Re: [patch v8 17/24] record-btrace: provide xfer_partial target method

Pedro Alves
2013-12-13T18:43:43Z

On 12/12/2013 09:15 AM, Markus Metzger wrote:
> Provide the xfer_partial target method for the btrace record target.
>
> Only allow memory accesses to readonly memory while we're replaying.
>
> 2013-12-12 Markus Metzger <markus.t.metzger@intel.com>
>
> * record-btrace.c (record_btrace_xfer_partial): New.
> (init_record_btrace_ops): Initialize xfer_partial.
>
>
> ---
> gdb/record-btrace.c | 51 +++++++++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 51 insertions(+)
>
> diff --git a/gdb/record-btrace.c b/gdb/record-btrace.c
> index cf30e17..ec99ba2 100644
> --- a/gdb/record-btrace.c
> +++ b/gdb/record-btrace.c
> @@ -753,6 +753,56 @@ record_btrace_is_replaying (void)
> return 0;
> }
>
> +/* The to_xfer_partial method of target record-btrace. */
> +
> +static LONGEST
> +record_btrace_xfer_partial (struct target_ops *ops, enum target_object object,
> + const char *annex, gdb_byte *readbuf,
> + const gdb_byte *writebuf, ULONGEST offset,
> + LONGEST len)
> +{
> + struct target_ops *t;
> +
> + /* Filter out requests that don't make sense during replay. */

This allows writes to pass through?

> + if (record_btrace_is_replaying ())
> + {
> + switch (object)
> + {
> + case TARGET_OBJECT_MEMORY:
> + case TARGET_OBJECT_RAW_MEMORY:
> + case TARGET_OBJECT_STACK_MEMORY:

I don't think we actually ever see TARGET_OBJECT_RAW_MEMORY
and TARGET_OBJECT_STACK_MEMORY here? Those are supposedly
handled by target.c, and translated to TARGET_OBJECT_MEMORY
before reaching the actual targets.

> + {
> + /* We allow reading readonly memory. */
> + struct target_section *section;

A comment on this being an heuristic would be good. The _current_
readonly sections might well not be the same as the ones the
target had when the trace was recorded.

> +
> + section = target_section_by_addr (ops, offset);
> + if (section != NULL)
> + {
> + /* Check if the section we found is readonly. */
> + if ((bfd_get_section_flags (section->the_bfd_section->owner,
> + section->the_bfd_section)
> + & SEC_READONLY) != 0)
> + {
> + /* Truncate the request to fit into this section. */
> + len = min (len, section->endaddr - offset);
> + break;
> + }
> + }
> +
> + return -1;

I must be missing something, but won't raw_memory_xfer_partial
keep trying in the target beneath, anyway?

> + }
> + }
> + }
> +
> + /* Forward the request. */
> + for (t = ops->beneath; t != NULL; t = t->beneath)
> + if (t->to_xfer_partial != NULL)
> + return t->to_xfer_partial (t, object, annex, readbuf, writebuf,
> + offset, len);
> +
> + return -1;
> +}
> +
> /* The to_fetch_registers method of target record-btrace. */
>
> static void
> @@ -930,6 +980,7 @@ init_record_btrace_ops (void)
> ops->to_call_history_from = record_btrace_call_history_from;
> ops->to_call_history_range = record_btrace_call_history_range;
> ops->to_record_is_replaying = record_btrace_is_replaying;
> + ops->to_xfer_partial = record_btrace_xfer_partial;
> ops->to_fetch_registers = record_btrace_fetch_registers;
> ops->to_store_registers = record_btrace_store_registers;
> ops->to_prepare_to_store = record_btrace_prepare_to_store;
>

--
Pedro Alves