Re: [Qemu-devel] [PATCH v3 41/45] windbg: implemented kd_api_search_memory

[Ladi Prosek <lprosek@redhat.com>]

On Tue, Nov 21, 2017 at 3:11 PM, Mihail Abakumov
<mikhail.abakumov@ispras.ru> wrote:
> Signed-off-by: Mihail Abakumov <mikhail.abakumov@ispras.ru>
> Signed-off-by: Pavel Dovgalyuk <dovgaluk@ispras.ru>
> Signed-off-by: Dmitriy Koltunov <koltunov@ispras.ru>
> ---
>  include/exec/windbgstub-utils.h |    1 +
>  windbgstub-utils.c              |   33 +++++++++++++++++++++++++++++++++
>  windbgstub.c                    |    4 ++++
>  3 files changed, 38 insertions(+)
>
> diff --git a/include/exec/windbgstub-utils.h b/include/exec/windbgstub-utils.h
> index 73d49b774d..c2eb8a75a7 100755
> --- a/include/exec/windbgstub-utils.h
> +++ b/include/exec/windbgstub-utils.h
> @@ -102,6 +102,7 @@ void kd_api_write_physical_memory(CPUState *cpu, PacketData *pd);
>  void kd_api_get_version(CPUState *cpu, PacketData *pd);
>  void kd_api_read_msr(CPUState *cpu, PacketData *pd);
>  void kd_api_write_msr(CPUState *cpu, PacketData *pd);
> +void kd_api_search_memory(CPUState *cpu, PacketData *pd);
>  void kd_api_unsupported(CPUState *cpu, PacketData *pd);
>
>  SizedBuf kd_gen_exception_sc(CPUState *cpu);
> diff --git a/windbgstub-utils.c b/windbgstub-utils.c
> index 7ef301bac7..1f4590f338 100755
> --- a/windbgstub-utils.c
> +++ b/windbgstub-utils.c
> @@ -261,6 +261,39 @@ void kd_api_get_version(CPUState *cpu, PacketData *pd)
>      }
>  }
>
> +void kd_api_search_memory(CPUState *cpu, PacketData *pd)
> +{
> +    DBGKD_SEARCH_MEMORY *m64c = &pd->m64.u.SearchMemory;
> +    int s_len = MAX(ldq_p(&m64c->SearchLength), 1);
> +    int p_len = MIN(ldl_p(&m64c->PatternLength), pd->extra_size);
> +    target_ulong addr = ldq_p(&m64c->SearchAddress);
> +    int size = MIN(s_len, 10);
> +    uint8_t mem[size + p_len];

Is this allocation bounded by a reasonably small number? What's the
maximum PatternLength?

> +    int i, err;
> +
> +    pd->extra_size = 0;
> +    pd->m64.ReturnStatus = STATUS_NO_MORE_ENTRIES;
> +
> +    while (s_len) {
> +        err = cpu_memory_rw_debug(cpu, addr, mem, size + p_len, 0);
> +        if (!err) {
> +            for (i = 0; i < size; ++i) {
> +                if (memcmp(mem + i, pd->extra, p_len) == 0) {
> +                    stl_p(&m64c->FoundAddress, addr + i);
> +                    pd->m64.ReturnStatus = STATUS_SUCCESS;
> +                    return;
> +                }
> +            }
> +        } else {
> +            WINDBG_DEBUG("search_memory: No physical page mapped: " FMT_ADDR,
> +                         addr);
> +        }
> +        s_len -= size;
> +        addr += size;
> +        size = MIN(s_len, 10);
> +    }
> +}
> +

Too bad that you can't use memmem(). This implementation screams
O(N^2) to me. One of the things that can be improved later I guess.

I would at least up the step from 10 to 1024 so we don't call
cpu_memory_rw_debug() that often.

>  void kd_api_unsupported(CPUState *cpu, PacketData *pd)
>  {
>      WINDBG_ERROR("Caught unimplemented api %s",
> diff --git a/windbgstub.c b/windbgstub.c
> index 0268d0818e..d35ff6ba96 100755
> --- a/windbgstub.c
> +++ b/windbgstub.c
> @@ -212,6 +212,10 @@ static void windbg_process_manipulate_packet(ParsingContext *ctx)
>      case DbgKdClearAllInternalBreakpointsApi:
>          return;
>
> +    case DbgKdSearchMemoryApi:
> +        kd_api_search_memory(cpu, &ctx->data);
> +        break;
> +
>      default:
>          kd_api_unsupported(cpu, &ctx->data);
>          break;
>