made `unreachable_unchecked` panic in debug mode #100021

cbrownsey · 2022-08-01T11:52:35Z

Added a call to unreachable when unreachable_unchecked is compiled with debug_assertions enabled. I don't know if this is an issue, but this shouldn't cause any problems with const fns, as panicking in const fns was added in the release that this was made const.

rustbot · 2022-08-01T11:52:38Z

Hey! It looks like you've submitted a new PR for the library teams!

If this PR contains changes to any rust-lang/rust public library APIs then please comment with @rustbot label +T-libs-api -T-libs to tag it appropriately. If this PR contains changes to any unstable APIs please edit the PR description to add a link to the relevant API Change Proposal or create one if you haven't already. If you're unsure where your change falls no worries, just leave it as is and the reviewer will take a look and make a decision to forward on if necessary.

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rust-highfive · 2022-08-01T11:52:38Z

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @joshtriplett (or someone else) soon.

Please see the contribution instructions for more information.

rust-log-analyzer · 2022-08-01T12:15:57Z

The job x86_64-gnu-llvm-12 failed! Check out the build log: (web) (plain)

Click to see the possible cause of the failure (guessed by this bot)

- LL |     unsafe { intrinsics::unreachable() }
-    |              ^^^^^^^^^^^^^^^^^^^^^^^^^
-    |              |
-    |              entering unreachable code
-    |              inside `unreachable_unchecked` at $SRC_DIR/core/src/hint.rs:LL:COL
+ LL |         unreachable!()
+    |         |
+    |         the evaluated program panicked at 'internal error: entered unreachable code', $SRC_DIR/core/src/hint.rs:LL:COL
+    |         the evaluated program panicked at 'internal error: entered unreachable code', $SRC_DIR/core/src/hint.rs:LL:COL
+    |         inside `unreachable_unchecked` at $SRC_DIR/core/src/panic.rs:LL:COL
10   ::: $DIR/const_unsafe_unreachable_ub.rs:6:18
11    |

14 ...
14 ...
15 LL | const BAR: bool = unsafe { foo(false) };
16    |                            ---------- inside `BAR` at $DIR/const_unsafe_unreachable_ub.rs:10:28
+    |
+    = note: this error originates in the macro `$crate::panic::unreachable_2021` which comes from the expansion of the macro `unreachable` (in Nightly builds, run with -Z macro-backtrace for more info)
Some tests failed in compiletest suite=ui mode=ui host=x86_64-unknown-linux-gnu target=x86_64-unknown-linux-gnu
18 error: aborting due to previous error
19 



The actual stderr differed from the expected stderr.
Actual stderr saved to /checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/consts/const_unsafe_unreachable_ub/const_unsafe_unreachable_ub.stderr
To only update this specific test, also pass `--test-args consts/const_unsafe_unreachable_ub.rs`

error: 1 errors occurred comparing output.
status: exit status: 1
status: exit status: 1
command: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/bin/rustc" "/checkout/src/test/ui/consts/const_unsafe_unreachable_ub.rs" "-Zthreads=1" "--target=x86_64-unknown-linux-gnu" "--error-format" "json" "--json" "future-incompat" "-Ccodegen-units=1" "-Zui-testing" "-Zdeduplicate-diagnostics=no" "-Cstrip=debuginfo" "--emit" "metadata" "-C" "prefer-dynamic" "--out-dir" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/consts/const_unsafe_unreachable_ub" "-A" "unused" "-Crpath" "-Cdebuginfo=0" "-Lnative=/checkout/obj/build/x86_64-unknown-linux-gnu/native/rust-test-helpers" "-L" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/consts/const_unsafe_unreachable_ub/auxiliary"
stdout: none
--- stderr -------------------------------
  --> /checkout/library/core/src/hint.rs:102:9
   |
LL |         unreachable!()
   |         ^^^^^^^^^^^^^^
---
   |
LL |         false => std::hint::unreachable_unchecked(),
   |                  ---------------------------------- inside `foo` at /checkout/src/test/ui/consts/const_unsafe_unreachable_ub.rs:6:18
...
LL | const BAR: bool = unsafe { foo(false) };
   |                            ---------- inside `BAR` at /checkout/src/test/ui/consts/const_unsafe_unreachable_ub.rs:10:28
   |
   = note: this error originates in the macro `$crate::panic::unreachable_2021` which comes from the expansion of the macro `unreachable` (in Nightly builds, run with -Z macro-backtrace for more info)
error: aborting due to previous error

For more information about this error, try `rustc --explain E0080`.
------------------------------------------
------------------------------------------


---- [ui] src/test/ui/extern/issue-64655-extern-rust-must-allow-unwind.rs#fat0 stdout ----

error in revision `fat0`: test compilation failed although it shouldn't!
status: exit status: 1
command: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/bin/rustc" "/checkout/src/test/ui/extern/issue-64655-extern-rust-must-allow-unwind.rs" "-Zthreads=1" "--target=x86_64-unknown-linux-gnu" "--cfg" "fat0" "--error-format" "json" "--json" "future-incompat" "-Ccodegen-units=1" "-Zui-testing" "-Zdeduplicate-diagnostics=no" "-Cstrip=debuginfo" "-o" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/extern/issue-64655-extern-rust-must-allow-unwind.fat0/a" "-Crpath" "-Cdebuginfo=0" "-Lnative=/checkout/obj/build/x86_64-unknown-linux-gnu/native/rust-test-helpers" "-C" "opt-level=0" "-C" "lto=fat" "-L" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/extern/issue-64655-extern-rust-must-allow-unwind.fat0/auxiliary"
stdout: none
--- stderr -------------------------------
error: linking with `cc` failed: exit status: 1
   |
   = note: "cc" "-m64" "/tmp/rustcJLHty1/symbols.o" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/extern/issue-64655-extern-rust-must-allow-unwind.fat0/a.issue_64655_extern_rust_must_allow_unwind.2a84b153-cgu.0.rcgu.o" "-Wl,--as-needed" "-L" "/checkout/obj/build/x86_64-unknown-linux-gnu/native/rust-test-helpers" "-L" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/extern/issue-64655-extern-rust-must-allow-unwind.fat0/auxiliary" "-L" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/lib/rustlib/x86_64-unknown-linux-gnu/lib" "-Wl,--start-group" "-Wl,--end-group" "-Wl,-Bstatic" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/lib/rustlib/x86_64-unknown-linux-gnu/lib/libcompiler_builtins-07150088dcceb2ba.rlib" "-Wl,-Bdynamic" "-lgcc_s" "-lutil" "-lrt" "-lpthread" "-lm" "-ldl" "-lc" "-Wl,--eh-frame-hdr" "-Wl,-znoexecstack" "-L" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/lib/rustlib/x86_64-unknown-linux-gnu/lib" "-o" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/extern/issue-64655-extern-rust-must-allow-unwind.fat0/a" "-Wl,--gc-sections" "-pie" "-Wl,-zrelro,-znow" "-Wl,--strip-debug" "-nodefaultlibs" "-Wl,-rpath,$ORIGIN/../../../../stage2/lib/rustlib/x86_64-unknown-linux-gnu/lib" "-Wl,--enable-new-dtags" "-Wl,-z,origin"
   = note: /usr/bin/ld: /checkout/obj/build/x86_64-unknown-linux-gnu/stage2/lib/rustlib/x86_64-unknown-linux-gnu/lib/libcompiler_builtins-07150088dcceb2ba.rlib(compiler_builtins-07150088dcceb2ba.compiler_builtins.ea377314-cgu.117.rcgu.o): in function `compiler_builtins::int::specialized_div_rem::zero_div_fn':
           compiler_builtins.ea377314-cgu.117:(.text._ZN17compiler_builtins3int19specialized_div_rem11zero_div_fn17hf34ec29fbbf93557E+0x16): undefined reference to `core::panicking::panic'
           collect2: error: ld returned 1 exit status
           
   = help: some `extern` functions couldn't be found; some native libraries may need to be installed or have their path specified
   = note: use the `-l` flag to specify native libraries to link
   = note: use the `cargo:rustc-link-lib` directive to specify the native libraries to link with Cargo (see https://doc.rust-lang.org/cargo/reference/build-scripts.html#cargorustc-link-libkindname)
error: aborting due to previous error
------------------------------------------



---- [ui] src/test/ui/issues/issue-44056.rs stdout ----

error: test compilation failed although it shouldn't!
status: exit status: 1
command: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/bin/rustc" "/checkout/src/test/ui/issues/issue-44056.rs" "-Zthreads=1" "--target=x86_64-unknown-linux-gnu" "--error-format" "json" "--json" "future-incompat" "-Ccodegen-units=1" "-Zui-testing" "-Zdeduplicate-diagnostics=no" "-Cstrip=debuginfo" "--out-dir" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/issues/issue-44056" "-A" "unused" "-Crpath" "-Cdebuginfo=0" "-Lnative=/checkout/obj/build/x86_64-unknown-linux-gnu/native/rust-test-helpers" "-Ctarget-feature=+avx" "-Clto" "-L" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/issues/issue-44056/auxiliary"
stdout: none
--- stderr -------------------------------
error: linking with `cc` failed: exit status: 1
   |
   = note: "cc" "-m64" "/tmp/rustcyXhZ3b/symbols.o" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/issues/issue-44056/issue-44056.issue_44056.9f62d9c4-cgu.0.rcgu.o" "-Wl,--as-needed" "-L" "/checkout/obj/build/x86_64-unknown-linux-gnu/native/rust-test-helpers" "-L" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/issues/issue-44056/auxiliary" "-L" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/lib/rustlib/x86_64-unknown-linux-gnu/lib" "-Wl,--start-group" "-Wl,--end-group" "-Wl,-Bstatic" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/lib/rustlib/x86_64-unknown-linux-gnu/lib/libcompiler_builtins-07150088dcceb2ba.rlib" "-Wl,-Bdynamic" "-lgcc_s" "-lutil" "-lrt" "-lpthread" "-lm" "-ldl" "-lc" "-Wl,--eh-frame-hdr" "-Wl,-znoexecstack" "-L" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/lib/rustlib/x86_64-unknown-linux-gnu/lib" "-o" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/issues/issue-44056/issue-44056" "-Wl,--gc-sections" "-pie" "-Wl,-zrelro,-znow" "-Wl,--strip-debug" "-nodefaultlibs" "-Wl,-rpath,$ORIGIN/../../../../stage2/lib/rustlib/x86_64-unknown-linux-gnu/lib" "-Wl,--enable-new-dtags" "-Wl,-z,origin"
   = note: /usr/bin/ld: /checkout/obj/build/x86_64-unknown-linux-gnu/stage2/lib/rustlib/x86_64-unknown-linux-gnu/lib/libcompiler_builtins-07150088dcceb2ba.rlib(compiler_builtins-07150088dcceb2ba.compiler_builtins.ea377314-cgu.117.rcgu.o): in function `compiler_builtins::int::specialized_div_rem::zero_div_fn':
           compiler_builtins.ea377314-cgu.117:(.text._ZN17compiler_builtins3int19specialized_div_rem11zero_div_fn17hf34ec29fbbf93557E+0x16): undefined reference to `core::panicking::panic'
           collect2: error: ld returned 1 exit status
           
   = help: some `extern` functions couldn't be found; some native libraries may need to be installed or have their path specified
   = note: use the `-l` flag to specify native libraries to link
   = note: use the `cargo:rustc-link-lib` directive to specify the native libraries to link with Cargo (see https://doc.rust-lang.org/cargo/reference/build-scripts.html#cargorustc-link-libkindname)
error: aborting due to previous error
------------------------------------------

klensy · 2022-08-02T14:08:16Z

cfg!(debug_assertions) will generate runtime check (or not?) (https://doc.rust-lang.org/rust-by-example/attribute/cfg.html), making unreachable_unchecked useless for purposes of using it for some optimizations?

i.e. if unreachable_unchecked used to eliminate some execution branch, now it will not be eliminated, as there will be runtime check for debug_assertions.

Played with it a little, looks like i'm wrong.

joshtriplett · 2022-10-03T12:53:13Z

I think this behavior change would need discussion and an FCP.

Nominating for a meeting.

m-ou-se · 2022-10-04T15:10:01Z

We briefly discussed this in the libs-api meeting. We're in favor of this change, but we'd like to make sure this doesn't result in an unwinding panic, since that will most likely not be helpful, and might make things worse.

library/core/src/hint.rs

bors · 2022-10-08T21:55:28Z

☔ The latest upstream changes (presumably #102315) made this pull request unmergeable. Please resolve the merge conflicts.

scottmcm · 2022-10-11T13:57:45Z

It sounds like libs-api would rather this abort instead of panic, in the debug case.

@rustbot author
r? @scottmcm

scottmcm · 2022-10-11T13:59:52Z

library/core/src/hint.rs

-    // SAFETY: the safety contract for `intrinsics::unreachable` must
-    // be upheld by the caller.
-    unsafe { intrinsics::unreachable() }
+    if cfg!(debug_assertions) {


Consider making this

Suggested change

if cfg!(debug_assertions) {

if cfg!(debug_assertions) && !cfg!(miri) {

since the comment on line 99 implies that Miri will already give good diagnostics for hitting unreachable.

pitaj · 2023-01-29T03:19:46Z

library/core/src/hint.rs

-    // SAFETY: the safety contract for `intrinsics::unreachable` must
-    // be upheld by the caller.
-    unsafe { intrinsics::unreachable() }
+    if cfg!(debug_assertions) {


Should this use assert_unsafe_precondition instead?

Dylan-DPC · 2023-02-22T18:47:34Z

@cbrownsey any updates to this pr?

Dylan-DPC · 2023-10-07T09:58:53Z

Closing this as inactive. Feel free to reöpen this pr or create a new pr if you get the time to work on this. Thanks

made unreachable_unchecked panic in debug mode

20f26d4

rustbot added the T-libs Relevant to the library team, which will review and decide on the PR/issue. label Aug 1, 2022

rust-highfive assigned joshtriplett Aug 1, 2022

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scottmcm added the T-libs-api Relevant to the library API team, which will review and decide on the PR/issue. label Aug 1, 2022

jyn514 approved these changes Aug 1, 2022

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joshtriplett added needs-fcp This change is insta-stable, or significant enough to need a team FCP to proceed. and removed T-libs Relevant to the library team, which will review and decide on the PR/issue. labels Oct 3, 2022

joshtriplett added the I-libs-api-nominated Nominated for discussion during a libs-api team meeting. label Oct 3, 2022

m-ou-se removed the I-libs-api-nominated Nominated for discussion during a libs-api team meeting. label Oct 4, 2022

scottmcm reviewed Oct 4, 2022

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rustbot removed the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Oct 11, 2022

rust-highfive assigned scottmcm and unassigned joshtriplett Oct 11, 2022

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Dylan-DPC closed this Oct 7, 2023

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Uh oh!

made `unreachable_unchecked` panic in debug mode #100021

made `unreachable_unchecked` panic in debug mode #100021

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cbrownsey commented Aug 1, 2022

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klensy commented Aug 2, 2022 •

edited

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Dylan-DPC commented Oct 7, 2023

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	if cfg!(debug_assertions) {
	if cfg!(debug_assertions) && !cfg!(miri) {

made unreachable_unchecked panic in debug mode #100021

made unreachable_unchecked panic in debug mode #100021

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made `unreachable_unchecked` panic in debug mode #100021

made `unreachable_unchecked` panic in debug mode #100021

klensy commented Aug 2, 2022 •

edited

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