Re: [PATCH] target/sparc: Handle FPRS correctly on big-endian hosts

["Philippe Mathieu-Daudé" <philmd@linaro.org>]

Hi Peter,

On 14/7/23 19:26, Peter Maydell wrote:
> In CPUSparcState we define the fprs field as uint64_t.  However we
> then refer to it in translate.c via a TCGv_i32 which we set up with
> tcg_global_mem_new_ptr().  This means that on a big-endian host when
> the guest does something to writo te the FPRS register this value
> ends up in the wrong half of the uint64_t, and the QEMU C code that
> refers to env->fprs sees the wrong value.  The effect of this is that
> guest code that enables the FPU crashes with spurious FPU Disabled
> exceptions.  In particular, this is why
>   tests/avocado/machine_sparc64_sun4u.py:Sun4uMachine.test_sparc64_sun4u
> times out on an s390 host.
> 
> There are multiple ways we could fix this; since there are actually
> only three bits in the FPRS register and the code in translate.c
> would be a bit painful to convert to dealing with a TCGv_i64, change
> the type of the CPU state struct field to match what translate.c is
> expecting.
> 
> (None of the other fields referenced by the r32[] array in
> sparc_tcg_init() have the wrong type.)
> 
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
> ---
> Another in my occasional series of "fix an avocado failure on
> s390" Friday afternoon patches :-)

:)

> diff --git a/target/sparc/gdbstub.c b/target/sparc/gdbstub.c
> index a1c8fdc4d55..bddb9609b7b 100644
> --- a/target/sparc/gdbstub.c
> +++ b/target/sparc/gdbstub.c
> @@ -96,7 +96,10 @@ int sparc_cpu_gdb_read_register(CPUState *cs, GByteArray *mem_buf, int n)
>       case 83:
>           return gdb_get_regl(mem_buf, env->fsr);
>       case 84:
> -        return gdb_get_regl(mem_buf, env->fprs);
> +    {
> +        target_ulong fprs = env->fprs;
> +        return gdb_get_regl(mem_buf, fprs);

Why not return gdb_get_reg32() ?

> +    }