Re: init fails w/ new build of gcc & glibc

At 05:22 PM 8/17/2001 -0500, Mark Hatle wrote:

quoted

Mark,

You mentioned these two exclusive ABIs a couple days ago. If you want to compile the
toolchain and the kernel correctly to insure run-time compatibility (in my case for 8xx),
would you do this

for kernel fp emulation
compile kernel with CONFIG_MATH_EMULATION=y, (do you use -msoft-float while compiling
kernel?)
then compile the toolchain without -msoft-float

Use the kernel parameters as they stand, I wouldn't mess with them....
(floating point is not supposed to happen in the kernel anyway, and when
it does it's almost always assembly that is trapped anyway.)

quoted

or

for soft-floating point - no kernel emulation
compile kernel CONFIG_MATH_EMULATION is not set (do you use -msoft-float while compiling kernel?)
then compile the toolchain with -msoft-float

Basically.. One thing to keep in mind on the 8xx (due to cache line
size) it'll never truely be compatable with the rest of the PPC world.
But on a processor like the 405 it "can be" compatable using the
CONFIG_MATH_EMULATION.  The catch is that you have a lot more overhead
doing emulation.... (The emulation itself is pretty fast, certainly no
slower then the software code invoked in -msoft-float..)  However, you
have much more context switching over head and possible cache
invalidation.  Also, your software could be using floating point
registers w/o you expliciting using float's or double's due to gcc
optimizations to argument passing.  All in all you will have a penalty
for using hard floating point on a soft-floating point architecture.

This is the reason that MontaVista has chosen to go the route of
soft-float...

To summarize for me (and others), "leave kernel parameters as they stand" means

CONFIG_MATH_EMULATION=y and compile with -msoft-float

"MontaVista has chosen to go the route of soft-float..." means that MontaVista's tools are compiled with -msoft-float and --without-fp. I should compile my apps and toolchain (or use MV's) the same way.


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