Re: [PATCH] target/arm/arm-semi: fix SYS_OPEN to return nonzero filehandle

[Richard Henderson <richard.henderson@linaro.org>]

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 <masahiroy@kernel.org>
> ---

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>


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