Re:

On Mon, 2021-12-27 at 22:09 -0500, Alain Toussaint wrote:
> 
> 
> Envoyé de mon iPad
> 
> > Le 27 déc. 2021 à 21:34, Ken Moffat
> > <[email protected]> a écrit :
> > 
> > On Mon, Dec 27, 2021 at 07:58:07PM -0500, Alain Toussaint wrote:
> > > Hello,
> > > 
> > > I'm doing a new build tonight on my main computer using alfs and while
> > > undergoing the procedure to build a number of BLFS applications, I found
> > > out it was possible to put in my set of C(XX)FLAGS. Given the opportunity,
> > > I'd like to know if it would be possible to build a no-multilib version of
> > > LFS+BLFS and putting in the needed -mx32 flags to build all the userspace
> > > component and applications for an old and slow Sandy Bridge laptop to give
> > > the thing a new lease on life?
> > > 
> > > Many thanks,
> > > Alain
> > 
> > No idea about setting the flags, but do you mean -mx32 (an obscure
> > variant, ISTR intel came up with it for possible telecomms
> > equipment) or -m32 (regular i686) ?  If you do mean -mx32, and can
> > set the flags, you probably want to look at gentoo: from memory one
> > of their devs was keen on -mx32, but when I last looked (many years
> > ago) it needed a lot of patching.
> > 
> > ĸen
> 
> I do mean -mx32, the variant which used all the registers from x64 but address
> pointers of 32 bits which indeed needed lot of patching. Not anymore because a
> few distros (cough…gentoo among others) provide basic userspaces with these
> particular features. The 32 bit addressing feature cut processor cache
> (instructions cache namely, not data cache) utilisation in half, thus the
> performance increase and the expanded register set compared to i686 also help
> quite a bit.
> 
> Finally, each userspace apps get its own 4GB segment of memory. Just about
> perfect for a laptop used for web browsing, email and ssh to the big large box
> currently compiling in my office (Ryzen, 64GB, 1.5TB of nvme sticks…)

In jhalfs (that is, the lfs build part), you can set the flags in the
"optimization" module. It's a little complicated, because the authors wanted to
be able to disable optimization for specific packages. You have to copy one of
the files in optimize/opt_config.d to a new file (for example O2pipe to mx32,
but have a look at other files to see different techniques that can be used),
set the flags you want (changing their names too: CFLAGS_O2pipe becomes
CFLAGS_mx32 for example), then edit optimize/opt_config so that DEF_OPT_MODE be
mx32. Then use the optimize/opt_override to set different flags for some
packages (if needed), or disable completely optimization (including MAKEFLAGS)
using the BLACKLIST variable in optimize/opt_config.

In blfs tools, this is somewhat simpler...

Pierre

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