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Re: RFE: dl_iterate_phdr, r_debug.r_brk usability for introspection
- From: Rich Felker <dalias at libc dot org>
- To: John Reiser <jreiser at bitwagon dot com>
- Cc: libc-alpha at sourceware dot org
- Date: Tue, 15 Sep 2015 10:09:29 -0400
- Subject: Re: RFE: dl_iterate_phdr, r_debug.r_brk usability for introspection
- Authentication-results: sourceware.org; auth=none
- References: <55F5A822 dot 1050609 at bitwagon dot com>
On Sun, Sep 13, 2015 at 09:45:22AM -0700, John Reiser wrote:
> Counting and reporting the number of calls to dlopen and dlclose
> would enhance the usability of dl_iterate_phdr. A related change
> to r_debug.r_brk would make life easier for live introspection.
Can you offer some intended usage cases? I'm not seeing how this
"enhances the usability".
> For dl_iterate_phdr: count the number of calls to dlopen and dlclose.
> Report the counts to the callback function as new members of
> struct dl_phdr_info. Also tell the number of iterations remaining:
> unsigned dlpi_n_dlopen; /* # calls in this process */
> unsigned dlpi_n_dlclose; /* # calls in this process */
> unsigned dlpi_n_more; /* # remaining link_map along .r_map */
>
> By remembering .dlpi_n_dlopen and .dlpi_n_dlclose from the previous
> invocation of dl_iterate_phdr, then the app can tell which kind of
> changes, or determine quickly that there have been no changes.
> The data member .dlpi_n_more enables effective planning for
> resources which depend on the number of link_map instances.
The type unsigned is way too small for this and subject to overflow.
Counters like this need to be at least 64-bit.
Rich