Fresh installed Freebsd 9 don't boot from hd

[Dennis Koegel]

On Fri, Oct 21, 2011 at 04:33:38PM -0400, John Baldwin wrote:
> Working offline with Dennis, we found that changing the CFLAGS in 
> sys/boot/i386/gptboot/Makefile from "-O1" to "-Os -mrtd" (partially reverting 
> an earlier commit) fixed gptboot.  The next test for someone to do would be to 
> try just adding "-mrtd" and leaving "-O1" as-is to see if that fixes it.

More test results:

gcc -Os -fno-guess-branch-probability -fomit-frame-pointer -fno-unit-at-a-time \
	-mno-align-long-strings -mrtd [from before r225530]: Boots OK
gcc -Os -mrtd: Boots OK
gcc -O1 -mrtd: Fails
gcc -O1: Fails
gcc -O0: Fails
gcc -Os: Boots OK

clang -O1: Fails
clang -Os: Fails
clang -Oz: Fails

I've put some printf()s into gpt{,boot}.c to trace where the reboot is
triggered. It appears to be in drvsize() (called from gptread()). OTOH
the debug output may have changed where the problem occurs, I don't
know about that.

With 9.0R drawing near, CFLAGS should be s/-O1/-Os/, until we can figure
out what happens. But as for why gcc's magic -Os is required and clang's
output doesn't work at all, I'm clueless.

- D.