Re: [tcf-dev] Possible issue with symbols proxy

[Eugene Tarassov <eugene.tarassov@xxxxxxxxxx>]

Hi Benoit,

We don't use symbols groups, so I don't have a way to test and validate such changes. I would rather keep it as is than risk to break something. In this case, performance impact of extra flush is negligible, but if we end up with not flushing something that needs to be flushed, we will get a serious problem.

Regards,
Eugene

-----Original Message-----
From: Benoit Perrin [mailto:benoit.perrin@xxxxxxxxxxxxx]
Sent: Thursday, April 10, 2014 12:20 AM
To: Eugene Tarassov
Cc: TCF Development
Subject: Re: [tcf-dev] Possible issue with symbols proxy

Hi Eugene,

I don't see other problems than this too aggressive symbol flush. But as found
it strange, I was thinking of a bug. I agree that the data will be requested the
next time.

Do you want me to create a bugzilla for an enhancement request?

Thanks for the quick reply.

Benoit

On 04/08/2014 9:16 PM, Eugene Tarassov wrote:
> Hi Benoit,
>
> Flushing symbol info in this case might be suboptimal - too aggressive, but should not cause problems. The info should be re-requested when the cache item is notified. Do you see any problems beside suboptimal behavior?
>
> Regards,
> Eugene
>
> -----Original Message-----
> From: tcf-dev-bounces@xxxxxxxxxxx [mailto:tcf-dev-bounces@xxxxxxxxxxx] On Behalf Of Benoit Perrin
> Sent: Tuesday, April 08, 2014 4:15 AM
> To: tcf-dev@xxxxxxxxxxx
> Subject: [tcf-dev] Possible issue with symbols proxy
>
> Hi,
>
> I think that I found an issue with the symbols proxy (C code), but as I am not
> sure to understand completely the code, I prefer to send an email first than to
> create a bugzilla.
>
> My system has three contexts:
>
> P2 (process, symbol context)
> |_ P2.1 (thread)
> |_ P2.2 (thread)
>
> The code searches a symbol by address, and between the command sent and the
> reply received, a runcontrol context is removed.
>
> <--- C 129 Symbols findByAddr "P2.1" 1628750159
> <--- E None RunControl contextRemoved ["P2.2"]
> ---> R 129 None "@S3.73.BA634B.533E91BA.13CC.0.0.-1.0.0.0.P2"
>
>   From the symbols proxy code:
>
> find_symbol_by_addr() links the associated pending cache to the 'flush_rc'
> linked list, with an update_policy set to UPDATE_ON_EXE_STATE_CHANGES.
>
> When the context P2.2 is removed, the listener event_context_exited() is called.
> In that case, cached data associated with the context P2.2 for all policies
> would be flushed ("flush_syms(ctx, ~0)").
> The core routine to check if a cached data has to be flushed is check_policy(),
> which in the example will return '1' (mode is 0xffffffff, P2.1 and P2.2 share
> the same symbol context group P2). I don't think this is correct, as the cache
> is associated with P2.1 and not P2.2, so it should not be flushed.
> Moreover, the routine free_find_sym_cache() checks (asserts) that the data
> cached to be flushed is not a pending data.
>
> I am wondering if the check_policy() code is correct. Should it be instead:
>
>    static int check_policy(Context * ctx, int mode, Context * sym_grp, Context *
> sym_ctx, int policy) {
>        if ((mode & (1 << policy)) && sym_ctx == ctx) return 1;
>        if (mode & (1 << UPDATE_ON_MEMORY_MAP_CHANGES)) {
> -        if (context_get_group(sym_ctx, CONTEXT_GROUP_SYMBOLS) == sym_grp) return 1;
> +        if (context_get_group(sym_ctx, CONTEXT_GROUP_SYMBOLS) == ctx) return 1;
>        }
>        return 0;
>    }
>
>
> Regards,
>
> Benoit
>
> --
> Benoit Perrin, Senior Member of Technical Staff, Wind River
> direct +33 297.427.375
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--
Benoit Perrin, Senior Member of Technical Staff, Wind River
direct +33 297.427.375



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