Linux: FPU control word not set when __fpu_control == _dl_fpu_control.

[Scott Bambrough]

Hi guys,

I've built a versioned glibc 2.1.3 on a NetWinder, and a kernel with a debug
printk on WFS (the instruction called when __setfpucw is called).  If I build
static and dynamic test executables (I was using fp-cmp-1.c from the gcc
testsuite), I only get a printk from WFS when the static executable is run.

If I look at sysdeps/unix/sysv/linux/init-first.c, around line 70, there is a
call to __setfpucw that should be executed.  If I look at the the generated .o
and .os files it is easy to see why it is failing.  It doesn't work when
dynamically linked because of the if statement included when compiling with PIC
enabled.

As far as I can tell __fpu_control is almost always equal to _dl_fpu_control. 
__fpu_control is defined and statically initialized in
sysdeps/generic/fpu_control.c.  It is initialized with _FPU_DEFAULT. 
_dl_fpu_control is defined in elf/rtld.c, and statically initialized with
_FPU_DEFAULT.  It is also dynamically initialized from _dl_sysdep_start in
sysdeps/generic/dl-sysdep.c.  The initialization is done if the flag AT_FPUCW is
in the the headers in the executable.  The value used is taken from the
executable as well.

This doesn't seem to be an ARM specific problem, but a Linux specific one.  Does
anyone else see the same thing on other platforms?

Scott


-- 
Scott Bambrough - Software Engineer
REBEL.COM    http://www.rebel.com
NetWinder    http://www.netwinder.org