Re: ISO C90 compilation error

["Philippe Mathieu-Daudé" <philmd@linaro.org>]

On 29/2/24 08:59, Daniel P. Berrangé wrote:
> On Thu, Feb 29, 2024 at 07:03:35AM +0000, Paz Offer wrote:
>> Hi,
>>
>> I am trying to build my code with QEMU and getting compilation error according to the ISO C90 standard:
>>
>>       const size_t buf_size = 31;
>>       char buffer[buf_size + 1];
>>
>>       error: ISO C90 forbids array ‘buffer’ whose size can’t be evaluated [-Werror=vla]
>>
>> I noticed that the code builds with '-std=gnu11', which is newer then
>> C90, so this is not clear to me why I get this error.
>> Where is the correct place to specify the language version for this?
> 
> QEMU has set compiler flags to explicitly /forbid/ use of variable
> sized arrays on the stack, as it is a known dangerous language
> feature. You must refactor your changes to avoid this by using either
> a statically sized array, or allocating on the heap.

If you array has a fixed size, you could use a definition, so the
proprocessor can evaluate the buffer size:

   #define BUF_SIZE 31
   char buffer[BUF_SIZE + 1];

Regards,

Phil.