[Bug 237940] struct nvme_health_information_page{} @ /usr/include/dev/nvme/nvme.h has alignment issues.

bugzilla-noreply at freebsd.org bugzilla-noreply at freebsd.org
Fri May 17 18:21:03 UTC 2019


Conrad Meyer <cem at freebsd.org> changed:

           What    |Removed                     |Added
                 CC|                            |cem at freebsd.org

--- Comment #1 from Conrad Meyer <cem at freebsd.org> ---
Yes, the temperature field is inherently misaligned.

The __aligned(4) was added in r240671 as a hack for printing out the
nvme_controller_data and nvme_namespace_data pages as 32-bit hex values with a
naive cast -- avoiding a -Wcast-align warning.  At the time,
nvme_health_information_page wasn't used by nvmecontrol -- it was probably just
added at the same time because it was also __packed.

Today we mostly print the page using a specialized printer, print_log_health,
rather than any uint32 cast hex hack.  print_hex -> print_dwords still uses
this hack for the log page data if -x flag is specified, but print functions
take the raw void* buffer pointer rather than a structure pointer, so we can
probably drop the __aligned attribute.

Additionally, get_log_buffer() allocates the buffer using plain malloc() with
the log page size.  This implicitly provides 4-byte alignment because FreeBSD
only supports 32-bit and 64-bit architectures, and the log page is >4 bytes in
size, so any standard C compliant malloc must provide 4-byte alignment on any
platform FreeBSD runs on.  It might be more clear to use aligned_alloc() to
provide that guarantee explicitly instead, but I don't feel strongly about it.

Tl;dr: I think we can drop the __aligned(4) attribute now, and probably on the
other structures as well.

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