From: Godmar Back <godmar@gmail.com>
To: William Tambe via Libc-help <libc-help@sourceware.org>
Subject: What are the option for overriding system calls GNU libc calls?
Date: Thu, 22 Sep 2022 08:31:27 -0400 [thread overview]
Message-ID: <CAB4+JYKdVW2WxzA=Pij_C1xbOHdxh4qj6=nnueNdJcHcAUZ+KA@mail.gmail.com> (raw)
[-- Attachment #1: Type: text/plain, Size: 1061 bytes --]
Hi,
I have a question. Say I wanted to override the `write()` system call in an
application so that when I compile and link it, my version of `write()` is
called by both the application program as well as by GNU libc, for
instance, from puts or printf. To what extent is this supported?
I'm aware of the following options:
- (a) link statically. In this case, if I provide a strong definition of
`write()`, the application will pick it up. GNU libc, otoh, uses
`__write()` Overriding `__write` with a strong definition works and gets
libc to call my __write.
- (b) link dynamically and use `LD_PRELOAD`. In this case, I can get the
application to call my `write`, but libc will continue to call `__write`; I
believe; I haven't tried if I can provide a __write and have libc pick up
on it since (I thought) that libc resolves these symbols internally or from
a dynamic library on its link chain.
In any event, my question is: is there a sanctioned or semi-sanctioned way
to override system calls for both the static and dynamic linking process?
- Godmar
next reply other threads:[~2022-09-22 12:31 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-09-22 12:31 Godmar Back [this message]
2022-09-26 11:57 ` Adhemerval Zanella Netto
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='CAB4+JYKdVW2WxzA=Pij_C1xbOHdxh4qj6=nnueNdJcHcAUZ+KA@mail.gmail.com' \
--to=godmar@gmail.com \
--cc=libc-help@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).