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From: Florian Weimer <fweimer@redhat.com>
To: Rich Felker <dalias@libc.org>
Cc: Yehuda Yitchak <yehuda80@gmail.com>,  musl@lists.openwall.com
Subject: Re: [musl] Accessing Thread-Local-Storage in GDB
Date: Thu, 10 Feb 2022 12:23:31 +0100	[thread overview]
Message-ID: <87a6ezx8wc.fsf@oldenburg.str.redhat.com> (raw)
In-Reply-To: <20220209223155.GD7074@brightrain.aerifal.cx> (Rich Felker's message of "Wed, 9 Feb 2022 17:31:55 -0500")

* Rich Felker:

> Indeed, I was just offering a quick workaround that might help, not
> suggesting gdb should do that. __tls_get_addr can be used for
> non-dynamic symbols with information already available to the
> debugger. For core files you could probably simulate execution and
> abort if anything is reached that would need to change process state
> (lazy allocation) although that doesn't happen with musl anyway. But I
> wonder if the core file even records the x86 segment information
> needed to preserve thread pointer and simulate the %fs/%gs based
> loads on x86[_64]..?

The register is available as $fs_base on x86-64:

(gdb) print (void *)$fs_base
$1 = (void *) 0x7f2d12981740
(gdb) print *(void **)$fs_base
$2 = (void *) 0x7f2d12981740

It probably does not work on i386 (even as $gs_base).  I do not think it
depends on FSGSBASE support in the kernel, but maybe I'm mistaken.  I
think I looked at this three years ago and couldn't make it work.

Thanks,
Florian


  reply	other threads:[~2022-02-10 11:23 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-02-09  7:32 Yehuda Yitchak
2022-02-09 18:33 ` Rich Felker
2022-02-09 20:44   ` Florian Weimer
2022-02-09 22:31     ` Rich Felker
2022-02-10 11:23       ` Florian Weimer [this message]
2022-02-10 18:05         ` Yehuda Yitchak
2022-02-10 21:32           ` Rich Felker

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