From: Szabolcs Nagy <szabolcs.nagy@arm.com>
To: Roland McGrath <roland@hack.frob.com>,
Renlin Li <renlin.li@foss.arm.com>
Cc: <nd@arm.com>, <libc-alpha@sourceware.org>,
Marcus Shawcroft <Marcus.Shawcroft@arm.com>,
Richard Earnshaw <Richard.Earnshaw@arm.com>
Subject: Re: [GLIBC][AARCH64]Rewrite elf_machine_load_address using _DYNAMIC symbol
Date: Mon, 07 Nov 2016 15:15:00 -0000 [thread overview]
Message-ID: <58209A8B.5030702@arm.com> (raw)
In-Reply-To: <20161104212440.A23F42C3AD8@topped-with-meat.com>
On 04/11/16 21:24, Roland McGrath wrote:
> On many or perhaps all machines, elf_machine_load_address could now be
> implemented purely in C by using a link-time trick.
>
> In C, just:
>
> static inline ElfW(Addr) __attribute__ ((unused))
> elf_machine_load_address (void)
> {
> extern const char _BASE[] __attribute__ ((visibility ("hidden")));
> return (ElfW(Addr)) _BASE;
> }
>
> Then add a trivial input linker script to the ld.so link:
>
> PROVIDE_HIDDEN(_BASE = 0);
>
> I know this works for x86_64 and aarch64, and does not require a load.
> (On x86_64 it's a single lea; on aarch64 it's a single adr+add pair.)
>
this is less maintenance work, because code can be shared,
but it is not a portable solution: it relies on linker
scripts and on the compiler not doing anything silly.
i think asm is preferable, unless we know that all
supported linkers handle this on all targets.
next prev parent reply other threads:[~2016-11-07 15:15 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-11-04 9:42 Renlin Li
2016-11-04 21:24 ` Roland McGrath
2016-11-07 15:15 ` Szabolcs Nagy [this message]
2016-11-07 15:23 ` Szabolcs Nagy
2016-11-07 15:52 ` Szabolcs Nagy
2016-11-09 19:06 ` Maciej W. Rozycki
2016-11-08 21:28 ` Roland McGrath
2016-11-09 14:48 ` Szabolcs Nagy
2016-11-09 22:02 ` Roland McGrath
2017-10-17 15:41 ` Szabolcs Nagy
2017-10-17 16:28 ` Szabolcs Nagy
2017-10-18 10:32 ` Renlin Li
2017-10-18 16:12 ` Szabolcs Nagy
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=58209A8B.5030702@arm.com \
--to=szabolcs.nagy@arm.com \
--cc=Marcus.Shawcroft@arm.com \
--cc=Richard.Earnshaw@arm.com \
--cc=libc-alpha@sourceware.org \
--cc=nd@arm.com \
--cc=renlin.li@foss.arm.com \
--cc=roland@hack.frob.com \
/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).