From: Alan Modra <amodra@gmail.com>
To: Cary Coutant <ccoutant@gmail.com>
Cc: "H.J. Lu" <hjl.tools@gmail.com>, Michael Matz <matz@suse.de>,
Rich Felker <dalias@libc.org>,
Carlos O'Donell <carlos@redhat.com>,
Florian Weimer <fweimer@redhat.com>,
nsz@port70.net, Jan Beulich <JBeulich@suse.com>,
Binutils <binutils@sourceware.org>,
gnu-gabi@sourceware.org
Subject: Re: RFC: Add GNU_PROPERTY_NEED_PHDRS
Date: Mon, 01 Jan 2018 00:00:00 -0000 [thread overview]
Message-ID: <20181003075416.GD3179@bubble.grove.modra.org> (raw)
In-Reply-To: <CAJimCsHSBKqrMz_0bLeb7s0D-b18eOzr=5zs7rOFXUwJDeiB0g@mail.gmail.com>
On Tue, Oct 02, 2018 at 02:06:43PM -0700, Cary Coutant wrote:
> Even with no-separate-code, or with a read-only segment before the
> text, the inclusion of the program headers in the first PT_LOAD
> segment is merely a happy accident -- it's a side effect of way the
> linker rounds segment boundaries down and up to page boundaries, and
> depends entirely on the property that the first PT_LOAD segment falls
> within the first page of the executable file.
As Michael would say, it's a hack. ;-)
> > 3. Ld won't create a PT_LOAD segment just to hold phdrs.
>
> You seem to be breezing right past the idea of doing exactly this.
> Why? The scripting language already allows you to declare which
> segment should include FILEHDR and PHDRS. For -z separate-code, why
> not use a default linker script with something like the following?
>
> PHDRS
> {
> headers PT_PHDR PHDRS ;
> interp PT_INTERP ;
> header_seg PT_LOAD FILEHDR PHDRS ;
> text PT_LOAD ;
> data PT_LOAD ;
> dynamic PT_DYNAMIC ;
> }
The script idea is probably not practical in view of all the
variations of headers we'd need. PT_NOTE, PT_TLS, PT_GNU_EH_FRAME,
PT_GNU_STACK, PT_GNU_RELRO come to mind, some of which depend on
executable contents.
I do agree that ld should be modified to create a PT_LOAD just for
headers when needed, probably keyed off SIZEOF_HEADERS in a script.
> And, really, there's no denying that adding an otherwise-unnecessary
> note section -- just to get us back into the realm of "it works by
> happy accident" -- is a pure hack.
I don't particularly like the note section hack, but I can see why HJ
did it that way. Adding a note section no doubt avoids objcopy bugs
that would otherwise need to be fixed.
--
Alan Modra
Australia Development Lab, IBM
next prev parent reply other threads:[~2018-10-03 7:54 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-01-01 0:00 H.J. Lu
2018-01-01 0:00 ` Michael Matz
2018-01-01 0:00 ` H.J. Lu
2018-01-01 0:00 ` Michael Matz
2018-01-01 0:00 ` H.J. Lu
2018-01-01 0:00 ` Michael Matz
2018-01-01 0:00 ` H.J. Lu
2018-01-01 0:00 ` Michael Matz
2018-01-01 0:00 ` H.J. Lu
2018-01-01 0:00 ` Cary Coutant
2018-01-01 0:00 ` Alan Modra [this message]
2018-01-01 0:00 ` Cary Coutant
2018-01-01 0:00 ` Alan Modra
2018-01-01 0:00 ` Cary Coutant
2018-01-01 0:00 ` H.J. Lu
2018-01-01 0:00 ` Rich Felker
2018-01-01 0:00 ` H.J. Lu
2018-01-01 0:00 ` Alan Modra
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=20181003075416.GD3179@bubble.grove.modra.org \
--to=amodra@gmail.com \
--cc=JBeulich@suse.com \
--cc=binutils@sourceware.org \
--cc=carlos@redhat.com \
--cc=ccoutant@gmail.com \
--cc=dalias@libc.org \
--cc=fweimer@redhat.com \
--cc=gnu-gabi@sourceware.org \
--cc=hjl.tools@gmail.com \
--cc=matz@suse.de \
--cc=nsz@port70.net \
/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).