Re: [Crash-utility] Faster iteration on list of struct.field
----- Original Message -----
Dave Anderson wrote on Wed, Feb 05, 2020:
> > What might make sense is to use the "struct -r" option, which does a
raw
> > memory dump of a data structure. But for a reason I do not recall, it
> > prevents that option from being used with a "struct_name.field"
argument.
> > (see line 6628 of symbols.c). But I don't see why that couldn't be
made
> > to work, though, since the end result is simply a call to
> > raw_data_dump().
I'll give this a try tomorrow, probably just needs to add
dm->member_offset to addr and dump dm->member_size long value, that
looks straightforward enough.
> ...and then if you get "struct -r" to work with a
"struct_name.field"
> argument, the next challenge would be the caching aspect of your request.
>
> Currently there's no manner in which command-specific information is
> cached beyond the execution of a single command. With "< file", the
> command gets executed from scratch each time.
That does look more challenging... Or rather more a matter of taste? a
kludge probably wouldn't be so bad to put in, but it's probably better
to have something more generic than making 'datatype_member' static in
cmd_datatype_common (well, it needs a bit more than that as the argument
strings won't be useable from one call to the next...)
I assume the slow part in this will be the member_to_datatype call in
do_datatype_addr? I'll first confirm that's the only slow bit, if there
is only one spot to optimize away it might not be so bad.
But yeah, without caching I don't think it's realistic; and making the
'< file' construct iterate within the function looks more work than
trying to make struct cache some info.
Thanks!
Right, the time-consumer is the call into gdb to get the structure member details.
I'm not following what you mean by "making 'datatype_member' static
...", but
off the top of my head, I was thinking of adding a "tmp_offset" and
"tmp_size"
fields to the global offset_table and size_table structures, and adding a new
pc->curcmd_flags bit. Then, if a command that wants to support such a concept,
it could:
(1) check the new pc->curcmd_flags bit, which will always be 0 the first time
the function gets called by the exec_args_input_file() loop.
(2) if the new bit is 0, then set OFFSET(tmp_offset) and SIZE(tmp_size)
(3) set the new flag in pc->curcmd_flags, and continue...
Then during the second and subsequent times through the loop, pc->curcmd_flags
will still be set/unchanged, because restore_sanity() is not called from the
exec_args_input_flags() loop.
But that scheme falls down if a user requests a comma-separated list of
multiple members (argc_members would be > 1). Although, it might be better
if the "struct -r' option rejects multiple-member arguments, especially given
that the output would be pretty much unreadable.
Dave
--
Dominique
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