Re: [PATCH] tools/libxl: remove usage of VLA arrays

[Jan Beulich <jbeulich@xxxxxxxx>]

On 28.10.2024 13:03, Andrew Cooper wrote:
> On 28/10/2024 11:48 am, Roger Pau Monne wrote:
>> Clang 19 complains with the following error when building libxl:
>>
>> libxl_utils.c:48:15: error: variable length array folded to constant array 
>> as an extension [-Werror,-Wgnu-folding-constant]
>>    48 |     char path[strlen("/local/domain") + 12];
>>       |               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>
>> Replace the usage of strlen() with ARRAY_SIZE(), which allows the literal
>> string length to be known at build time.  Note ARRAY_SIZE() accounts for the
>> NUL terminator while strlen() didn't, hence subtract 1 from the total size
>> calculation.
>>
>> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
>> ---
>>  tools/libs/light/libxl_utils.c | 4 ++--
>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/tools/libs/light/libxl_utils.c b/tools/libs/light/libxl_utils.c
>> index 10398a6c8611..b3f5e751cc3f 100644
>> --- a/tools/libs/light/libxl_utils.c
>> +++ b/tools/libs/light/libxl_utils.c
>> @@ -45,7 +45,7 @@ unsigned long libxl_get_required_shadow_memory(unsigned 
>> long maxmem_kb, unsigned
>>  char *libxl_domid_to_name(libxl_ctx *ctx, uint32_t domid)
>>  {
>>      unsigned int len;
>> -    char path[strlen("/local/domain") + 12];
>> +    char path[ARRAY_SIZE("/local/domain") + 11];
>>      char *s;
>>  
>>      snprintf(path, sizeof(path), "/local/domain/%d/name", domid);
>> @@ -141,7 +141,7 @@ int libxl_cpupool_qualifier_to_cpupoolid(libxl_ctx *ctx, 
>> const char *p,
>>  char *libxl_cpupoolid_to_name(libxl_ctx *ctx, uint32_t poolid)
>>  {
>>      unsigned int len;
>> -    char path[strlen("/local/pool") + 12];
>> +    char path[ARRAY_SIZE("/local/pool") + 11];
>>      char *s;
>>  
>>      snprintf(path, sizeof(path), "/local/pool/%d/name", poolid);
> 
> Acked-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> 
> Although I have a minor preference for sizeof() as suggested by Frediano.
> 
> Can fix on commit, if you're happy?

Please can we stick to ARRAY_SIZE() when it comes to strings? It's the
same as sizeof() when the base type is char, but the difference becomes
relevant if the base type was e.g. wchar_t.

Jan