On Sun, Mar 5, 2017 at 10:12 PM, Henrique de Moraes Holschuh <h...@hmh.eng.br> wrote: > On Sun, 05 Mar 2017, Måns Rullgård wrote: >> Tomas Winkler <tom...@gmail.com> writes: >> > Sparse complains for arrays declared with variable length >> > >> > 'warning: Variable length array is used' >> > >> > Prior to c99 this was not allowed but lgcc (c99) doesn't have problem >> > with that https://gcc.gnu.org/onlinedocs/gcc/Variable-Length.html. >> > And also Linux kernel compilation with W=1 doesn't complain. >> > >> > Since sparse is used extensively would like to ask what is the correct >> > usage of arrays of variable length >> > within Linux Kernel. >> >> Variable-length arrays are a very bad idea. Don't use them, ever. >> If the size has a sane upper bound, just use that value statically. >> Otherwise, you have a stack overflow waiting to happen and should be >> using some kind of dynamic allocation instead. >> >> Furthermore, use of VLAs generally results in less efficient code. For >> instance, it forces gcc to waste a register for the frame pointer, and >> it often prevents inlining. > > Well, if we're going to forbid VLAs in the kernel, IMHO the kernel build > system should call gcc with -Werror=vla to get that point across early, > and flush out any offenders.
First we'd have to fix all existing offenders which are a few... -- Thanks, //richard
