qemu /
qemu /
342368aff7d61a32b5853068b92039a2b15507c5 mips: Ensure PC update with MTC0 single-stepping
Correct the way PC is updated when single-stepping instructions, by
keeping the old PC only for the BS_EXCP (exception condition) state.
Some MTC0 (and possibly other) instructions switch to the BS_STOP state
to terminate the current translation block, so that the state transition
of the simulated CPU resulting from the CP0 operation takes effect with
the following instruction. This happens with `mtc0 <reg>,c0_config' for
example, typically used to set KSEG0 cacheability.
While single-stepping this has a side-effect of not advancing the PC
past the instruction just executed; subsequent single-step traps will
stop at the same instruction repeatedly. Example:
(gdb) stepi
0x80004d24 in _start ()
5: x/i $pc
=> 0x80004d24 <_start+364>: mfc0 t1,c0_config
(gdb)
0x80004d28 in _start ()
5: x/i $pc
=> 0x80004d28 <_start+368>: li at,-8
(gdb)
0x80004d2c in _start ()
5: x/i $pc
=> 0x80004d2c <_start+372>: and t1,t1,at
(gdb)
0x80004d30 in _start ()
5: x/i $pc
=> 0x80004d30 <_start+376>: ori t1,t1,0x3
(gdb)
0x80004d34 in _start ()
5: x/i $pc
=> 0x80004d34 <_start+380>: mtc0 t1,c0_config
(gdb)
0x80004d34 in _start ()
5: x/i $pc
=> 0x80004d34 <_start+380>: mtc0 t1,c0_config
(gdb)
0x80004d34 in _start ()
5: x/i $pc
=> 0x80004d34 <_start+380>: mtc0 t1,c0_config
(gdb)
0x80004d34 in _start ()
5: x/i $pc
=> 0x80004d34 <_start+380>: mtc0 t1,c0_config
(gdb)
-- oops!
Signed-off-by: Maciej W. Rozycki <macro@codesourcery.com>
Reviewed-by: Leon Alrae <leon.alrae@imgtec.com>
Signed-off-by: Leon Alrae <leon.alrae@imgtec.com>
1 file changed
