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From: Alexander Monakov <amonakov@ispras.ru>
To: Stefan Seefeld <stefan_seefeld@mentor.com>
Cc: lttng-dev@lists.lttng.org
Subject: Re: [PATCH lttng-ust] Add trace support for calloc and realloc.
Date: Thu, 1 Aug 2013 21:57:28 +0400	[thread overview]
Message-ID: <CABtfrpDg_NOi+yP5GABmjBv6G9Zj+rvTwc1OdQ1s_9DM7uzeZg__37845.4732629054$1375379911$gmane$org@mail.gmail.com> (raw)
In-Reply-To: <51FA9AD8.4010502@mentor.com>

On Thu, Aug 1, 2013 at 9:28 PM, Stefan Seefeld
<stefan_seefeld@mentor.com> wrote:
> I don't think any of this works. The ultimate problem is the one Jérémie
> reported initially: dlsym will eventually call free() on the memory
> calloc() returned, so my calloc fallback needs to return something that
> can actually be freed.

I pointed out how free() will be safe specifically:

>> dlsym stores pointer to calloc'ed buffer, overwriting the pointer to mmap'ed
>> buffer, completing initialization for the second time and making the
>> subsequent free() safe.

Besides, you're intercepting free() in your LD_PRELOAD module as well,
so you can just catch attempts to free your mmap'ed buffers there and
munmap them safely.

Alexander

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  parent reply	other threads:[~2013-08-01 17:57 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <51F3585E.20705@mentor.com>
2013-07-29 23:19 ` [PATCH lttng-ust] Add trace support for calloc and realloc Jérémie Galarneau
     [not found] ` <CA+jJMxtn-DsBjzunLNE3_7KS4RCqAFLJfPL7fVkH3z62r0jPxw@mail.gmail.com>
2013-07-30 21:12   ` Stefan Seefeld
     [not found]   ` <51F82C45.6020502@mentor.com>
2013-07-31  2:14     ` Jérémie Galarneau
     [not found]     ` <CA+jJMxtMH5Ajgoszg8pO8dq-KsrTg9NwS2YcYOz=FbLr0ijaEQ@mail.gmail.com>
2013-08-01 16:26       ` Alexander Monakov
     [not found]       ` <alpine.LNX.2.00.1308012013380.9574@monopod.intra.ispras.ru>
2013-08-01 16:32         ` Stefan Seefeld
     [not found]         ` <51FA8DAE.3070409@mentor.com>
2013-08-01 17:08           ` Alexander Monakov
     [not found]           ` <alpine.LNX.2.00.1308012045570.9574@monopod.intra.ispras.ru>
2013-08-01 17:19             ` Alexander Monakov
     [not found]             ` <alpine.LNX.2.00.1308012115300.9574@monopod.intra.ispras.ru>
2013-08-01 17:28               ` Stefan Seefeld
     [not found]               ` <51FA9AD8.4010502@mentor.com>
2013-08-01 17:57                 ` Alexander Monakov [this message]
     [not found]                 ` <CABtfrpDg_NOi+yP5GABmjBv6G9Zj+rvTwc1OdQ1s_9DM7uzeZg@mail.gmail.com>
2013-08-03  1:18                   ` Mathieu Desnoyers
     [not found]                   ` <20130803011841.GE9033@Krystal>
2013-08-05 14:57                     ` Stefan Seefeld
2013-08-05 15:29                     ` Stefan Seefeld
     [not found]                     ` <51FFBD46.5030105@mentor.com>
2013-08-07  1:42                       ` Mathieu Desnoyers
     [not found]                       ` <20130807014241.GH19407@Krystal>
2013-08-07 13:37                         ` Stefan Seefeld
     [not found]                         ` <52024D88.8090409@seefeld.name>
2013-08-07 13:57                           ` Mathieu Desnoyers
     [not found]                           ` <20130807135757.GA32387@Krystal>
2013-08-07 14:01                             ` Stefan Seefeld
     [not found]                     ` <51FFC4DB.7080905@mentor.com>
2013-08-07 14:47                       ` Stefan Seefeld
     [not found]                       ` <52025E03.7090201@mentor.com>
2013-08-07 15:50                         ` Mathieu Desnoyers
     [not found]                         ` <20130807155057.GB1035@Krystal>
2013-08-07 15:56                           ` Stefan Seefeld
2013-08-07 17:07                           ` Stefan Seefeld
     [not found]                           ` <52027EE6.60704@mentor.com>
2013-08-07 18:35                             ` Mathieu Desnoyers
2013-07-27  5:19 Stefan Seefeld

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