On Wed, Aug 09, 2017 at 02:41:59PM +0200, Arnd Bergmann wrote: > On Wed, Aug 9, 2017 at 12:57 AM, Dmitry V. Levin <ldv@xxxxxxxxxxxx> wrote: > > On Sun, Aug 06, 2017 at 06:44:05PM +0200, Mikko Rapeli wrote: > >> Arnd Bergmann <arnd@xxxxxxxx> doubts that __kernel_size_t could be used here > >> so trying to fall back to gcc's <stddef.h>. > > > > The only architecture where you cannot do this safely is x86 family > > because of x32 exception. If there is no chance that the change will > > affect x32, feel free to replace size_t with __kernel_size_t like I did > > some time ago, see > > http://lkml.kernel.org/r/20170302002022.GB27097@xxxxxxxxxxxx > > There is another problem: on some 32-bit architectures, size_t is > defined as 'unsigned int', while '__kernel_size_t' is defined as 'unsigned > long'. These obviously have the same size, but the man page > explicitly defines it as 'size_t ss_size'. > > If a user space program accesses the field in a way requires an > exact type match, it gets a warning or error, e.g. > > 1. printf("signal with %zd bytes\n", stack->ss_size); > 2. size_t *pointer_to_size_t = &stack->ss_size; > 3. assert(__builtin_types_compatible_p(size_t, typeof(stack->ss_size))) > > Not sure how important those are, but I think there is at least a risk > of any of those showing up in user space. Agreed, one has to take this issue into consideration when replacing size_t with __kernel_size_t. -- ldv
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