On Tue, Oct 5, 2021 at 9:15 AM Ard Biesheuvel [off-list ref] wrote:

The current irq_handler macro uses a literal load followed by an
explicit assignment of lr before an indirect call, both of which are
sub-optimal on recent ARM cores. Replace it by a mov_l call, which will
evaluate to a movw/movt pair on v7 cores, avoiding one of the two loads,
followed by a call to a newly introduced 'bl_m' macro, which will
evaluate to a blx instruction on cores that support it. (Setting lr
explicitly rather than via a bl or blx instruction confuses the return
address prediction that modern out-of-order cores use to speculatively
perform the function return.)

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>

Reviewed-by: Arnd Bergmann <arnd@arndb.de>

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