qemu /
qemu /
9b6a3ea7a699594162ed3d11e4e04b98568dc5c0 target-arm: Correctly handle 'sub pc, pc, 1' for ARMv6
In the ARM v6 architecture, 'sub pc, pc, 1' is not an interworking
branch, so the computed new value is written to r15 as a normal
value. The architecture says that in this case, bits [1:0] of
the value written must be ignored if we are in ARM mode (or
bit [0] ignored if in Thumb mode); this is a change from the
ARMv4/v5 specification that behaviour is UNPREDICTABLE.
Use the correct mask on the PC value when doing a non-interworking
store to PC.
A popular library used on RaspberryPi uses this instruction
as part of a trick to determine whether it is running on
ARMv6 or ARMv7, and we were mishandling the sequence.
Fixes bug: https://bugs.launchpad.net/bugs/1625295
Reported-by: <stu.axon@gmail.com>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 1474380941-4730-1-git-send-email-peter.maydell@linaro.org
1 file changed
