linux-kernel - Re: [PATCH v1] RISC-V: Add braces around an empty if statement bodies

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Date:   Tue, 19 Apr 2022 13:38:42 -0700
From:   Randy Dunlap <rdunlap@...radead.org>
To:     Palmer Dabbelt <palmer@...osinc.com>, panqinglin2020@...as.ac.cn
Cc:     Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>, aou@...s.berkeley.edu,
        alexandre.ghiti@...onical.com, jszhang@...nel.org,
        wangkefeng.wang@...wei.com, mick@....forth.gr,
        vitaly.wool@...sulko.com, rppt@...nel.org,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        kernel test robot <lkp@...el.com>
Subject: Re: [PATCH v1] RISC-V: Add braces around an empty if statement bodies

Hi,

On 4/19/22 12:48, Palmer Dabbelt wrote:
> From: Palmer Dabbelt <palmer@...osinc.com>
> 
> This triggers -Wempty-body, which will cause the next statement (eventually
> create_pmd_mapping) to be dropped.  Both of these were introduced by the same
> commit.  This is safe for the reporting config (which is 32-bit), but IIUC
> could result in breakages for 64-bit configs without 4/5 level paging like the
> XIP configs.
> 
> Reported-by: kernel test robot <lkp@...el.com>
> Fixes: 677b9eb8810e ("riscv: mm: Prepare pt_ops helper functions for sv57")
> Signed-off-by: Palmer Dabbelt <palmer@...osinc.com>
> ---
> Might be better to define these to functions that are empty, but that's
> slightly different than just fixing the commit/warning in question.

Yes, we usually fix this type of problem by changing these to have empty bodies:

#else
...
#define create_pud_mapping(__pmdp, __va, __pa, __sz, __prot)
#define create_pmd_mapping(__pmdp, __va, __pa, __sz, __prot)
#endif /* __PAGETABLE_PMD_FOLDED */

etc.

> ---
>  arch/riscv/mm/init.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
> index 9535bea8688c..637916857c4d 100644
> --- a/arch/riscv/mm/init.c
> +++ b/arch/riscv/mm/init.c
> @@ -798,13 +798,15 @@ static void __init create_fdt_early_page_table(pgd_t *pgdir, uintptr_t dtb_pa)
>  			   PGDIR_SIZE,
>  			   IS_ENABLED(CONFIG_64BIT) ? PAGE_TABLE : PAGE_KERNEL);
>  
> -	if (pgtable_l5_enabled)
> +	if (pgtable_l5_enabled) {
>  		create_p4d_mapping(early_dtb_p4d, DTB_EARLY_BASE_VA,
>  				   (uintptr_t)early_dtb_pud, P4D_SIZE, PAGE_TABLE);
> +	}
>  
> -	if (pgtable_l4_enabled)
> +	if (pgtable_l4_enabled) {
>  		create_pud_mapping(early_dtb_pud, DTB_EARLY_BASE_VA,
>  				   (uintptr_t)early_dtb_pmd, PUD_SIZE, PAGE_TABLE);
> +	}
>  
>  	if (IS_ENABLED(CONFIG_64BIT)) {
>  		create_pmd_mapping(early_dtb_pmd, DTB_EARLY_BASE_VA,

-- 
~Randy