optimization issue about -O2 and -Os

[Jim Wilson]

Ebony Zhu wrote:
> build some applications such as U-Boot, Busybox..., with the -Os
> optimization, the apps can be built but cannot run (just halted, there
> were even no error messages). If I use -O2 switch then everything is OK.
> 
> According to manpage of GCC, -Os is based on -O2 switch and does some
> work to reduce the code size. What GCC did on earth with the -Os switch?

The -Os option is buggy.  You might want to report a bug into our 
bugzilla bug datase.  See
     http://gcc.gnu.org/bugs.html
for more info on reporting bugs.

Though the -Os option is based on the -O2 option, it is a different 
option, that generates different code, and has different bugs.
-- 
Jim Wilson, GNU Tools Support, http://www.SpecifixInc.com