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

[Peter Maydell]

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')...

-- PMM