# \`check-bounds=no\` causes illegal memory access when using \`rand()\` in CUDA kernel

**URL:** <https://discourse.julialang.org/t/check-bounds-no-causes-illegal-memory-access-when-using-rand-in-cuda-kernel/129455>\
**Category:** GPU\
**Tags:** question, bug, error, random\
**Created:** [May 30, 2025, 2:41am UTC](https://discourse.julialang.org/t/check-bounds-no-causes-illegal-memory-access-when-using-rand-in-cuda-kernel/129455 "2025-05-30T02:41:23Z")\
**Posts on this page:** 4\
**Page:** 1

<div class="post-metadata">

**Author:** ![0samuraiE](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/0samuraie/32/209825_2.png) [@0samuraiE](https://discourse.julialang.org/u/0samuraiE)\
**Post date:** [May 30, 2025, 2:41am UTC](https://discourse.julialang.org/t/check-bounds-no-causes-illegal-memory-access-when-using-rand-in-cuda-kernel/129455/1 "2025-05-30T02:41:23Z")

</div>

I’m encountering an error when running the following minimal example with `check-bounds=no`. With bounds checking enabled (`check-bounds=yes`), it works fine. But disabling it causes:

```julia
ERROR: CUDA error: an illegal memory access was encountered (code 700, ERROR_ILLEGAL_ADDRESS)

```

Here is the MWE:

```julia
using CUDA

function test(A)
    A[1] = rand()
    return nothing
end

A = CUDA.zeros(1)
CUDA.@sync @cuda test(A)

```

Is this error caused by using rand() inside the kernel?  
Is it fundamentally incorrect to use rand() inside a @cuda kernel?  
If so, what is the proper way to generate random numbers on the GPU?  
Any clarification would be appreciated.

versioninfo

```julia
Julia Version 1.11.5
Commit 760b2e5b739 (2025-04-14 06:53 UTC)
Build Info:
  Official https://julialang.org/ release
Platform Info:
  OS: Linux (x86_64-linux-gnu)
  CPU: 384 × AMD EPYC 9654 96-Core Processor
  WORD_SIZE: 64
  LLVM: libLLVM-16.0.6 (ORCJIT, znver4)
Threads: 1 default, 0 interactive, 1 GC (on 384 virtual cores)
Environment:
  LD_LIBRARY_PATH = /apps/t4/rhel9/free/cudnn/9.8.0/cuda/12/lib:/apps/t4/rhel9/free/hdf5-parallel/1.14.3/nvhpc24.1/openmpi5.0.2/lib:/apps/t4/rhel9/free/openmpi/5.0.2/nvhpc/lib:/apps/t4/rhel9/free/ucx/1.16.0-gcc/lib:/apps/t4/rhel9/isv/nvidia/hpc_sdk/Linux_x86_64/25.1/comm_libs/nvshmem/lib:/apps/t4/rhel9/isv/nvidia/hpc_sdk/Linux_x86_64/25.1/comm_libs/nccl/lib:/apps/t4/rhel9/isv/nvidia/hpc_sdk/Linux_x86_64/25.1/math_libs/lib64:/apps/t4/rhel9/isv/nvidia/hpc_sdk/Linux_x86_64/25.1/compilers/lib:/apps/t4/rhel9/isv/nvidia/hpc_sdk/Linux_x86_64/25.1/compilers/extras/qd/lib:/apps/t4/rhel9/isv/nvidia/hpc_sdk/Linux_x86_64/25.1/cuda/lib64
  JULIA_DEPOT_PATH = /gs/fs/private/.julia

```

CUDA.versioninfo()

```julia
CUDA runtime 12.6, local installation
CUDA driver 12.9
NVIDIA driver 570.124.6

CUDA libraries:
- CUBLAS: 12.6.4
- CURAND: 10.3.7
- CUFFT: 11.3.0
- CUSOLVER: 11.7.1
- CUSPARSE: 12.5.4
- CUPTI: 2024.3.2 (API 24.0.0)
- NVML: 12.0.0+570.124.6

Julia packages:
- CUDA: 5.8.2
- CUDA_Driver_jll: 0.13.0+0
- CUDA_Runtime_jll: 0.17.0+0
- CUDA_Runtime_Discovery: 0.3.5

Toolchain:
- Julia: 1.11.5
- LLVM: 16.0.6

Preferences:
- CUDA_Runtime_jll.version: 12.6
- CUDA_Runtime_jll.local: true

1 device:
  0: NVIDIA H100 (sm_90, 92.489 GiB / 93.584 GiB available)

```

---

<div class="post-metadata">

**Author:** ![0samuraiE](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/0samuraie/32/209825_2.png) [@0samuraiE](https://discourse.julialang.org/u/0samuraiE)\
**Post date:** [May 30, 2025, 3:07am UTC](https://discourse.julialang.org/t/check-bounds-no-causes-illegal-memory-access-when-using-rand-in-cuda-kernel/129455/2 "2025-05-30T03:07:48Z")

</div>

This MWE also crashed when `check-bounds=no`

```julia
using CUDA
N = 10^5
A = CUDA.rand(N)
B = CUDA.zeros(Int, N)
sortperm!(B, A)

```

```julia
100000-element CuArray{Int64, 1, CUDA.DeviceMemory}:
Error showing value of type CuArray{Int64, 1, CUDA.DeviceMemory}:

SYSTEM (REPL): showing an error caused an error
ERROR: CUDA error: an illegal memory access was encountered (code 700, ERROR_ILLEGAL_ADDRESS)

```

---

<div class="post-metadata">

**Author:** ![0samuraiE](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/0samuraie/32/209825_2.png) [@0samuraiE](https://discourse.julialang.org/u/0samuraiE)\
**Post date:** [May 31, 2025, 5:39am UTC](https://discourse.julialang.org/t/check-bounds-no-causes-illegal-memory-access-when-using-rand-in-cuda-kernel/129455/3 "2025-05-31T05:39:43Z")

</div>

Additional information:  
These MWEs work properly in CUDA 5.7, but not in CUDA 5.8 — this appears to be a regression.

---

<div class="post-metadata">

**Author:** ![maleadt](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/maleadt/32/10097_2.png) [@maleadt](https://discourse.julialang.org/u/maleadt)\
**Post date:** [May 31, 2025, 7:38am UTC](https://discourse.julialang.org/t/check-bounds-no-causes-illegal-memory-access-when-using-rand-in-cuda-kernel/129455/4 "2025-05-31T07:38:44Z")

</div>

> [@0samuraiE](#):
>
> ```julia
> using CUDA
> N = 10^5
> A = CUDA.rand(N)
> B = CUDA.zeros(Int, N)
> sortperm!(B, A)
> 
> ```

Thanks for the MWE. I bisected and filed an issue: [Illegal memory access after aligned\_sizeof changes · Issue #2790 · JuliaGPU/CUDA.jl · GitHub](https://github.com/JuliaGPU/CUDA.jl/issues/2790)

The issue is caused by CUDA.jl switching from `sizeof` to `aligned_sizeof`. If you want to help: It should be relatively easy to figure out which exact change caused the issue, and how that affects `sortperm!` here (since `sizeof` and `aligned_sizeof` of the `Float32` eltype used here shouldn’t have any impact).