[PATCH 1/1] usb: avoid -Werror=address-of-packed-member

[Heinrich Schuchardt]

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:

         /* correct le values */
         dev->descriptor.bcdUSB =
   48:   79020660        strh    w0, [x19, #258]
   4c:   39442660        ldrb    w0, [x19, #265]
   50:   2a002020        orr     w0, w1, w0, lsl #8
   54:   39442a61        ldrb    w1, [x19, #266]
                 get_unaligned_le16(&dev->descriptor.bcdUSB);
         dev->descriptor.idVendor =
   58:   79021260        strh    w0, [x19, #264]
   5c:   39442e60        ldrb    w0, [x19, #267]
   60:   2a002020        orr     w0, w1, w0, lsl #8
   64:   39443261        ldrb    w1, [x19, #268]
                 get_unaligned_le16(&dev->descriptor.idVendor);
         dev->descriptor.idProduct =
   68:   79021660        strh    w0, [x19, #266]
   6c:   39443660        ldrb    w0, [x19, #269]
   70:   2a002020        orr     w0, w1, w0, lsl #8
                 get_unaligned_le16(&dev->descriptor.idProduct);
         dev->descriptor.bcdDevice =
   74:   79021a60        strh    w0, [x19, #268]
         udelay(1000 * msec);
   78:   d2807d00        mov     x0, #0x3e8                      // #1000
   7c:   94000000        bl      0 <udelay>
          * one microframe duration here (1mS for USB 1.x , 125uS for
USB 2.0).
          */
         mdelay(1);

Best regards

Heinrich