Re: [PATCH] semihosting/arm-compat: Have TARGET_SYS_EXIT[_EXTENDED] return signed

[Philippe Mathieu-Daudé]

Hi Peter,

On 16/10/23 18:08, Peter Maydell wrote:
> On Thu, 5 Oct 2023 at 07:27, Philippe Mathieu-Daudé <philmd@linaro.org> wrote:
> > Per the "Semihosting for AArch32 and AArch64" spec. v2 (2023Q3) [*]:
> >
> >    6.5   SYS_EXIT (0x18)
> >    6.5.2   Entry (64-bit)
> >
> >      On entry, the PARAMETER REGISTER contains a pointer to
> >      a two-field argument block:
> >
> >      . field 1
> >        The exception type, which is one of the set of reason
> >        codes in the above tables.
> >
> >      . field 2
> >        A subcode, whose meaning depends on the reason code in
> >        field 1.
> >
> >      In particular, if field 1 is ADP_Stopped_ApplicationExit
> >      then field 2 is an exit status code, as passed to the C
> >      standard library exit() function. [...]
> >
> > Having libc exit() is declared as:
> >
> >    LIBRARY
> >         Standard C Library (libc, -lc)
> >
> >    SYNOPSIS
> >
> >         void
> >         exit(int status);
> >
> > the status is expected to be signed.
> >
> > [*] 
> > https://github.com/ARM-software/abi-aa/blob/2023q3-release/semihosting/semihosting.rst#652entry-64-bit
>
> Is this actually a visible change in behaviour? It makes
> more sense to use 'int', I agree, but unless I'm confused
> about C type conversions then I don't think it actually
> changes the result in any case, does it?  Given we start with a
> guest 64 or 32 bit signed integer value and put it into a
> 'target_ulong' (arg1), it doesn't seem to me to make a
> difference whether we put it into a 'uint32_t' or an
> 'int' (ret) before passing it to either exit() or
> gdb_exit() (which both take 'int')...

There should be no behavioral change, it is a cleanup
to avoid asking "why are we using a uint32_t here?" in
future reviews. Do you rather I mention it in the commit
description?

Regards,

Phil.