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Subject: [Bug 207898] kernel linker behaves differently on amd64 vs. i386
Date: Sun, 13 Mar 2016 22:50:56 +0000
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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=3D207898

Jilles Tjoelker <jilles@FreeBSD.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jilles@FreeBSD.org

--- Comment #2 from Jilles Tjoelker <jilles@FreeBSD.org> ---
There is another MD aspect of the kernel linker: whether kernel modules are
object files (file says "ELF xx-bit yyy relocatable") or DSOs (file says "E=
LF
xx-bit yyy shared object"). Of the architectures you are looking at, i386 u=
ses
DSOs and amd64 uses object files.

Using object files may reduce overhead slightly but bypasses functionality =
that
may be useful. For example, DSOs have a symbol table for dynamic linking
separate from the one for debugging, while object files only have a single
symbol table. Although there is a flag for static (local) symbols, the kern=
el
linker ignores it and some code may have started abusing this ignoring.

Note that, although i386 kernel modules are DSOs, they are not PIC and do n=
ot
use a GOT and PLT. Therefore, there is no overhead from the DSO format while
running the code.

--=20
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