• Martin Storsjö's avatar
    arm: Detect 32 bit cpu features on ARMv8 when running on a 64 bit kernel · 7b0c7c91
    Martin Storsjö authored
    When running on a 64 bit kernel, /proc/cpuinfo lists different
    optional features than on 32 bit kernels (because some of them
    are mandatory in the 64 bit implemenations).
    
    The kernel does list the old features properly if they are queried
    via /proc/self/auxv though - however this file is not always readable
    (e.g. on most android systems). The getauxval function could also
    provide the same info as /proc/self/auxv even if this file isn't
    readable, but this function is not always available (and thus would
    need to be loaded with dlsym for compatibility with older android
    versions).
    
    The android cpufeatures library does this slightly differently,
    by assuming that these are available if the "CPU architecture"
    line is >= 8, see [1] for details.
    
    It has been suggested to include the old, non-optional features in
    /proc/cpuinfo as well, but that suggested patch never was merged.
    See [2] for the discussion around this suggestion.
    
    [1] https://android-review.googlesource.com/91380
    [2] http://marc.info/?l=linux-arm-kernel&m=139087240101974Signed-off-by: 's avatarMartin Storsjö <martin@martin.st>
    7b0c7c91
cpu.c 4.16 KB