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Arnd Bergmann authored
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@arndb.de> Reviewed-by:
Hannes Reinicke <hare@suse.de> Reviewed-by:
Ewan Milne <emilne@redhat.com> Signed-off-by:
Martin K. Petersen <martin.petersen@oracle.com>
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