From: Richard Gorton <rcgorton@cognitive-electronics.com>
To: musl@lists.openwall.com
Subject: magic constants in some startup code
Date: Fri, 31 Oct 2014 09:31:37 -0400 [thread overview]
Message-ID: <45BFC4C3-FA51-49B5-8C58-1C1FC075BD28@cognitive-electronics.com> (raw)
We're using musl for our processor architecture; as part of doing the bring-up work, I need to fully understand process launching and thread creation.
As I'm reading through the source code, I see (more than one) 'magic' constants that I do not fully understand (musl 1.1.5), and would like to know 'how and why':
src/env/__init_tls.c:
static long long builtin_tls[(sizeof(struct pthread) + 64)/sizeof(long long)];
I'm guessing that 64 is an arbitrary 'small' default amount of TLS? Or is this to hold another specific bit of data?
----
src/env/__stack_chk_fail.c
else __stack_chk_guard = (uintptr_t)&__stack_chk_guard * 1103515245;
the number equates to 0x41c64e6d.
Called from __init_libc as:
__init_ssp((void *)aux[AT_RANDOM]);
The kernel is putting a random number into aux[AT_RANDOM] at process initialization.
Why not just put a predictable arbitrary number into __stack_chk_guard?
Regards,
Richard
rcgorton@cog-e.com
next reply other threads:[~2014-10-31 13:31 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-10-31 13:31 Richard Gorton [this message]
2014-10-31 14:18 ` Rich Felker
2014-10-31 14:31 ` Richard Gorton
2014-10-31 16:09 ` Rich Felker
2014-10-31 20:19 ` Andy Lutomirski
2014-10-31 21:05 ` Rich Felker
2014-10-31 21:29 ` Andy Lutomirski
2014-10-31 21:39 ` Rich Felker
2014-10-31 22:27 ` Andy Lutomirski
2014-10-31 23:14 ` Rich Felker
2014-11-02 17:17 ` Szabolcs Nagy
2014-11-02 19:10 ` Andy Lutomirski
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=45BFC4C3-FA51-49B5-8C58-1C1FC075BD28@cognitive-electronics.com \
--to=rcgorton@cognitive-electronics.com \
--cc=musl@lists.openwall.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.
Code repositories for project(s) associated with this public inbox
https://git.vuxu.org/mirror/musl/
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 NNTP newsgroup(s).