From: "H.J. Lu" <hjl.tools@gmail.com>
To: Cary Coutant <ccoutant@gmail.com>
Cc: Generic System V Application Binary Interface
<generic-abi@googlegroups.com>, Florian Weimer <fw@deneb.enyo.de>,
gnu-gabi@sourceware.org
Subject: Re: RFC: Audit external function called indirectly via GOT
Date: Mon, 01 Jan 2018 00:00:00 -0000 [thread overview]
Message-ID: <CAMe9rOrCb37F4YEm7nXRsiFWf+sqiJ1NR=sUiT_R-Uox2S-e8A@mail.gmail.com> (raw)
In-Reply-To: <CAJimCsEgxDTfZTZPA63-ozuGr_UG4hcqRKyyjAwp9+27DrFvpw@mail.gmail.com>
On Tue, Mar 27, 2018 at 6:39 PM, Cary Coutant <ccoutant@gmail.com> wrote:
> I haven't seen a response yet to the primary point I was trying to make:
>
>> My suggestion was that the GOT entry could be statically initialized
>> by the linker to point to the provisional PLT entry, rather than
>> forcing the dynamic loader to go through all this messy computation.
>> If auditing is not enabled, it would process the GLOB_DAT relocation
>> normally, and set the GOT entry to point to the actual function,
>> bypassing the provisional PLT and PLTGOT entries completely. If
>> auditing is enabled, it could simply ignore the GLOB_DAT relocation
>> (or, if the binary is PIE, it could process it as a RELATIVE
>> relocation), and the -fno-plt calls will end up jumping to the
>> provisional PLT entry.
>>
>> (This is already how we handle the PLTGOT entries: the linker
>> statically initializes the entries to point to part (b)* of the PLT
>> entry, while putting JUMP_SLOT relocations for those entries into the
>> JMPREL table.)
>>
>> I think if you do that, none of these extra dynamic table entries will
>> be needed, ...
Your scheme is very similar to mine. Both generate one GLOB_DAT
and one JUMP_SLOT relocation for the same function symbol. But
only one of them should be used at run-time. Your scheme may be
simpler when LD_AUDIT is used since you don't need to update GOT
slot. But you still need to decide if a GLOB_DAT relocation should be
skipped for LD_AUDIT.
> ... or this secondary point:
>
>> ... except for the IGNORE_JMPREL flag that indicates there are
>> no JMPREL slots other than those for the provisional PLT entries. How
>> useful is that flag? If the final program has even one external call
>> that was *not* compiled with -fno-plt, you won't be able to set it.
>> Would it be better to partition the JMPREL and PLT tables into
>> "regular" and "provisional" entries? That would take just a single new
>> DT_PROVISIONAL_JMPREL entry to tell the dynamic loader where the
>> JMPREL entries for the provisional PLT entries begin; it can ignore
>> everything past that point when auditing is turned off.
>
This sounds a good idea.. I will take a look.
--
H.J.
next prev parent reply other threads:[~2018-03-28 2:59 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-01-01 0:00 H.J. Lu
2018-01-01 0:00 ` Florian Weimer
2018-01-01 0:00 ` H.J. Lu
2018-01-01 0:00 ` Florian Weimer
2018-01-01 0:00 ` H.J. Lu
2018-01-01 0:00 ` Florian Weimer
2018-01-01 0:00 ` Florian Weimer
2018-01-01 0:00 ` Carlos O'Donell
2018-01-01 0:00 ` Florian Weimer
2018-01-01 0:00 ` Carlos O'Donell
2018-01-01 0:00 ` Cary Coutant
2018-01-01 0:00 ` H.J. Lu
2018-01-01 0:00 ` Cary Coutant
2018-01-01 0:00 ` H.J. Lu [this message]
2018-01-01 0:00 ` Cary Coutant
2018-01-01 0:00 ` H.J. Lu
2018-01-01 0:00 ` Carlos O'Donell
2018-01-01 0:00 ` Florian Weimer
2018-01-01 0:00 ` H.J. Lu
2018-01-01 0:00 ` Florian Weimer
2018-01-01 0:00 ` H.J. Lu
2018-01-01 0:00 ` H.J. Lu
2018-01-01 0:00 ` Cary Coutant
2018-01-01 0:00 ` Carlos O'Donell
2018-01-01 0:00 ` Cary Coutant
2018-01-01 0:00 ` Alan Modra
2018-01-01 0:00 ` H.J. Lu
2018-01-01 0:00 ` Alan Modra
2018-01-01 0:00 ` H.J. Lu
2018-01-01 0:00 ` H.J. Lu
2018-01-01 0:00 ` Cary Coutant
2018-01-01 0:00 ` Cary Coutant
2018-01-01 0:00 ` H.J. Lu
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to='CAMe9rOrCb37F4YEm7nXRsiFWf+sqiJ1NR=sUiT_R-Uox2S-e8A@mail.gmail.com' \
--to=hjl.tools@gmail.com \
--cc=ccoutant@gmail.com \
--cc=fw@deneb.enyo.de \
--cc=generic-abi@googlegroups.com \
--cc=gnu-gabi@sourceware.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).