Building Pentium-M optimized system on Pentium4

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forbjok · Post by **forbjok** » Wed Dec 15, 2004 8:03 am

I'm planning to do a full system rebuild for my Pentium-M based Centrino laptop, and I'm wondering if it's possible to do the complete install process (bootstrap, emerge system, etc) on my Pentium4 desktop (hopefully soon to have 1.5GB RAM

) while optimizing for the Pentium-M architecture (gcc 3.4), make a tarball of the complete build, and extract it onto my laptop's gentoo partition (after reformatting it of course).

I know the system can be built on a different computer, as I did it once before on an Athlon Thunderbird 1.4 for a 486.
Works great, and it saved me a few years of compile time

That was done directly on an old HDD, using an USB-IDE adapter, though I can't think of any reason why it wouldn't work just as well with a tarball.

The main issue, however, is the architecture. Since I will be building with 'pentium-m' optimization, the build process will eventually start using the pentium-m optimized tools and compilers - normally, when building directly on the Pentium-M system, this is fine, but how will the Pentium4 handle it?
I imagine the pentium-m optimized executables will probably run on the Pentium4, but will the results be... how should I put this.. stable?

Will the system be built properly, just as it would directly on a Pentium-M system, or will I end up with a questionable half-corrupted build?

xbmodder · Post by **xbmodder** » Wed Dec 15, 2004 4:21 pm

it will work. p-m almost = p4

forbjok · Post by **forbjok** » Wed Dec 15, 2004 8:25 pm

xbmodder wrote:it will work. p-m almost = p4

Ok, thanks. I hope so

I'm gonna give it a try, maybe tomorrow.

racoontje · Post by **racoontje** » Wed Dec 15, 2004 9:38 pm

Almost? Yeah, like CND is almost USD :-/

P-M is a lot closer to P3 though.

mcdermottpa · Post by **mcdermottpa** » Sun Dec 19, 2004 7:21 am

racoontje wrote:Almost? Yeah, like CND is almost USD :-/

P-M is a lot closer to P3 though.

I second this. There are several good posts about comiling for pentium-m's. A quick read on the pentium-m arch will tell you that it is derived from the Pentium III line. You have to be using gcc 3.4 to compile with '-march=pentium-m' so as I understand it you would first have to upgrade gcc.

One post mentions doing a stage 1, bootstraping, compiling a small version of gcc 3.4, bootstaping again with that since the stage 1 still uses an older gcc, and doing the rest of the install.

Maybe someone who has actually acoplished this feat will post a reply? As soon as there is documented success somewhere I might just give it a try on my laptop.

forbjok · Post by **forbjok** » Fri Jan 07, 2005 10:13 pm

I finally got around to trying this a few days ago. I'm now typing from the laptop, running the new system compiled on my P4

Basically I did a full bootstrap w/ linux26-headers (emerged before bootstrap) and nptl enabled using the default GCC 3.3, then emerged GCC 3.4, gcc-config'ed and ran bootstrap again, now with -march=pentium-m instead of pentium4.

Then I did "emerge system" as usual, and the usual configuration (as according to the Gentoo Handbook - well, more or less anyway

)
I did also emerge grub, as I would need it later, but did not install it, as I did not want it to mess with the current bootloader on my P4.

Finally, I emerged xorg-x11, fluxbox, xmms, k3b, xine, vlc and various other X related programs, so the system would be as usable as possible immediately.

I tarred the entire contents of the partition I did the build on, and copied it over to the laptop using scp. Then I booted a Gentoo livecd, reformatted the partitions (after backuping some stuff), and after mounting the root partition on /mnt/gentoo, as during a normal install, I untarred the file from the P4 into /mnt/gentoo, and chrooted into it.

Then I configured /etc/fstab and reinstalled grub, and rebooted.
Seems to work fine so far

Basically, I had a new system running on my laptop in just a few minutes (the P4 was busy for a few days though), that would otherwise have left my laptop quite useless for days - the P4 was still perfectly usable while compiling as well

Hauser · Post by **Hauser** » Sat Jan 08, 2005 6:04 am

I did the same thing on my XP desktop, and the pentium-m system even runs on the XP machine, so I was able to finetune it before I moved it to my new notebook.

Jerem · Post by **Jerem** » Tue Jan 11, 2005 5:33 pm

Pentium M is NOT a pentium 4. Setting cflag "march=pentium-m" is not recommended AT ALL.

Set rather : CFLAG="-march=pentium-m" under GCC-3.4
and "-march=pentium3 -msse2" under GCC 3.3

The pentium M is a pentium 3 heavily modified to handle sse2 instruction set and it has also an improved branch prediction system(+20% success) and special instructions to save power.