Re: [PATCH] dma_map_benchmark: fix incorrect array access in printf

[Shuah Khan <skhan@linuxfoundation.org>]

On 11/6/25 18:55, Zhang Chujun wrote:
> On Tue, Nov 05, 2025 at 08:30:00PM +0800, Zhang Chujun wrote:
>> The printf statement attempts to print the DMA direction string using
>> the syntax 'dir[directions]', which is an invalid array access. The
>> variable 'dir' is an integer, and 'directions' is a char pointer array.
>> This incorrect syntax should be 'directions[dir]', using 'dir' as the
>> index into the 'directions' array. Fix this by correcting the array
>> access from 'dir[directions]' to 'directions[dir]'.
> 
> Hi Shuah,
> 
> Thanks for your patience.
> 
> I found this issue while carefully reading the code in
> `dma_map_benchmark.c`. The expression `dir[directions]` stood out because
> `dir` is an integer (enum or int), while `directions` is a string array —
> so using `dir` as the index into `directions` is the correct form.
> Although C allows `a[b]` and `b[a]` syntactically due to pointer arithmetic,
> in this context `dir[directions]` is logically wrong and would print an
> unexpected (likely garbage) string, since it treats the address of the
> string array as an array indexed by a small integer.
> 
> The compiler doesn’t warn because `dir[directions]` is technically valid
> C (equivalent to `*(directions + dir)`), but semantically it’s backwards
> and breaks the intended output.
> 

Applied to linux-kselftest next for Linux 6.19-rc1

thanks,
-- Shuah