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bhyve: Appease warning about a potentially unaligned pointer.
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Authored by jhb on Wed, Nov 23, 11:16 PM.
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Summary

When initializing the device model for a PCI pass through device that
uses MSI-X, bhyve reads the MSI-X capability from the real device to
save a copy in the emulated PCI config space. It also saves a copy in
a local struct msixcap on the stack. Since struct msixcap is packed,
GCC complains that casting a pointer to the struct to a uint32_t
pointer may result in an unaligned pointer.

This path is not performance critical, so to appease the compiler,
simply change the pointer to a char * and use memcpy to copy the 4
bytes read in each iteration of the loop.

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jhb requested review of this revision.Wed, Nov 23, 11:16 PM

I realize the person from illumos might have had a different fix for this, but I think this might be the cleanest of the options. I tried adding an __Alignas(4) on the local variable and that didn't appease GCC's warning here.

This revision is now accepted and ready to land.Thu, Nov 24, 6:38 AM