• Sumit Garg's avatar
    arm64: kgdb: Set PSTATE.SS to 1 to re-enable single-step · af6c0bd5
    Sumit Garg authored
    Currently only the first attempt to single-step has any effect. After
    that all further stepping remains "stuck" at the same program counter
    value.
    
    Refer to the ARM Architecture Reference Manual (ARM DDI 0487E.a) D2.12,
    PSTATE.SS=1 should be set at each step before transferring the PE to the
    'Active-not-pending' state. The problem here is PSTATE.SS=1 is not set
    since the second single-step.
    
    After the first single-step, the PE transferes to the 'Inactive' state,
    with PSTATE.SS=0 and MDSCR.SS=1, thus PSTATE.SS won't be set to 1 due to
    kernel_active_single_step()=true. Then the PE transferes to the
    'Active-pending' state when ERET and returns to the debugger by step
    exception.
    
    Before this patch:
    ==================
    Entering kdb (current=0xffff3376039f0000, pid 1) on processor 0 due to Keyboard Entry
    [0]kdb>
    
    [0]kdb>
    [0]kdb> bp write_sysrq_trigger
    Instruction(i) BP #0 at 0xffffa45c13d09290 (write_sysrq_trigger)
        is enabled   addr at ffffa45c13d09290, hardtype=0 installed=0
    
    [0]kdb> go
    $ echo h > /proc/sysrq-trigger
    
    Entering kdb (current=0xffff4f7e453f8000, pid 175) on processor 1 due to Breakpoint @ 0xffffad651a309290
    [1]kdb> ss
    
    Entering kdb (current=0xffff4f7e453f8000, pid 175) on processor 1 due to SS trap @ 0xffffad651a309294
    [1]kdb> ss
    
    Entering kdb (current=0xffff4f7e453f8000, pid 175) on processor 1 due to SS trap @ 0xffffad651a309294
    [1]kdb>
    
    After this patch:
    =================
    Entering kdb (current=0xffff6851c39f0000, pid 1) on processor 0 due to Keyboard Entry
    [0]kdb> bp write_sysrq_trigger
    Instruction(i) BP #0 at 0xffffc02d2dd09290 (write_sysrq_trigger)
        is enabled   addr at ffffc02d2dd09290, hardtype=0 installed=0
    
    [0]kdb> go
    $ echo h > /proc/sysrq-trigger
    
    Entering kdb (current=0xffff6851c53c1840, pid 174) on processor 1 due to Breakpoint @ 0xffffc02d2dd09290
    [1]kdb> ss
    
    Entering kdb (current=0xffff6851c53c1840, pid 174) on processor 1 due to SS trap @ 0xffffc02d2dd09294
    [1]kdb> ss
    
    Entering kdb (current=0xffff6851c53c1840, pid 174) on processor 1 due to SS trap @ 0xffffc02d2dd09298
    [1]kdb> ss
    
    Entering kdb (current=0xffff6851c53c1840, pid 174) on processor 1 due to SS trap @ 0xffffc02d2dd0929c
    [1]kdb>
    
    Fixes: 44679a4f ("arm64: KGDB: Add step debugging support")
    Co-developed-by: default avatarWei Li <liwei391@huawei.com>
    Signed-off-by: default avatarWei Li <liwei391@huawei.com>
    Signed-off-by: default avatarSumit Garg <sumit.garg@linaro.org>
    Tested-by: default avatarDouglas Anderson <dianders@chromium.org>
    Acked-by: default avatarDaniel Thompson <daniel.thompson@linaro.org>
    Tested-by: default avatarDaniel Thompson <daniel.thompson@linaro.org>
    Link: https://lore.kernel.org/r/20230202073148.657746-3-sumit.garg@linaro.orgSigned-off-by: default avatarWill Deacon <will@kernel.org>
    af6c0bd5
debug-monitors.c 10.7 KB