The old implementation replaces two insns, swapping between
b <dest>
nop
and
pcaddu18i tmp, <dest>
jirl zero, tmp, <dest> & 0xffff
There is a race condition in which a thread could be stopped at
the jirl, i.e. with the top of the address loaded, and when
restarted we have re-linked to a different TB, so that the top
half no longer matches the bottom half.
Note that while we never directly re-link to a different TB, we
can link, unlink, and link again all while the stopped thread
remains stopped.
The new implementation replaces only one insn, swapping between
b <dest>
and
pcadd tmp, <jmp_addr>
falling through to load the address from tmp, and branch.
Reviewed-by: WANG Xuerui <git@xen0n.name>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
709bcd7da3