On 12/17/19 12:59 PM, Heinrich Schuchardt wrote: > On 12/17/19 12:19 PM, Marek Vasut wrote: >> On 12/17/19 12:14 PM, Heinrich Schuchardt wrote: >>> On 12/17/19 11:00 AM, Marek Vasut wrote: >>>> On 12/17/19 10:27 AM, Heinrich Schuchardt wrote: >>>>> With GCC 9.2.1 errors of type -Werror=address-of-packed-member occur >>>>> when >>>>> passing a member of a packed structure to le16_to_cpus() on a big >>>>> endian >>>>> system (e.g. P2041RDB_defconfig). >>>>> >>>>> Replace le16_to_cpus() by get_unaligned_le16(). Check >>>>> defined(__BIG_ENDIAN) >>>>> to avoid the introduction of unnecessary instructions on little endian >>>>> systems as seen on aarch64. >>>> >>>> I would expect the compiler would optimize such stuff out ? >>>> Can we do without the ifdef ? >>> >>> When compiling qemu_arm64_defconfig without the #ifdef the GCC 9.2.1 >>> adds assembler instructions: >> >> Why ? >> > > I am not a GCC developer. I simply observed that GCC currently cannot > optimize this away on its own. That is why I added the #ifdef.
Are we now adding workarounds instead of solving issues properly? > Identifying that bit operations like << 8 in __get_unaligned_le16() have > zero effect is not an easy task when developing a compiler. You would > have to follow the flow of every bit. Maybe the fix is then to somehow optimize the get_unaligned_le16() to help the compiler ?
