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

["Alex Bennée" <alex.bennee@linaro.org>]

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.

>
> [1] https://lore.kernel.org/u-boot/20251017195322.GF6688@bill-the-cat/T/#m493c42570d3103b8c606c5f50faeb78d27719de6
>
>
> Sean Anderson (3):
>   gdbstub: Fix %s formatting
>   semihosting: Fix GDB File-I/O FLEN
>   semihosting: Check for overflow in FLEN on 32-bit systems
>
>  gdbstub/syscalls.c            |  2 +-
>  semihosting/arm-compat-semi.c | 22 +++++++++++++++-------
>  2 files changed, 16 insertions(+), 8 deletions(-)

-- 
Alex Bennée
Virtualisation Tech Lead @ Linaro