I want mregparm!

[dete]

I know that adding -mregparm=3 to my CFLAGS will break compatibility with any binary libraries/applications. But I also know that I'm gonna compile everything I put on this machine, and regparm is cool.

However!

When I'm trying to bootstrap, I'm running into the problem that the config scripts invoke the compiler with my CFLAGS, and the bootstrap CD is built without regparm... things get haywire.

Specifically, when glibc is being built, it compiles lots of little programs to determine things -- for example, the size of a long double. However, it checks the status code on those programs and the return codes are bogus if I use regparm. (On my machine, the status for every tool compiled with regparm is 80.)

So, has anyone ever gotten mregparm=3 to work globally in CFLAGS.

If not, does anyone have any tips? Seems to me the best option would be if there was some way of specifying flags used for building, but ignored for config, but that seems unlikely. Any other ideas? Would it be possible to build a bootstrap CD with -mregparm=3, or will I run into the same problem? Is there some way I can tell every little config tool to use exit(code)? instead of return code;? (Would that even help?)

Any tips and discussion are appreciated!

[racoontje]

Either you make a custom CD which fixes the faulty file(s), or you pick the easy way out, wait 'till the minimum install is done, and emerge -e world when you're done (with the new CFLAGS, of course)

[dete]

I thought about emerge -e world, but isn't that going to run into exactly the same problem? The main system (which is calling the config programs) is going to be incompatible.

About building the CD: Are there docs somewhere on how to build my own?

It occurred to me that I'm for all intents and purposes doing a cross-compile; generating code that doesn't work on the host that's doing the building. Is there any Gentoo support for this more general case?

[Eduard Munteanu]

It's almost 2007 and this problem is still here. Where am I supposed to get a regparm-built glibc to bootstrap the toolchain? This is a chicken and egg problem AFAICS. Any ideas?

[nixnut]

Moved from Installing Gentoo to Unsupported Software.
DIY-cd's are not supported installation methods, so moved here.
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[irondog]

[Eduard Munteanu]

[Enlight]

Well this question doesn't interess me as much 'cause I'm now on amd64 (and when I run 32 bits apps, it's only for binary compability), but you need to understand that modifying ABI requires the same actions as cross-compiling, so you have to built a static toolchain, then start with glibc (IMHO)... unfortunately, I never figured out how to build a static toolchain with gentoo... Maybe I didn't looked deep enough into the toolchain eclass.

Still if you plan on modifying as far you system, go for malign-double and all flags that changes the abi in the x86_64 way, try also freg-struct-registers etc...

edit : about cflags control, souldn't add the abi cflags to ALLOWED_FLAGS be enough?

[irondog]

[Eduard Munteanu]

I understand. Thanks for pointing out the cross-compiler could work. I had just a theoretical interest in this matter (thought it could help in certain environments to have mregparm).

Yes, glibc contains inline asm, but I think it's only related to syscalls and such (correct me if I'm wrong, please). And userspace <-> kernelspace ABI is not affected by something like mregparm=3, there is a standard interface no matter how you build apps/kernel (probably that's why we have hardcoded asm here and there).

Anyway, I personally don't recommend this flag unless the risks/benefits balance strongly favors it (which doesn't happen usually), so we're on the same side.

[irondog]