Re: [Qemu-devel] [RFC 24/28] target-xtensa: implement SIMCALL

[Peter Maydell]

On 4 May 2011 20:48, Blue Swirl <address@hidden> wrote:
> On Wed, May 4, 2011 at 3:59 AM, Max Filippov <address@hidden> wrote:
>> Tensilica iss provides support for applications running in freestanding
>> environment through SIMCALL command. It is used by Tensilica libc to
>> access argc/argv, for file I/O, etc.
>>
>> Signed-off-by: Max Filippov <address@hidden>
>> ---
>>  target-xtensa/helpers.h   |    1 +
>>  target-xtensa/op_helper.c |    7 ++
>>  target-xtensa/simcall.c   |  157 
>> +++++++++++++++++++++++++++++++++++++++++++++

The existing simcall/semihosting implementations
are in arm-semi.c and m68k-semi.c in the top level
directory. I think xtensa should do the same
(unless somebody wants to propose moving arm and
m68k instead...)

>> +void HELPER(simcall)(void)
>> +{
>> +    simcall(env->regs);
>
> Maybe this should be enabled only with -semihosting parameter, like
> ARM and m68k. Consider for example what could happen if this would be
> issued from userland when used with an OS.

+1 for consistency with arm/m68k. This applies more generally:
for example if there's any chance there might be a linux-user
implementation for xtensa then you want to use the softmmu-semi.h
helpers so the memory access will work in both setups.

m68k and ARM also both funnel semihosting through the interrupt/
exception mechanisms; I haven't figured out if there's a good
reason for that that would make it worth copying in xtensa :-)

>> +    SYS_exit = 1,

> I think these names may easily conflict with system defines, please
> use for example TARGET_SYS_exit etc.

Renaming's safe, but as it happens arm-semi.c has been
using SYS_EXIT &c with no problems, so I don't think it's
a big deal either way.

-- PMM