From: Mathieu Desnoyers > Sent: 12 January 2022 15:06 > > ----- On Jan 12, 2022, at 9:58 AM, David Laight David.Laight@xxxxxxxxxx wrote: > > >> * [*] The openrisc, powerpc64 and x86-64 architectures define a "redzone" as a > >> * stack area beyond the stack pointer which can be used by the compiler > >> * to store local variables in leaf functions. > > > > I wonder if that is really worth the trouble it causes! > > By the time a function is spilling values to stack the cost > > of a %sp update is almost certainly noise. > > > > Someone clearly thought it was a 'good idea (tm)'. > > I must admit that I've been surprised to learn about these redzones. Thanks for > pointing them out to me, it was clearly a blind spot. I suspect it would be useful > to introduce per-architecture KERNEL_REDZONE, USER_REDZONE and COMPAT_USER_REDZONE > with a asm-generic version defining them to 0, with proper documentation. It would > make it clearer to kernel developers working on stuff similar to signal handler > delivery that they need to consider these carefully. They can never be used in kernel - any ISR would overwrite them. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
