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

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Date:   Wed, 20 Apr 2022 11:49:09 -0700 (PDT)
From:   Palmer Dabbelt <palmer@...osinc.com>
To:     rdunlap@...radead.org
CC:     panqinglin2020@...as.ac.cn,
        Paul Walmsley <paul.walmsley@...ive.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,
        lkp@...el.com
Subject:     Re: [PATCH v1] RISC-V: Add braces around an empty if statement bodies

On Tue, 19 Apr 2022 13:38:42 PDT (-0700), rdunlap@...radead.org wrote:
> 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.

Ya, that's the right way to do it -- not sure why I was being lazy here.  
Turns out there was a bunch of other XIP breakage, I sent a v2 that's a 
whole series.

Thanks!

>
>> ---
>>  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,