpx/build/2nonpkgs/rust.stuff/rust/rust/src/librustc/ty/context.rs:1909 >::try_with::h4fcbc8d2e276cb37 at /home/xftroxgpx/build/2nonpkgs/rust.stuff/rust/rust/src/libstd/thread/local.rs:299 >::with::h07c04aa6c28bd983 at /home/xftroxgpx/build/2nonpkgs/rust.stuff/rust/rust/src/libstd/thread/local.rs:245 32: rustc_driver::driver::spawn_thread_pool::{{closure}}::{{closure}}::{{closure}}::{{closure}}::{{closure}}::h6a1d65875583578a (0x7ff4bce0b776) at src/librustc_driver/driver.rs:98 >::set::h385c43b72356bc8f at /home/xftroxgpx/.cargo/registry/src/github.com-1ecc6299db9ec823/scoped-tls-0.1.2/src/lib.rs:155 rustc_driver::driver::spawn_thread_pool::{{closure}}::{{closure}}::{{closure}}::{{closure}}::h597bf30d030c4095 at src/librustc_driver/driver.rs:97 >::set::hc0e454a26a369f5e at /home/xftroxgpx/.cargo/registry/src/github.com-1ecc6299db9ec823/scoped-tls-0.1.2/src/lib.rs:155 33: rustc_driver::driver::spawn_thread_pool::{{closure}}::{{closure}}::{{closure}}::he26ea67043a46132 (0x7ff4bce1976d) at src/librustc_driver/driver.rs:96 rustc_rayon_core::thread_pool::ThreadPool::scoped_pool::{{closure}}::ha394f83af0bf888f at /home/xftroxgpx/.cargo/registry/src/github.com-1ecc6299db9ec823/rustc-rayon-core-0.1.1/src/thread_pool/mod.rs:103 34: __rust_maybe_catch_panic (0x7ff4bcbb7ff0) at src/libpanic_unwind/lib.rs:92 35: std::panicking::try::h0324edf9a21513db (0x7ff4b86fcf5f) at /home/xftroxgpx/build/2nonpkgs/rust.stuff/rust/rust/src/libstd/panicking.rs:276 std::panic::catch_unwind::hac46a414d53b9e0d at /home/xftroxgpx/build/2nonpkgs/rust.stuff/rust/rust/src/libstd/panic.rs:388 rustc_rayon_core::unwind::halt_unwinding::h2b6105fb03509a92 at /home/xftroxgpx/.cargo/registry/src/github.com-1ecc6299db9ec823/rustc-rayon-core-0.1.1/src/unwind.rs:18 rustc_rayon_core::registry::main_loop::h1fda886cbb064140 at /home/xftroxgpx/.cargo/registry/src/github.com-1ecc6299db9ec823/rustc-rayon-core-0.1.1/src/registry.rs:705 rustc_rayon_core::registry::Registry::new::{{closure}}::hdc57e38d2eea6137 at /home/xftroxgpx/.cargo/registry/src/github.com-1ecc6299db9ec823/rustc-rayon-core-0.1.1/src/registry.rs:139 std::sys_common::backtrace::__rust_begin_short_backtrace::h3ee2e7302fbd8cab at /home/xftroxgpx/build/2nonpkgs/rust.stuff/rust/rust/src/libstd/sys_common/backtrace.rs:135 36: std::thread::Builder::spawn_unchecked::{{closure}}::{{closure}}::h4d46a00a4516e335 (0x7ff4b86fddfb) at /home/xftroxgpx/build/2nonpkgs/rust.stuff/rust/rust/src/libstd/thread/mod.rs:469 as core::ops::function::FnOnce<()>>::call_once::h88071d6ae379fc37 at /home/xftroxgpx/build/2nonpkgs/rust.stuff/rust/rust/src/libstd/panic.rs:309 std::panicking::try::do_call::hd9ecda59b94bddcc at /home/xftroxgpx/build/2nonpkgs/rust.stuff/rust/rust/src/libstd/panicking.rs:297 37: __rust_maybe_catch_panic (0x7ff4bcbb7ff0) at src/libpanic_unwind/lib.rs:92 38: std::panicking::try::h3d46a5104c396178 (0x7ff4b870035f) at /home/xftroxgpx/build/2nonpkgs/rust.stuff/rust/rust/src/libstd/panicking.rs:276 std::panic::catch_unwind::hc10ac859fe269334 at /home/xftroxgpx/build/2nonpkgs/rust.stuff/rust/rust/src/libstd/panic.rs:388 std::thread::Builder::spawn_unchecked::{{closure}}::hed00129e1c5572f2 at /home/xftroxgpx/build/2nonpkgs/rust.stuff/rust/rust/src/libstd/thread/mod.rs:468 >::call_box::h3d507a5e4bf27391 at /home/xftroxgpx/build/2nonpkgs/rust.stuff/rust/rust/src/liballoc/boxed.rs:734 39: std::sys_common::thread::start_thread::h7c24e4f48ce975ba (0x7ff4bcba8d06) at src/libstd/sys_common/thread.rs:14 40: std::sys::unix::thread::Thread::new::thread_start::h966b57701b78ecf1 (0x7ff4bcb9c3f5) at src/libstd/sys/unix/thread.rs:81 41: start_thread (0x7ff4b862c73e) at /usr/src/debug/glibc/nptl/pthread_create.c:486 42: __GI___clone (0x7ff4bca33bc2) 43: (0x0) real 0m7.569s user 0m1.512s sys 0m2.920s 0 / 0 thread 'main' panicked at 'wuuuuuuattttttt??!attempt to multiply with overflow', /tmp/tr/src/main.rs:12:15 stack backtrace: 0: std::sys::unix::backtrace::tracing::imp::unwind_backtrace at src/libstd/sys/unix/backtrace/tracing/gcc_s.rs:39 1: std::sys_common::backtrace::print at src/libstd/sys_common/backtrace.rs:70 at src/libstd/sys_common/backtrace.rs:58 2: std::panicking::default_hook::{{closure}} at src/libstd/panicking.rs:200 3: std::panicking::default_hook at src/libstd/panicking.rs:215 4: std::panicking::rust_panic_with_hook at src/libstd/panicking.rs:478 5: std::panicking::continue_panic_fmt at src/libstd/panicking.rs:385 6: rust_begin_unwind at src/libstd/panicking.rs:312 7: core::panicking::panic_fmt at src/libcore/panicking.rs:85 8: core::panicking::panic at src/libcore/panicking.rs:49 9: main::main at ./src/main.rs:12 10: std::rt::lang_start::{{closure}} at /home/xftroxgpx/build/2nonpkgs/rust.stuff/rust/rust/src/libstd/rt.rs:64 11: std::panicking::try::do_call at src/libstd/rt.rs:49 at src/libstd/panicking.rs:297 12: __rust_maybe_catch_panic at src/libpanic_unwind/lib.rs:92 13: std::panicking::try at src/libstd/panicking.rs:276 14: std::panic::catch_unwind at src/libstd/panic.rs:388 15: std::rt::lang_start_internal at src/libstd/rt.rs:48 16: std::rt::lang_start at /home/xftroxgpx/build/2nonpkgs/rust.stuff/rust/rust/src/libstd/rt.rs:64 17: main 18: __libc_start_main at ../csu/libc-start.c:308 19: _start at ../sysdeps/x86_64/start.S:120 ```

[dtolnay]

I agree that this would be desirable. Would love to see a PR with an implementation!

[ghost]

I found the code that codegens the panic into the executable: https://github.com/rust-lang/rust/blob/ceb2512144d1fc26330e85fb9d41c22ba1866259/src/librustc_codegen_ssa/mir/block.rs#L354-L396

and this very line(from the above): https://github.com/rust-lang/rust/blob/ceb2512144d1fc26330e85fb9d41c22ba1866259/src/librustc_codegen_ssa/mir/block.rs#L396 is the one that gets the value of the error message string attempt to multiply with overflow which can be seen at: https://github.com/rust-lang/rust/blob/ceb2512144d1fc26330e85fb9d41c22ba1866259/src/librustc/mir/interpret/error.rs#L416 and is part of the panic message that happens at runtime.

So if I'm interpreting this correctly: https://github.com/rust-lang/rust/blob/ceb2512144d1fc26330e85fb9d41c22ba1866259/src/librustc_codegen_ssa/mir/block.rs#L331 then the condition whether or not it overflowed is already a bool(or possibly something else?) there, so the operands of the mul or even the mul operation itself cannot be accessed from here.

And since I basically don't understand 95% of what's going on or what most code does here, and I'm still only at chapter 10(is next) in my rustbook reading(altho many months ago I once I went as far as(but not including) that chapter on how to build your own grep tool - oh it's chapter 12), I'm going to conclude that it's basically impossible(if at least, for me) to show the lhs,op and rhs in the panic message, simply because they aren't accessible from the context where the if cond then panic block is being codegenned into the executable. (I've only some vague understanding of this, based mostly on deductions - could someone please recommend a link to read about this? uuuu, I found something and this)

EDIT: Ha! I might actually be (gladly!) wrong! due to my interpretation of this comment // Don't codegen the panic block if success if known. which to me means that the mul operation is also codegen-ned(a few lines later) thus the lhs,op and rhs would be accessible maybe they're somehow inside cond (whatever type/struct(?) that is it) EDIT2: progressing here: https://gist.github.com/xftroxgpx/c34b67bb43ef3ca6fbd75971c460f541

[correabuscar]

Looks like this is already in stable rust 1.76.0 (at least), as I'm getting this output:

   Compiling playground v0.0.1 (/playground)
error: this arithmetic operation will overflow
 --> src/main.rs:7:20
  |
7 |     println!("{}", 2*innum);
  |                    ^^^^^^^ attempt to compute `2_i8 * 122_i8`, which would overflow
  |
  = note: `#[deny(arithmetic_overflow)]` on by default

error: could not compile `playground` (bin "playground") due to 1 previous error

Therefore the operands are shown, so this issue can be closed. Thanks all!