Re: [RFC] Unable to use qemu-ppc to run 32-bit powerpc executables generated on gcc110 machine

[Pierre Muller]

Le 12/08/2022 à 06:16, Thomas Huth a écrit :
> On 11/08/2022 23.38, Pierre Muller wrote:
> >     I am using qemu to check code generated by Free Pascal compiler
> > for various CPUs.
> >
> >     Recently, this allowed me to find out that Free Pascal was generating
> > wrong instructions, leading to SIGBUS errors using qemu-mips.
> >     The same binaries worked without troubles on mips test machines,
> > probably because SIGBUS is handled directly inside the kernel.
> >
> >     Here I would like to report the problem I get when trying to run
> > powerpc executables using shared libs generated on gcc110 machine.
> >
> >     I copied over the needed libraries into a sys-root directory.
> >
> >     The problem is that the code crashes with a Illegal Instruction
> > after only a very few instructions:
> >
> > muller@gcc186:~/pas/check$ ~/sys-root/bin/qemu-ppc -cpu g2 -d in_asm -L
> > ~/sys-root/powerpc-linux ./twide1
> [...]
> > 0x3ffc1d60:  f00004d7  xxlxor   v0, v0, v0
> >
> > qemu: uncaught target signal 4 (Illegal instruction) - core dumped
> >
> > The problem is the the 'xxlxor' instruction is a VSX extension instruction.
> >
> >    There is apparently no cpu in the powerpc cpu list that enabled this
> > extension.
> > The output of cat /proc/cpuinfo on gcc110 gives that:
> > .....
> > processor       : 63
> > cpu             : POWER7 (architected), altivec supported
> > clock           : 3550.000000MHz
> > revision        : 2.1 (pvr 003f 0201)
> >
> > timebase        : 512000000
> > platform        : pSeries
> > model           : IBM,8231-E2B
> > machine         : CHRP IBM,8231-E2B
> >
> >     Is there a way to enable cpu features separately for ppc like is done for
> > x86_64?
> > Or would it be possible to define a new cpu inside qemu source that would match
> > the description above?
>
> So you are building on a POWER7 host and try to run the binaries on an
> emulated G2? That sounds weird. Why don't you use

  The g2 was just an example, I used a script to iterate
over all possible cpus (as listed by --cpu help),
but I always get a Illegal instruction on xllxor,
because none of the cpu in the least seems to enable VSX
extension.

>    qemu-ppc64 -cpu power7 ...

Because I am interested in testing 32-bit ELF binaries:

muller@gcc186:~/pas/check$ file ./twide1
./twide1: ELF 32-bit MSB executable, PowerPC or cisco 4500, version 1 (SYSV), 
dynamically linked, interpreter /lib/ld.so.1, stripped
muller@gcc186:~/pas/check$ qemu-ppc64 -cpu power7  ./twide1
-bash: qemu-ppc64: command not found
muller@gcc186:~/pas/check$ ~/sys-root/bin/qemu-ppc64 -cpu power7  ./twide1
qemu-ppc64: ./twide1: Invalid ELF image for this architecture
muller@gcc186:~/pas/check$ ~/sys-root/bin/qemu-ppc64 --version
qemu-ppc64 version 7.0.0
Copyright (c) 2003-2022 Fabrice Bellard and the QEMU Project developers
muller@gcc186:~/pas/check$ ~/gnu/qemu/build-qemu-7.1.0-rc2/qemu-ppc64 -cpu 
power7  ./twide1
qemu-ppc64: ./twide1: Invalid ELF image for this architecture

So qemu-ppc64 (7.0.0 and 7.1.0-rc2) is only able to run 64-bit binaries.

Pierre