From be6bb56ee0c88353a01675c4cc525020f1d3137a Mon Sep 17 00:00:00 2001 From: Ralf Jung Date: Sun, 7 Aug 2022 08:30:03 -0400 Subject: [PATCH] add -Zextra-const-ub-checks to enable more UB checking in const-eval --- .../src/const_eval/machine.rs | 10 +++ .../src/interpret/validity.rs | 4 ++ compiler/rustc_session/src/options.rs | 2 + src/test/rustdoc-ui/z-help.stdout | 1 + .../consts/extra-const-ub/detect-extra-ub.rs | 43 +++++++++++ .../extra-const-ub/detect-extra-ub.stderr | 71 +++++++++++++++++++ 6 files changed, 131 insertions(+) create mode 100644 src/test/ui/consts/extra-const-ub/detect-extra-ub.rs create mode 100644 src/test/ui/consts/extra-const-ub/detect-extra-ub.stderr diff --git a/compiler/rustc_const_eval/src/const_eval/machine.rs b/compiler/rustc_const_eval/src/const_eval/machine.rs index fc2e6652a3d72..684877cae7677 100644 --- a/compiler/rustc_const_eval/src/const_eval/machine.rs +++ b/compiler/rustc_const_eval/src/const_eval/machine.rs @@ -236,6 +236,16 @@ impl<'mir, 'tcx> interpret::Machine<'mir, 'tcx> for CompileTimeInterpreter<'mir, const PANIC_ON_ALLOC_FAIL: bool = false; // will be raised as a proper error + #[inline(always)] + fn enforce_alignment(ecx: &InterpCx<'mir, 'tcx, Self>) -> bool { + ecx.tcx.sess.opts.unstable_opts.extra_const_ub_checks + } + + #[inline(always)] + fn enforce_validity(ecx: &InterpCx<'mir, 'tcx, Self>) -> bool { + ecx.tcx.sess.opts.unstable_opts.extra_const_ub_checks + } + fn load_mir( ecx: &InterpCx<'mir, 'tcx, Self>, instance: ty::InstanceDef<'tcx>, diff --git a/compiler/rustc_const_eval/src/interpret/validity.rs b/compiler/rustc_const_eval/src/interpret/validity.rs index 6f6717721fb5a..f1b1855c3ec74 100644 --- a/compiler/rustc_const_eval/src/interpret/validity.rs +++ b/compiler/rustc_const_eval/src/interpret/validity.rs @@ -1005,6 +1005,10 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> { /// It will error if the bits at the destination do not match the ones described by the layout. #[inline(always)] pub fn validate_operand(&self, op: &OpTy<'tcx, M::Provenance>) -> InterpResult<'tcx> { + // Note that we *could* actually be in CTFE here with `-Zextra-const-ub-checks`, but it's + // still correct to not use `ctfe_mode`: that mode is for validation of the final constant + // value, it rules out things like `UnsafeCell` in awkward places. It also can make checking + // recurse through references which, for now, we don't want here, either. self.validate_operand_internal(op, vec![], None, None) } } diff --git a/compiler/rustc_session/src/options.rs b/compiler/rustc_session/src/options.rs index 1827f1c208de7..0032dd7d113f8 100644 --- a/compiler/rustc_session/src/options.rs +++ b/compiler/rustc_session/src/options.rs @@ -1310,6 +1310,8 @@ options! { "emit the bc module with thin LTO info (default: yes)"), export_executable_symbols: bool = (false, parse_bool, [TRACKED], "export symbols from executables, as if they were dynamic libraries"), + extra_const_ub_checks: bool = (false, parse_bool, [TRACKED], + "turns on more checks to detect const UB, which can be slow (default: no)"), #[cfg_attr(not(bootstrap), rustc_lint_opt_deny_field_access("use `Session::fewer_names` instead of this field"))] fewer_names: Option = (None, parse_opt_bool, [TRACKED], "reduce memory use by retaining fewer names within compilation artifacts (LLVM-IR) \ diff --git a/src/test/rustdoc-ui/z-help.stdout b/src/test/rustdoc-ui/z-help.stdout index 6dc41231559c0..236469ce9797a 100644 --- a/src/test/rustdoc-ui/z-help.stdout +++ b/src/test/rustdoc-ui/z-help.stdout @@ -38,6 +38,7 @@ -Z emit-stack-sizes=val -- emit a section containing stack size metadata (default: no) -Z emit-thin-lto=val -- emit the bc module with thin LTO info (default: yes) -Z export-executable-symbols=val -- export symbols from executables, as if they were dynamic libraries + -Z extra-const-ub-checks=val -- turns on more checks to detect const UB, which can be slow (default: no) -Z fewer-names=val -- reduce memory use by retaining fewer names within compilation artifacts (LLVM-IR) (default: no) -Z force-unstable-if-unmarked=val -- force all crates to be `rustc_private` unstable (default: no) -Z fuel=val -- set the optimization fuel quota for a crate diff --git a/src/test/ui/consts/extra-const-ub/detect-extra-ub.rs b/src/test/ui/consts/extra-const-ub/detect-extra-ub.rs new file mode 100644 index 0000000000000..ebbe315b8f818 --- /dev/null +++ b/src/test/ui/consts/extra-const-ub/detect-extra-ub.rs @@ -0,0 +1,43 @@ +// compile-flags: -Zextra-const-ub-checks +#![feature(const_ptr_read)] + +use std::mem::transmute; + +const INVALID_BOOL: () = unsafe { + let _x: bool = transmute(3u8); + //~^ ERROR: evaluation of constant value failed + //~| invalid value +}; + +const INVALID_PTR_IN_INT: () = unsafe { + let _x: usize = transmute(&3u8); + //~^ ERROR: evaluation of constant value failed + //~| invalid value +}; + +const INVALID_SLICE_TO_USIZE_TRANSMUTE: () = unsafe { + let x: &[u8] = &[0; 32]; + let _x: (usize, usize) = transmute(x); + //~^ ERROR: evaluation of constant value failed + //~| invalid value +}; + +const UNALIGNED_PTR: () = unsafe { + let _x: &u32 = transmute(&[0u8; 4]); + //~^ ERROR: evaluation of constant value failed + //~| invalid value +}; + +const UNALIGNED_READ: () = { + INNER; //~ERROR any use of this value will cause an error + //~| previously accepted + // There is an error here but its span is in the standard library so we cannot match it... + // so we have this in a *nested* const, such that the *outer* const fails to use it. + const INNER: () = unsafe { + let x = &[0u8; 4]; + let ptr = x.as_ptr().cast::(); + ptr.read(); + }; +}; + +fn main() {} diff --git a/src/test/ui/consts/extra-const-ub/detect-extra-ub.stderr b/src/test/ui/consts/extra-const-ub/detect-extra-ub.stderr new file mode 100644 index 0000000000000..66634f3dd5695 --- /dev/null +++ b/src/test/ui/consts/extra-const-ub/detect-extra-ub.stderr @@ -0,0 +1,71 @@ +error[E0080]: evaluation of constant value failed + --> $DIR/detect-extra-ub.rs:7:20 + | +LL | let _x: bool = transmute(3u8); + | ^^^^^^^^^^^^^^ constructing invalid value: encountered 0x03, but expected a boolean + +error[E0080]: evaluation of constant value failed + --> $DIR/detect-extra-ub.rs:13:21 + | +LL | let _x: usize = transmute(&3u8); + | ^^^^^^^^^^^^^^^ constructing invalid value: encountered (potentially part of) a pointer, but expected plain (non-pointer) bytes + +error[E0080]: evaluation of constant value failed + --> $DIR/detect-extra-ub.rs:20:30 + | +LL | let _x: (usize, usize) = transmute(x); + | ^^^^^^^^^^^^ constructing invalid value at .0: encountered (potentially part of) a pointer, but expected plain (non-pointer) bytes + +error[E0080]: evaluation of constant value failed + --> $DIR/detect-extra-ub.rs:26:20 + | +LL | let _x: &u32 = transmute(&[0u8; 4]); + | ^^^^^^^^^^^^^^^^^^^^ constructing invalid value: encountered an unaligned reference (required 4 byte alignment but found 1) + +error[E0080]: evaluation of constant value failed + --> $SRC_DIR/core/src/ptr/mod.rs:LL:COL + | +LL | copy_nonoverlapping(src, tmp.as_mut_ptr(), 1); + | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + | | + | accessing memory with alignment 1, but alignment 4 is required + | inside `std::ptr::read::` at $SRC_DIR/core/src/ptr/mod.rs:LL:COL + | + ::: $SRC_DIR/core/src/ptr/const_ptr.rs:LL:COL + | +LL | unsafe { read(self) } + | ---------- inside `ptr::const_ptr::::read` at $SRC_DIR/core/src/ptr/const_ptr.rs:LL:COL + | + ::: $DIR/detect-extra-ub.rs:39:9 + | +LL | ptr.read(); + | ---------- inside `INNER` at $DIR/detect-extra-ub.rs:39:9 + +error: any use of this value will cause an error + --> $DIR/detect-extra-ub.rs:32:5 + | +LL | const UNALIGNED_READ: () = { + | ------------------------ +LL | INNER; + | ^^^^^ referenced constant has errors + | + = note: `#[deny(const_err)]` on by default + = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release! + = note: for more information, see issue #71800 + +error: aborting due to 6 previous errors + +For more information about this error, try `rustc --explain E0080`. +Future incompatibility report: Future breakage diagnostic: +error: any use of this value will cause an error + --> $DIR/detect-extra-ub.rs:32:5 + | +LL | const UNALIGNED_READ: () = { + | ------------------------ +LL | INNER; + | ^^^^^ referenced constant has errors + | + = note: `#[deny(const_err)]` on by default + = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release! + = note: for more information, see issue #71800 +