Re: [Qemu-devel] [PATCH] linux-user: Fix trampoline code for CRIS

[Edgar E. Iglesias]

On Sat, Feb 01, 2014 at 12:09:06PM +0000, Peter Maydell wrote:
> On 1 February 2014 08:41, Stefan Weil <address@hidden> wrote:
> > __put_user can write bytes, words (2 bytes) or longwords (4 bytes).
> > Here obviously words should have been written, but bytes were written,
> > so values like 0x9c5f were truncated to 0x5f.
> >
> > Fix this by changing retcode from uint8_t to to uint16_t in
> > target_signal_frame and also in the unused rt_signal_frame.
> 
> I believe this will do the right thing. The other possible approach
> would be to do what the kernel does here (and what some of
> the QEMU code for other targets does, eg x86) and put in the cast:
> 
> http://lxr.free-electrons.com/source/arch/cris/arch-v10/kernel/signal.c#L261
> 
> 261                 /* This is movu.w __NR_sigreturn, r9; break 13; */
> 262                 err |= __put_user(0x9c5f,         (short
> __user*)(frame->retcode+0));
> 263                 err |= __put_user(__NR_sigreturn, (short
> __user*)(frame->retcode+2));
> 264                 err |= __put_user(0xe93d,         (short
> __user*)(frame->retcode+4));
> 
> (obviously we'd want "(uint16_t *)").
> 
> Since CRIS looks (from a scan through its translate.c) like
> a variable-width instruction set (in the sense that insns can
> have immediate operands which might be 1/2/4 bytes long)
> I think there's an argument here for following the kernel and
> keeping retcode[] a byte array, for the implausible case where
> we want to change the trampoline sequence to include an
> insn with a 1 byte immediate value or something.
> 
> Either way I believe the endianness handling should be correct
> since __put_user does host-to-target swapping for us.
> 
> It might be possible to test this by extracting some of the
> userspace binaries from the cris system emulation test image
> on the QEMU wiki (or it might not).

Hi,

I've tested the patch, it works. CRIS insn stream is always 16bit
aligned, I think Stefans patch is OK.

Cheers,
Edgar