llvm lint: buffer overflow in src/test/ui/foreign/foreign-truncated-arguments.rs

code from tests/ui/foreign/foreign-truncated-arguments.rs

// run-pass
// compile-flags: -O
// Regression test for https://github.com/rust-lang/rust/issues/33868

#[repr(C)]
pub struct S {
    a: u32,
    b: f32,
    c: u32
}

#[no_mangle]
#[inline(never)]
pub extern "C" fn test(s: S) -> u32 {
    s.c
}

fn main() {
    assert_eq!(test(S{a: 0, b: 0.0, c: 42}), 42);
}

When checked with rustc -Cpasses=lint src/test/ui/foreign/foreign-truncated-arguments.rs, this generates the following llvm-ir lint warning:

Undefined behavior: Buffer overflow
  %13 = load { i64, i32 }, { i64, i32 }* %12, align 4

repo @ 2342cc3

I captured the LLVM-IR in a single codegen unit, then ran opt -lint which has the same complaint, just on %4.

$ opt -disable-output -lint foreign-truncated-arguments.ll
Undefined behavior: Buffer overflow
  %4 = load { i64, i32 }, { i64, i32 }* %3, align 4

Here are the relevant snippets from that IR:

%S = type { [0 x i32], i32, [0 x i32], float, [0 x i32], i32, [0 x i32] }
[...]
; foreign_truncated_arguments::main
; Function Attrs: nonlazybind uwtable
define internal void @_ZN27foreign_truncated_arguments4main17h8a09fc9d120f0135E() unnamed_addr #1 {
start:
  %_26 = alloca i32*, align 8
  %_24 = alloca i32*, align 8
  %_22 = alloca { i64*, i64* }, align 8
  %_21 = alloca [2 x { i8*, i64* }], align 8
  %_14 = alloca %"core::fmt::Arguments", align 8
  %_4 = alloca %S, align 4
  %_3 = alloca i32, align 4
  %_1 = alloca { i32*, i32* }, align 8
  %0 = bitcast %S* %_4 to i32*
  store i32 0, i32* %0, align 4
  %1 = getelementptr inbounds %S, %S* %_4, i32 0, i32 3
  store float 0.000000e+00, float* %1, align 4
  %2 = getelementptr inbounds %S, %S* %_4, i32 0, i32 5
  store i32 42, i32* %2, align 4
  %3 = bitcast %S* %_4 to { i64, i32 }*
  %4 = load { i64, i32 }, { i64, i32 }* %3, align 4
  %5 = call i32 @test({ i64, i32 } %4)
  store i32 %5, i32* %_3, align 4
  br label %bb1

I expect S has size 12, but { i64, i32 } would have alignment padding up to size 16.

The lint goes away if I change all { i64, i32 } to packed <{ i64, i32 }>, but maybe we can do better than that.

We've been working on enabling ASAN in rusty_v8 (https://github.com/denoland/rusty_v8) and we suspect this is causing some real-world bugs when we call into V8 from Rust. In particular, some exceptions in V8 aren't correctly detected when we compile the Rust parts with opt-level=0.

@rustbot

WG-prioritization assigning priority (Zulip discussion).

@rustbot label -I-prioritize +P-high

@rustbot

{ i64, i32 } should have 16 bytes on x86_64.

@rustbot claim

Auto merge of rust-lang#127168 - DianQK:cast-size, r=workingjubilee

Rollup merge of rust-lang#127168 - DianQK:cast-size, r=workingjubilee

Unrolled build for rust-lang#127168

reopening to follow the beta backport of #127168

@mmastrac

We've been working on enabling ASAN in rusty_v8 (https://github.com/denoland/rusty_v8) and we suspect this is causing some real-world bugs when we call into V8 from Rust. In particular, some exceptions in V8 aren't correctly detected when we compile the Rust parts with opt-level=0.

@mmastrac Can you reproduce the problem on the latest nightly? I can't confirm that #127168 has fixed it.

@apiraino

@apiraino We can close it again.

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llvm lint: buffer overflow in src/test/ui/foreign/foreign-truncated-arguments.rs #75839

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llvm lint: buffer overflow in src/test/ui/foreign/foreign-truncated-arguments.rs #75839

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cuviper commented on Aug 24, 2020

mmastrac commented on Apr 13, 2024

apiraino commented on Apr 15, 2024

dianqk commented on Jun 30, 2024

apiraino commented on Jul 3, 2024

dianqk commented on Jul 4, 2024

dianqk commented on Jul 5, 2024

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