On 03/16/2016 05:39 PM, Arnd Bergmann wrote: > A bug in the gcc-6.0 prerelease version caused at least one > driver (lpfc) to have excessive stack usage when dealing with > wwn data, on the ARM architecture. > > lpfc_scsi.c: In function 'lpfc_find_next_oas_lun': > lpfc_scsi.c:117:1: warning: the frame size of 1152 bytes is larger than 1024 bytes [-Wframe-larger-than=] > > I have reported this as a gcc regression in > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70232 > > However, using a better implementation of wwn_to_u64() not only > helps with the particular gcc problem but also leads to better > object code for any version or architecture. > > The kernel already provides get_unaligned_be64() and > put_unaligned_be64() helper functions that provide an > optimized implementation with the desired semantics. > > The lpfc_find_next_oas_lun() function in the example that > grew from 1146 bytes to 5144 bytes when moving from gcc-5.3 > to gcc-6.0 is now 804 bytes, as the optimized > get_unaligned_be64() load can be done in three instructions. > The stack usage is now down to 28 bytes from 128 bytes with > gcc-5.3 before. > > Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx> > --- > include/scsi/scsi_transport_fc.h | 15 +++------------ > 1 file changed, 3 insertions(+), 12 deletions(-) > Reviewed-by: Hannes Reinecke <hare@xxxxxxxx> Cheers, Hannes -- Dr. Hannes Reinecke Teamlead Storage & Networking hare@xxxxxxx +49 911 74053 688 SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg GF: F. Imendörffer, J. Smithard, J. Guild, D. Upmanyu, G. Norton HRB 21284 (AG Nürnberg) -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
