Re: [PATCH] sparc: Replace one-element array with flexible array member

["Gustavo A. R. Silva" <gustavo@embeddedor.com>]

On 11/11/24 14:01, Thorsten Blum wrote:
> Replace the deprecated one-element array with a modern flexible array
> member in the struct hvtramp_descr.
> 
> Additionally, 15 unnecessary bytes are allocated for hdesc, but instead

15? unnecessary?

> of fixing the parentheses in the open-coded version, use struct_size()
> to calculate the correct number of bytes.
> 
> Link: https://github.com/KSPP/linux/issues/79
> Signed-off-by: Thorsten Blum <thorsten.blum@linux.dev>
> ---
>   arch/sparc/include/asm/hvtramp.h | 2 +-
>   arch/sparc/kernel/smp_64.c       | 4 +---
>   2 files changed, 2 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/sparc/include/asm/hvtramp.h b/arch/sparc/include/asm/hvtramp.h
> index 688ea43af0f5..ce2453ea4f2b 100644
> --- a/arch/sparc/include/asm/hvtramp.h
> +++ b/arch/sparc/include/asm/hvtramp.h
> @@ -17,7 +17,7 @@ struct hvtramp_descr {
>   	__u64			fault_info_va;
>   	__u64			fault_info_pa;
>   	__u64			thread_reg;
> -	struct hvtramp_mapping	maps[1];
> +	struct hvtramp_mapping	maps[];
>   };

It seems this struct is a candidate for `__counted_by()`

>   
>   void hv_cpu_startup(unsigned long hvdescr_pa);
> diff --git a/arch/sparc/kernel/smp_64.c b/arch/sparc/kernel/smp_64.c
> index e40c395db202..24d980220bf1 100644
> --- a/arch/sparc/kernel/smp_64.c
> +++ b/arch/sparc/kernel/smp_64.c
> @@ -297,9 +297,7 @@ static void ldom_startcpu_cpuid(unsigned int cpu, unsigned long thread_reg,
>   	unsigned long hv_err;
>   	int i;
>   
> -	hdesc = kzalloc(sizeof(*hdesc) +
> -			(sizeof(struct hvtramp_mapping) *
> -			 num_kernel_image_mappings - 1),
> +	hdesc = kzalloc(struct_size(hdesc, maps, num_kernel_image_mappings - 1),
>   			GFP_KERNEL);

Now the code is broken because it's allocating `num_kernel_image_mappings - 1`
elements instead of `num_kernel_image_mappings`.

--
Gustavo