On 02/06/2015 11:23 AM, Kees Cook wrote: > > Strictly speaking (ISO C, "man 3 errno"), errno is supposed to be a > full int, though digging around I find this in include/linux/err.h: > That doesn't mean the kernel has to support them. > /* > * Kernel pointers have redundant information, so we can use a > * scheme where we can return either an error code or a normal > * pointer with the same return value. > * > * This should be a per-architecture thing, to allow different > * error and pointer decisions. > */ > #define MAX_ERRNO 4095 > > #ifndef __ASSEMBLY__ > > #define IS_ERR_VALUE(x) unlikely((x) >= (unsigned long)-MAX_ERRNO) > > But no architecture overrides this. > We used to have a much lower value, that was per-architecture, in order to optimize the resulting assembly (e.g. 8-bit immediates on x86). This didn't work as the number of errnos increased. The other motivation was probably binary compatibility with other Unices, which was an idea for a while. -hpa
