building world with debugging symbols [broken?]

Ted Faber faber at
Tue Jun 22 21:07:31 UTC 2010

On Tue, Jun 22, 2010 at 04:39:17PM -0400, Ryan Stone wrote:
> I saw similar behaviour a couple of years ago when I switched from
> using gcc 4.0.2 to gcc 4.3.0 to compile some out-of-tree KLD modules.
> The problem ended up being a change in the linker script used by GNU
> ld for linking kernel modules.  It used to always put some magic
> symbols used by the linker to implement things like sysinits into the
> module.  It was changed to only provide those symbols, which
> apparently means that the linker would discard those symbols if
> nothing referenced them(and nothing did reference them).  I had to
> work around it by adding the following to my link line:
> -u __start_set_sysinit_set -u __start_set_sysuninit_set \
> -u __start_set_sysctl_set -u __start_set_modmetadata_set \
> -u __stop_set_sysinit_set -u __stop_set_sysuninit_set \
> -u __stop_set_sysctl_set -u __stop_set_modmetadata_set


I added those lines to the LDFLAGS in Makefile.kmod in the cuse4bsd port
made the module and the result loads and creates the /dev/cuse file.

Here's a diff relative to
/usr/ports/multimedia/cuse4bsd-kmod/work/cuse4bsd-kmod-0.1.11 just so
it's clear what I did.

--- Makefile.kmod.orig  2010-02-11 03:28:02.000000000 -0800
+++ Makefile.kmod       2010-06-22 14:02:52.000000000 -0700
@@ -30,4 +30,10 @@
 KMOD=  cuse4bsd
 SRCS=  cuse4bsd_kmod.c device_if.h bus_if.h vnode_if.h
+LDFLAGS += -u __start_set_sysinit_set -u __start_set_sysuninit_set \
+ -u __start_set_sysctl_set -u __start_set_modmetadata_set \
+ -u __stop_set_sysinit_set -u __stop_set_sysuninit_set \
+ -u __stop_set_sysctl_set -u __stop_set_modmetadata_set
 .include <>

Running nm -o on the two modules, the difference seems to be that the -u
results in some additional absolute symbols being defined:

Bad module:
$ nm -o /boot/modules/cuse4bsd.ko| grep sys
/boot/modules/cuse4bsd.ko:0000275c r
/boot/modules/cuse4bsd.ko:00002758 r __set_sysuninit_set_sym_cuse_kern_uninit_sys_uninit
/boot/modules/cuse4bsd.ko:00003194 d cuse_kern_init_sys_init
/boot/modules/cuse4bsd.ko:00003184 d cuse_kern_uninit_sys_uninit

Good module:

$ nm -o ./cuse4bsd.ko  | grep sys
./cuse4bsd.ko:000028cc r __set_sysinit_set_sym_cuse_kern_init_sys_init
./cuse4bsd.ko:000028c8 r __set_sysuninit_set_sym_cuse_kern_uninit_sys_uninit
./cuse4bsd.ko:         U __start_set_sysctl_set
./cuse4bsd.ko:000028cc A __start_set_sysinit_set
./cuse4bsd.ko:000028c8 A __start_set_sysuninit_set
./cuse4bsd.ko:         U __stop_set_sysctl_set
./cuse4bsd.ko:000028d0 A __stop_set_sysinit_set
./cuse4bsd.ko:000028cc A __stop_set_sysuninit_set
./cuse4bsd.ko:00003194 d cuse_kern_init_sys_init
./cuse4bsd.ko:00003184 d cuse_kern_uninit_sys_uninit

Ted Faber           PGP:
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