Re: [Qemu-devel] [PATCH 3/3 v2] ppc debug: Add debug stub support

[address@hidden]

> -----Original Message-----
> From: Alexander Graf [mailto:address@hidden
> Sent: Tuesday, June 17, 2014 3:20 PM
> To: Bhushan Bharat-R65777; address@hidden; address@hidden
> Subject: Re: [PATCH 3/3 v2] ppc debug: Add debug stub support
> 
> 
> On 17.06.14 11:14, address@hidden wrote:
> >
> >> -----Original Message-----
> >> From: Alexander Graf [mailto:address@hidden
> >> Sent: Tuesday, June 17, 2014 1:46 PM
> >> To: Bhushan Bharat-R65777; address@hidden; address@hidden
> >> Subject: Re: [PATCH 3/3 v2] ppc debug: Add debug stub support
> >>
> >>
> >> On 17.06.14 09:08, Bharat Bhushan wrote:
> >>> This patch adds software breakpoint, hardware breakpoint and
> >>> hardware watchpoint support for ppc. If the debug interrupt is not
> >>> handled then this is injected to guest.
> >>>
> >>> Signed-off-by: Bharat Bhushan <address@hidden>
> >>> ---
> >>> v1->v2:
> >>>    - factored out e500 specific code based on exception model
> >> POWERPC_EXCP_BOOKE.
> >>>    - Not supporting ppc440
> >>>
> >>>    hw/ppc/e500.c        |   3 +
> >>>    target-ppc/kvm.c     | 355
> ++++++++++++++++++++++++++++++++++++++++++++++---
> >> --
> >>>    target-ppc/kvm_ppc.h |   1 +
> >>>    3 files changed, 330 insertions(+), 29 deletions(-)
> >>>
> >>> diff --git a/hw/ppc/e500.c b/hw/ppc/e500.c index a973c18..47caa84
> >>> 100644
> >>> --- a/hw/ppc/e500.c
> >>> +++ b/hw/ppc/e500.c
> >>> @@ -853,6 +853,9 @@ void ppce500_init(MachineState *machine,
> >>> PPCE500Params
> >> *params)
> >>>        if (kvm_enabled()) {
> >>>            kvmppc_init();
> >>>        }
> >>> +
> >>> +    /* E500 supports 2 h/w breakpoints and 2 watchpoints */
> >>> +    kvmppc_hw_breakpoint_init(2, 2);
> >> This does not belong into the machine file.
> > What about calling this from init_proc_e500() in 
> > target-ppc/translate_init.c ?
> 
> I think it makes sense to leave it in KVM land. Why not do it lazily on
> insert_hw_breakpoint?

You mean setting in kvm_arch_insert_hw_breakpoint() when called first time; 
something like:

    static bool init = 0;

    if (!init) {
        if (env->excp_model == POWERPC_EXCP_BOOKE) {
            max_hw_breakpoint = 2;
            max_hw_watchpoint = 2;
        } else
           // Add for book3s max_hw_watchpoint = 1;
         }
         init = 1;
    }

> 
> >
> >>>    }
> >>>
> >>>    static int e500_ccsr_initfn(SysBusDevice *dev) diff --git
> >>> a/target-ppc/kvm.c b/target-ppc/kvm.c index 70f77d1..994a618 100644
> >>> --- a/target-ppc/kvm.c
> >>> +++ b/target-ppc/kvm.c
> >>> @@ -38,6 +38,7 @@
> >>>    #include "hw/ppc/ppc.h"
> >>>    #include "sysemu/watchdog.h"
> >>>    #include "trace.h"
> >>> +#include "exec/gdbstub.h"
> >>>
> >>>    //#define DEBUG_KVM
> >>>
> >>> @@ -759,11 +760,55 @@ static int kvm_put_vpa(CPUState *cs)
> >>>    }
> >>>    #endif /* TARGET_PPC64 */
> >>>
> >>> -static int kvmppc_inject_debug_exception(CPUState *cs)
> >>> +static int kvmppc_e500_inject_debug_exception(CPUState *cs)
> >>>    {
> >>> +    PowerPCCPU *cpu = POWERPC_CPU(cs);
> >>> +    CPUPPCState *env = &cpu->env;
> >>> +    struct kvm_sregs sregs;
> >>> +    int ret;
> >>> +
> >>> +    if (!cap_booke_sregs) {
> >>> +        return -1;
> >>> +    }
> >>> +
> >>> +    ret = kvm_vcpu_ioctl(cs, KVM_GET_SREGS, &sregs);
> >>> +    if (ret < 0) {
> >>> +        return -1;
> >>> +    }
> >>> +
> >>> +    if (sregs.u.e.features & KVM_SREGS_E_ED) {
> >>> +        sregs.u.e.dsrr0 = env->nip;
> >>> +        sregs.u.e.dsrr1 = env->msr;
> >>> +    } else {
> >>> +        sregs.u.e.csrr0 = env->nip;
> >>> +        sregs.u.e.csrr1 = env->msr;
> >>> +    }
> >>> +
> >>> +    sregs.u.e.update_special = KVM_SREGS_E_UPDATE_DBSR;
> >>> +    sregs.u.e.dbsr = env->spr[SPR_BOOKE_DBSR];
> >>> +
> >>> +    ret = kvm_vcpu_ioctl(cs, KVM_SET_SREGS, &sregs);
> >>> +    if (ret < 0) {
> >>> +        return -1;
> >>> +    }
> >>> +
> >>> +    env->pending_interrupts &= ~(1 << PPC_INTERRUPT_DEBUG);
> >> I think it makes sense to move this into kvmppc_inject_exception().
> >> Then we have everything dealing with pending_interrupts in one spot.
> > Will do
> >
> >>> +
> >>>        return 0;
> >>>    }
> >>>
> >>> +static int kvmppc_inject_debug_exception(CPUState *cs) {
> >>> +    PowerPCCPU *cpu = POWERPC_CPU(cs);
> >>> +    CPUPPCState *env = &cpu->env;
> >>> +
> >>> +    if (env->excp_model == POWERPC_EXCP_BOOKE) {
> >>> +        return kvmppc_e500_inject_debug_exception(cs);
> >>> +    }
> >> Yes, exactly the way I wanted to see it :). Please make this a switch
> >> though - that'll make it easier for others to plug in later.
> > Will do
> >
> >>> +
> >>> +    return -1;
> >>> +}
> >>> +
> >>>    static void kvmppc_inject_exception(CPUState *cs)
> >>>    {
> >>>        PowerPCCPU *cpu = POWERPC_CPU(cs); @@ -1268,6 +1313,276 @@
> >>> static int kvmppc_handle_dcr_write(CPUPPCState *env, uint32_t dcrn,
> >>> uint32_t
> >> dat
> >>>        return 0;
> >>>    }
> >>>
> >>> +int kvm_arch_insert_sw_breakpoint(CPUState *cs, struct
> >>> +kvm_sw_breakpoint *bp) {
> >>> +    /* Mixed endian case is not handled */
> >>> +    uint32_t sc = debug_inst_opcode;
> >>> +
> >>> +    if (cpu_memory_rw_debug(cs, bp->pc, (uint8_t *)&bp->saved_insn, 4, 0)
> ||
> >>> +        cpu_memory_rw_debug(cs, bp->pc, (uint8_t *)&sc, 4, 1)) {
> >>> +        return -EINVAL;
> >>> +    }
> >>> +
> >>> +    return 0;
> >>> +}
> >>> +
> >>> +int kvm_arch_remove_sw_breakpoint(CPUState *cs, struct
> >>> +kvm_sw_breakpoint *bp) {
> >>> +    uint32_t sc;
> >>> +
> >>> +    if (cpu_memory_rw_debug(cs, bp->pc, (uint8_t *)&sc, 4, 0) ||
> >>> +        sc != debug_inst_opcode ||
> >>> +        cpu_memory_rw_debug(cs, bp->pc, (uint8_t *)&bp->saved_insn, 4, 
> >>> 1))
> {
> >>> +        return -EINVAL;
> >>> +    }
> >>> +
> >>> +    return 0;
> >>> +}
> >>> +
> >>> +#define MAX_HW_BKPTS 4
> >>> +
> >>> +static struct HWBreakpoint {
> >>> +    target_ulong addr;
> >>> +    int type;
> >>> +} hw_breakpoint[MAX_HW_BKPTS];
> >> This struct contains both watchpoints and breakpoints, no? It really
> >> should be named accordingly. Maybe only call them points? Not sure :).
> > May be hw_debug_points/ hw_wb_points :)
> >
> >>> +
> >>> +static CPUWatchpoint hw_watchpoint;
> >> What is this?
> > This struct needed to be passed to debugstub when watchpoint triggered. 
> > Please
> see debug_handler.
> 
> Man, this is ugly :).

Yes, this is how x86 also works.
May be we move this in debug_handler function but ensure to keep it static.

> 
> >
> >>> +
> >>> +/* Default there is no breakpoint and watchpoint supported */
> >>> +static int max_hw_breakpoint; static int max_hw_watchpoint; static
> >>> +int nb_hw_breakpoint; static int nb_hw_watchpoint;
> >>> +
> >>> +void kvmppc_hw_breakpoint_init(int num_breakpoints, int
> >>> +num_watchpoints) {
> >>> +    if ((num_breakpoints + num_watchpoints) > MAX_HW_BKPTS) {
> >>> +        fprintf(stderr, "Error initializing h/w breakpints\n");
> >> breakpoints?
> > "debug break/watch_points"
> 
> You have a typo.
> 
> >
> >>> +        return;
> >>> +    }
> >>> +
> >>> +    max_hw_breakpoint = num_breakpoints;
> >>> +    max_hw_watchpoint = num_watchpoints; }
> >>> +
> >>> +static int find_hw_breakpoint(target_ulong addr, int type) {
> >>> +    int n;
> >>> +
> >>> +    for (n = 0; n < nb_hw_breakpoint + nb_hw_watchpoint; n++) {
> >>> +        if (hw_breakpoint[n].addr == addr && hw_breakpoint[n].type == 
> >>> type)
> {
> >>> +            return n;
> >>> +        }
> >>> +    }
> >>> +
> >>> +    return -1;
> >>> +}
> >>> +
> >>> +static int find_hw_watchpoint(target_ulong addr, int *flag) {
> >>> +    int n;
> >>> +
> >>> +    n = find_hw_breakpoint(addr, GDB_WATCHPOINT_ACCESS);
> >>> +    if (n >= 0) {
> >>> +        *flag = BP_MEM_ACCESS;
> >>> +        return n;
> >>> +    }
> >>> +
> >>> +    n = find_hw_breakpoint(addr, GDB_WATCHPOINT_WRITE);
> >>> +    if (n >= 0) {
> >>> +        *flag = BP_MEM_WRITE;
> >>> +        return n;
> >>> +    }
> >>> +
> >>> +    n = find_hw_breakpoint(addr, GDB_WATCHPOINT_READ);
> >>> +    if (n >= 0) {
> >>> +        *flag = BP_MEM_READ;
> >>> +        return n;
> >>> +    }
> >>> +
> >>> +    return -1;
> >>> +}
> >>> +
> >>> +int kvm_arch_insert_hw_breakpoint(target_ulong addr,
> >>> +                                  target_ulong len, int type) {
> >> Boundary check?
> > Yes, Good catch
> >
> >>> +    hw_breakpoint[nb_hw_breakpoint + nb_hw_watchpoint].addr = addr;
> >>> +    hw_breakpoint[nb_hw_breakpoint + nb_hw_watchpoint].type = type;
> >>> +
> >>> +    switch (type) {
> >>> +    case GDB_BREAKPOINT_HW:
> >>> +        if (nb_hw_breakpoint >= max_hw_breakpoint) {
> >>> +            return -ENOBUFS;
> >>> +        }
> >>> +
> >>> +        if (find_hw_breakpoint(addr, type) >= 0) {
> >>> +            return -EEXIST;
> >>> +        }
> >>> +
> >>> +        nb_hw_breakpoint++;
> >>> +        break;
> >>> +
> >>> +    case GDB_WATCHPOINT_WRITE:
> >>> +    case GDB_WATCHPOINT_READ:
> >>> +    case GDB_WATCHPOINT_ACCESS:
> >>> +        if (nb_hw_watchpoint >= max_hw_watchpoint) {
> >>> +            return -ENOBUFS;
> >>> +        }
> >>> +
> >>> +        if (find_hw_breakpoint(addr, type) >= 0) {
> >>> +            return -EEXIST;
> >>> +        }
> >>> +
> >>> +        nb_hw_watchpoint++;
> >>> +        break;
> >>> +
> >>> +    default:
> >>> +        return -ENOSYS;
> >>> +    }
> >>> +
> >>> +    return 0;
> >>> +}
> >>> +
> >>> +int kvm_arch_remove_hw_breakpoint(target_ulong addr,
> >>> +                                  target_ulong len, int type) {
> >>> +    int n;
> >>> +
> >>> +    n = find_hw_breakpoint(addr, type);
> >>> +    if (n < 0) {
> >>> +        return -ENOENT;
> >>> +    }
> >>> +
> >>> +    switch (type) {
> >>> +    case GDB_BREAKPOINT_HW:
> >>> +        nb_hw_breakpoint--;
> >>> +        break;
> >>> +
> >>> +    case GDB_WATCHPOINT_WRITE:
> >>> +    case GDB_WATCHPOINT_READ:
> >>> +    case GDB_WATCHPOINT_ACCESS:
> >>> +        nb_hw_watchpoint--;
> >>> +        break;
> >>> +
> >>> +    default:
> >>> +        return -ENOSYS;
> >>> +    }
> >>> +    hw_breakpoint[n] = hw_breakpoint[nb_hw_breakpoint +
> >>> + nb_hw_watchpoint];
> >>> +
> >>> +    return 0;
> >>> +}
> >>> +
> >>> +void kvm_arch_remove_all_hw_breakpoints(void)
> >>> +{
> >>> +    nb_hw_breakpoint = nb_hw_watchpoint = 0; }
> >>> +
> >>> +static int kvm_e500_handle_debug(PowerPCCPU *cpu, struct kvm_run
> >>> +*run) {
> >>> +    CPUState *cs = CPU(cpu);
> >>> +    CPUPPCState *env = &cpu->env;
> >>> +    int handle = 0;
> >>> +    int n;
> >>> +    int flag = 0;
> >>> +    struct kvm_debug_exit_arch *arch_info = &run->debug.arch;
> >>> +
> >>> +    if (nb_hw_breakpoint + nb_hw_watchpoint > 0) {
> >>> +        if (arch_info->status & KVMPPC_DEBUG_BREAKPOINT) {
> >>> +            n = find_hw_breakpoint(arch_info->address, 
> >>> GDB_BREAKPOINT_HW);
> >>> +            if (n >= 0) {
> >>> +                handle = 1;
> >>> +            }
> >>> +        } else if (arch_info->status & (KVMPPC_DEBUG_WATCH_READ |
> >>> +                                        KVMPPC_DEBUG_WATCH_WRITE)) {
> >>> +            n = find_hw_watchpoint(arch_info->address,  &flag);
> >>> +            if (n >= 0) {
> >>> +                handle = 1;
> >>> +                cs->watchpoint_hit = &hw_watchpoint;
> >>> +                hw_watchpoint.vaddr = hw_breakpoint[n].addr;
> >>> +                hw_watchpoint.flags = flag;
> >>> +            }
> >>> +        }
> >>> +    }
> >> I think the above could easily be shared with book3s. Please put it
> >> into a helper function.
> > This is something I am not sure about, may be book3s was to interpret " 
> > struct
> kvm_debug_exit_arch *arch_info" in different way ?
> > So I left this booke specific. When someone implements h/w break/watch_point
> on book3s then he can decide to re-use this if it fits.
> 
> Let's assume it's generic for now. That way we maybe have a slight change to
> push the IBM guys into the right direction ;).

Ok :)
I will mention that this is untested in book3s

> 
> >
> >>> +
> >>> +    cpu_synchronize_state(cs);
> >>> +    if (handle) {
> >>> +        env->spr[SPR_BOOKE_DBSR] = 0;
> >>> +    } else {
> >>> +       printf("unhandled\n");
> >> This debug output would spawn every time the guest does in-guest debugging,
> no?
> >> Please remove it.
> > Yes, Will remove
> >
> >>> +       /* inject debug exception into guest */
> >>> +       env->pending_interrupts |=  1 << PPC_INTERRUPT_DEBUG;
> >>> +    }
> >>> +
> >>> +    return handle;
> >>> +}
> >>> +
> >>> +static void kvm_arch_e500_update_guest_debug(CPUState *cs,
> >>> +                                             struct kvm_guest_debug
> >>> +*dbg) {
> >>> +    int n;
> >>> +
> >>> +    if (nb_hw_breakpoint + nb_hw_watchpoint > 0) {
> >>> +        dbg->control |= KVM_GUESTDBG_ENABLE | KVM_GUESTDBG_USE_HW_BP;
> >>> +        memset(dbg->arch.bp, 0, sizeof(dbg->arch.bp));
> >>> +        for (n = 0; n < nb_hw_breakpoint + nb_hw_watchpoint; n++) {
> >> Boundary check against dbg->arch.bp missing.
> > Did not get, what you mean by " dbg->arch.bp missing" ?
> 
> dbg->arch.bp is an array of a certain size. If nb_hw_breakpoint +
> nb_hw_watchpoint > ARRAY_SIZE(dbg->arch.bp) we might overwrite memory we don't
> want to overwrite.

Actually this will never overflow here because nb_hw_breakpoint and 
nb_hw_watchpoint overflow in taken care in in hw_insert_breakpoint().
Do you thing that to be double safe we can add a check?

> 
> >
> >>> +            switch (hw_breakpoint[n].type) {
> >>> +            case GDB_BREAKPOINT_HW:
> >>> +                dbg->arch.bp[n].type = KVMPPC_DEBUG_BREAKPOINT;
> >>> +                break;
> >>> +            case GDB_WATCHPOINT_WRITE:
> >>> +                dbg->arch.bp[n].type = KVMPPC_DEBUG_WATCH_WRITE;
> >>> +                break;
> >>> +            case GDB_WATCHPOINT_READ:
> >>> +                dbg->arch.bp[n].type = KVMPPC_DEBUG_WATCH_READ;
> >>> +                break;
> >>> +            case GDB_WATCHPOINT_ACCESS:
> >>> +                dbg->arch.bp[n].type = KVMPPC_DEBUG_WATCH_WRITE |
> >>> +                                        KVMPPC_DEBUG_WATCH_READ;
> >>> +                break;
> >>> +            default:
> >>> +                cpu_abort(cs, "Unsupported breakpoint type\n");
> >>> +            }
> >>> +            dbg->arch.bp[n].addr = hw_breakpoint[n].addr;
> >>> +        }
> >>> +    }
> >> I think this function is pretty universal, no?
> > Again I was not sure that about this, may be book3s wants to use "struct
> kvm_guest_debug {" differently. This has extension like DABRX etc, So may be
> they want to may then in this register. So I left to the developer to decide.
> 
> They can't have their own struct kvm_guest_debug, so I really think this 
> should
> be shared.

Maybe they use different encoding in type and accordingly other elements of 
struct. But I am fine to assume they will use as is and then change if needed.

Thanks
-Bharat

> 
> 
> Alex