On Tue, Nov 18, 2014 at 02:34:56PM +0800, bin.jiang@xxxxxxxxxxxxx wrote: > From: Bin Jiang <bin.jiang@xxxxxxxxxxxxx> > > The following compile warning is caused to use uninitialized variables: > > fs/compat_ioctl.c: In function 'compat_SyS_ioctl': > arch/mips/include/asm/uaccess.h:451:2: warning: 'length' may be used \ > uninitialized in this function [-Wmaybe-uninitialized] > __asm__ __volatile__( \ > ^ > fs/compat_ioctl.c:208:6: note: 'length' was declared here > int length, err; > ^ > > In get_user function, the parameter @x is used to store result. If the > function return error, the @x won't be set and cause above warning. > > According to the description of get_user function, the parameter @x should > be set to zero on error. You're not the first to send such a patch, see http://patchwork.linux-mips.org/patch/1307/ However I've hesistated to apply the previous patch which only claimed to resolve a warning because __get_user and get_user get expanded very often in the kernel so a small innocent looking change like this results in a surprisingly large bloat. A smart compiler will reorder this: int x; if (...) { ... } else x = 0; into: int x = 0; if (...) { ... } Which avoids the branches otherwise necessary for the else construct. However both the original and your patch fail to take care of the case where the if is taken but __get_user_asm aborts due to an inaccessible fault. That case is only fixed by manually doing above reordering - a compiler can't know that the inline assembler won't assign anything in that case. The comment btw was cut and paste and - blame me - it seems I failed to read what it promises about @x for the error case; I had implemented get_user under the assumption that the returned value was undefined in case of an -EFAULT error. Thanks for reporting this! Ralf
