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Date:      Thu, 25 Nov 2010 21:10:34 +0100
From:      Erik Cederstrand <erik@cederstrand.dk>
To:        Mark Johnston <markjdb@gmail.com>
Cc:        FreeBSD Hackers <hackers@FreeBSD.org>
Subject:   Re: Deterministic builds, part 2
Message-ID:  <0B04A57E-A325-4006-8A01-6C7F15584C2F@cederstrand.dk>
In-Reply-To: <20101125191727.GB1342@mark-laptop-bsd.mark-home>
References:  <93FA0AC7-704D-4EB4-A163-FDD8AC915630@cederstrand.dk> <20101125191727.GB1342@mark-laptop-bsd.mark-home>

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Den 25/11/2010 kl. 20.17 skrev Mark Johnston:

> On Thu, Nov 25, 2010 at 01:08:58PM +0100, Erik Cederstrand wrote:
>> Kernel modules:
>> ----------------------
>> In the ELF section .gnu-debuglink, there is a link to the =
corresponding *.ko.symbols file. It seems to be an inode or such rather =
than a file path since nothing shows up in strings(1). I have commented =
out "makeoptions DEBUG=3D-g" in the GENERIC kernel conf file which I am =
testing now, but I'd like to know what is actually going on.
>=20
> The .gnu_debuglink segment contains the name of the debug symbols file
> (i.e. not a full path or an inode number). I'm not sure why it doesn't
> show up with strings(1), but you can see it with a hex editor.
>=20
> When gdb loads an object file with a gnu_debuglink segment, it looks =
in
> a few pre-defined locations for the corresponding symbols file. The =
gdb
> docs explain it pretty well:
>=20
> http://sourceware.org/gdb/onlinedocs/gdb/Separate-Debug-Files.html

Thanks. I was explained in private email that I should be using "strings =
-a" which indeed turns up the filename. The checksum mismatch actually =
occurs because the section also contains a CRC of the symbols file, =
which means the symbols files aren't identical. I'll investigate that =
separately.

Erik=

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