Re: [PATCH v2 1/5] powerpc/kbuild: set default generic machine type for 32-bit compile

On Thu, May 10, 2018 at 11:24:40PM +1000, Nicholas Piggin wrote:

On Thu, 10 May 2018 08:10:03 -0500
Segher Boessenkool [off-list ref] wrote:

quoted

On Thu, May 10, 2018 at 03:16:55PM +1000, Nicholas Piggin wrote:

quoted

The 64-bit toolchain uses the wrong ISA variant for compiling 32-bit
kernels, eve with -m32. Set -mcpu=powerpc which is the generic 32-bit
powerpc machine type and scheduling model. 32-bit platforms and CPUs
can override this with -mcpu= options that come later on the command
line.

This fixes a lot of build failures due to incompatible assembly when
compiling 32-bit kernel with 64-bit toolchain.  

So what ISA is set for gas without this patch?  With what GCC version?

I'm not sure, how do I find that out?

gcc --version
gcc -v <rest of command>, look at the command line options passed to as
make something.s, look at what .machine is set (if any).

quoted

And, why is that wrong?

Some 32-bit platforms and CPU types do not provide -mcpu, so I assume
for 32-bit toolchains that must result in the "powerpc" machine. With

It results in whatever is the default for that toolchain.  Depends on
many things.

64-bit toolchains 

arch/powerpc/mm/hash_low_32.S:353: Error: missing operand

Which is,

        tlbie   r4

Is that v2.06?

The original ISA did not have the L field, 2.xx does, for any xx even I think.


Segher