PowerPC gcc drops incorrect code

[James Macfarlane <list1 at mcflan dot org>]

Hi

I'm new to this list so forgive me if there's an obvious answer to this. 
I've searched the archives and googled and found only vieled references 
to this problem.

I built gcc-3.4.3-glibc-2.3.2 for powerpc-8540-linux-gnu using 
crosstools 0.35 and I just tried 0.38 too.

I did the crosstool build with:

    TARGET=powerpc-8540-linux-gnu
    TARGET_CFLAGS="-O -mcpu=8540"
    GCC_EXTRA_CONFIG="--with-cpu=8540 --enable-cxx-flags=-mcpu=8540"
    GLIBC_EXTRA_CONFIG="--without-fp"

I built a kernel using my new shiny crosstool gcc and it worked great. I 
then built busybox and got "Illegal instruction" errors on doing an nfs 
mount.

Basically, the compiler will generate lswi and stswi (string word 
instructions) when compiling with the -Os (optimise for space) flag. 
These instructions are not supported on various powerpc platforms 
(including mine - an mpc8560 which uses the e500 core, like the 8540). 
You can stop gcc doing this by issuing the -mno-string flag. However, 
the manpage for gcc clearly states that for powerpc architectures, this 
flag is set by default (i.e. -mstring is off). So, you shouldn't have 
to do this. Setting -mno-string manually in target build scripts works, 
but is a gross hack and a pain in the back side when building a whole 
bunch of stuff. 

My question is, has anyone encountered this before, and do they know if 
it's a gcc bug or a crosstool bug, or just a dumb-ass mistake on my 
part ?

I couldn't find any relevant patches to fix this, but that might just be 
because I haven't yet looked hard enough.

I think the key to this lies in gcc-3.4.3/gcc/configs/rs6000/rs6000.[ch] 
but I'd be interested if anyone can shed any light on this before I 
delve too much deeper.

Cheers,
James.
--
James Macfarlane

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