> -----Original Message----- > From: Arnd Bergmann [mailto:arnd@xxxxxxxx] > Sent: Friday, February 18, 2011 1:45 AM > To: Guan Xuetao > Cc: linux-kernel@xxxxxxxxxxxxxxx; linux-arch@xxxxxxxxxxxxxxx; 'Greg KH' > Subject: Re: [PATCH 05/12] unicore32 additional architecture files: low-level lib: uaccess > > On Wednesday 16 February 2011, Guan Xuetao wrote: > > + > > +#define __kernel_ok (segment_eq(get_fs(), KERNEL_DS)) > > +#define __user_ok(addr, size) (((size) <= TASK_SIZE) \ > > + && ((addr) <= TASK_SIZE - (size))) > > +#define __access_ok(addr, size) (__kernel_ok || __user_ok((addr), (size))) > > A nice trick to simplify this is to introduce a per-process variable for comparing > the pointer, set_fs() then sets this variable to either TASK_SIZE or > UINT_MAX. Perhaps like this: 1. add a member named kaddr in thread_info 2. add following assignment codes in set_fs: current_thread_info()->kaddr = segment_eq(fs, KERNEL_DS) ? UINT_MAX : TASK_SIZE; 3. then __access_ok will be: #define addr #define __access_ok(addr, size) (((size) <= TASK_SIZE) \ && ((addr) <= current_thread_info()->kaddr) - (size))) > > This saves one conditional branch for each call to __access_ok. > > Arnd -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
