Re: [PATCH 0/3] semihosting: Fix a few semihosting bugs

[Sean Anderson <sean.anderson@linux.dev>]

On 10/20/25 11:03, Alex Bennée wrote:
> Sean Anderson <sean.anderson@linux.dev> writes:
> 
>> While discussing [1], it came to my attention that QEMU does not
>> properly truncate/error SYS_FLEN on 32-bit systems.
> 
> TIL that semihostingfs was a thing!
> 
>> Fix this, and some
>> other bugs with GDB File I/O that I found while working on this series.
>> That said, GDB File I/O has been substantially broken for two years now,
>> so it makes me wonder if anyone actually uses it!
> 
> I suspect this is at the upper end of things to use semihosting for as
> its real purpose is to help bootstrap things on the barest of metal
> until you have enough bits going to selfhost. In QEMU land it is a
> convenient way to do host calls for test cases.
> 
> We don't have much actual testing of semihosting in the tree although I
> do run Peter's semihosting tests from time to time:
> 
>   https://git.linaro.org/people/peter.maydell/semihosting-tests.git/
> 
> the tests do include flen() but obviously don't cover the extreme
> filesize cases or overflow.
> 
>> It would certainly
>> simplify the implementation if we didn't have to support it.
> 
> While semihosting does have the concept of optional extensions SYS_FLEN
> is not one of them.

The above comments refer to GDB File I/O, which currently cannot open
files due to the problem fixed in patch 1/3. FLEN is not really broken
for most use-cases (as long as the user doesn't access large files).

--Sean