On 1/9/20 3:12 PM, Masahiro Yamada wrote:
> According to the specification "Semihosting for AArch32 and Aarch64",
> the SYS_OPEN operation should return:
>
> - A nonzero handle if the call is successful
> - -1 if the call is not successful
>
> So, it should never return 0.
>
> Prior to commit 35e9a0a8ce4b ("target/arm/arm-semi: Make semihosting
> code hand out its own file descriptors"), the guest fd matched to the
> host fd. It returned a nonzero handle on success since the fd 0 is
> already used for stdin.
>
> Now that the guest fd is the index of guestfd_array, it starts from 0.
>
> I noticed this issue particularly because Trusted Firmware-A built with
> PLAT=qemu is no longer working. Its io_semihosting driver only handles
> a positive return value as a valid filehandle.
>
> Basically, there are two ways to fix this:
>
> - Use (guestfd - 1) as the index of guestfs_arrary. We need to insert
> increment/decrement to convert the guestfd and the array index back
> and forth.
>
> - Keep using guestfd as the index of guestfs_array. The first entry
> of guestfs_array is left unused.
>
> I thought the latter is simpler. We end up with wasting a small piece
> of memory for the unused first entry of guestfd_array, but this is
> probably not a big deal.
>
> Fixes: 35e9a0a8ce4b ("target/arm/arm-semi: Make semihosting code hand out its
> own file descriptors")
> Signed-off-by: Masahiro Yamada <masahi...@kernel.org>
> ---
Reviewed-by: Richard Henderson <richard.hender...@linaro.org>
r~
