From: "Jan Beulich" <JBeulich@novell.com>
To: "Jakub Jelinek" <jakub@redhat.com>,"Jan Hubicka" <hubicka@ucw.cz>
Cc: "GCC Development" <gcc@gcc.gnu.org>,
"H.J. Lu" <hjl.tools@gmail.com>,<x32-abi@googlegroups.com>,
"Binutils" <binutils@sourceware.org>,
"GNU C Library" <libc-alpha@sourceware.org>,
"H. Peter Anvin" <hpa@zytor.com>
Subject: Re: x32 psABI draft version 0.2
Date: Fri, 18 Feb 2011 08:49:00 -0000 [thread overview]
Message-ID: <4D5E40D80200007800032A0B@vpn.id2.novell.com> (raw)
In-Reply-To: <20110217230727.GK30899@tyan-ft48-01.lab.bos.redhat.com>
>>> On 18.02.11 at 00:07, Jakub Jelinek <jakub@redhat.com> wrote:
> So one way to cut down the size of .rela.dyn section would be a relocation
> like
> R_X86_64_RELATIVE_BLOCK where applying such a relocation with r_offset O and
> r_addend N would be:
> uint64_t *ptr = O;
> for (i = 0; i < N; i++)
> ptr[i] += bias;
> Then e.g.
> 0000003ec6d86008 0000000000000008 R_X86_64_RELATIVE
> 0000003ec5aef3f3
> 0000003ec6d86010 0000000000000008 R_X86_64_RELATIVE
> 0000003ec5af92f6
> 0000003ec6d86018 0000000000000008 R_X86_64_RELATIVE
> 0000003ec5b06d17
> 0000003ec6d86020 0000000000000008 R_X86_64_RELATIVE
> 0000003ec5b1dc5f
> 0000003ec6d86028 0000000000000008 R_X86_64_RELATIVE
> 0000003ec5b1edaf
> 0000003ec6d86030 0000000000000008 R_X86_64_RELATIVE
> 0000003ec5b27358
> 0000003ec6d86038 0000000000000008 R_X86_64_RELATIVE
> 0000003ec5b30f9f
> 0000003ec6d86040 0000000000000008 R_X86_64_RELATIVE
> 0000003ec5b3317d
> 0000003ec6d86048 0000000000000008 R_X86_64_RELATIVE
> 0000003ec5b34479
> could be represented as:
> 0000003ec6d86008 00000000000000MN R_X86_64_RELATIVE_BLOCK
> 0000000000000009
> I see many hundreds of consecutive R_X86_64_RELATIVE relocs in libxul.so,
> though
> of course it would need much better analysis over larger body of code.
>
> In most programs if the library is prelinked all relative relocs are skipped
> and .rela.dyn for them doesn't need to be even paged in, but Mozilla is
> quite
> special in that it one of the most common security relevant packages and
> thus
> wants randomization, but is linked against huge libraries, so the question
> is
> if Mozilla is the right candidate to drive our decisions on.
>
> Another alternative to compress relative relocations would be an indirect
> relative relocation, which would give you in r_offset address of a block of
> addresses
> and r_addend the size of that block, and the block would just contain
> offsets
> on which words need to be += bias. Then, instead of changing RELA to REL to
> save 8 bytes from 24 you'd save 16 bytes from those 24 (well, for x32 half
> of that).
For relocations where the relocated field is large enough, considering
chained relocations (as seen in NetWare NLMs) would also be a
possibility, i.e. r_offset specifies just the first relocation that all need
the same addend (and eventual other properties), and the relocated
field holds the r_offset of the next field to be relocated.
Jan
next prev parent reply other threads:[~2011-02-18 8:49 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-02-16 19:22 H.J. Lu
2011-02-16 20:04 ` H. Peter Anvin
2011-02-16 20:29 ` Roland McGrath
2011-02-16 20:35 ` Chris Metcalf
2011-02-16 20:39 ` Andrew Pinski
2011-02-16 20:46 ` H.J. Lu
2011-02-16 22:13 ` Chris Metcalf
2011-02-17 8:35 ` Jan Beulich
2011-02-17 12:14 ` H.J. Lu
2011-02-17 16:14 ` John Reiser
2011-02-17 17:59 ` Jakub Jelinek
2011-02-17 14:29 ` Jakub Jelinek
2011-02-17 15:22 ` Jan Hubicka
2011-02-17 15:30 ` H.J. Lu
2011-02-17 15:45 ` Jan Hubicka
2011-02-17 15:49 ` H.J. Lu
2011-02-17 16:10 ` Jan Beulich
2011-02-17 17:59 ` H.J. Lu
2011-02-18 8:10 ` Jan Beulich
2011-02-18 17:53 ` H.J. Lu
2011-02-18 20:32 ` Jan Hubicka
2011-02-21 8:04 ` Jan Beulich
2011-02-17 18:07 ` Jakub Jelinek
2011-02-17 19:56 ` H. Peter Anvin
2011-02-17 22:50 ` Jan Hubicka
2011-02-17 23:00 ` H. Peter Anvin
2011-02-17 23:07 ` Jakub Jelinek
2011-02-18 8:49 ` Jan Beulich [this message]
2011-02-17 18:14 ` Joseph S. Myers
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