[PATCH] fs: semihosting: Use correct variable for error check

[Sean Anderson]

On 10/2/25 11:07, Heinrich Schuchardt wrote:
> On 10/2/25 16:36, Sean Anderson wrote:
>> On 10/2/25 05:52, Heinrich Schuchardt wrote:
>>> On 10/2/25 11:39, Andrew Goodbody wrote:
>>>> After calling a function that can return an error, the test to detect
>>>> that error should use the return value not a different variable. Fix it.
>>>>
>>>> This issue was found by Smatch.
>>>>
>>>
>>> Fixes: f676b45151c3 ("fs: Add semihosting filesystem")
>>>
>>>> Signed-off-by: Andrew Goodbody <andrew.goodbody at linaro.org>
>>>> ---
>>>>    fs/semihostingfs.c | 2 +-
>>>>    1 file changed, 1 insertion(+), 1 deletion(-)
>>>>
>>>> diff --git a/fs/semihostingfs.c b/fs/semihostingfs.c
>>>> index 77e39ca407e4d240a1fd573497c5b6b908816454..9d7a136b9ba9b035545b34b31df58e2d65de7db9 100644
>>>> --- a/fs/semihostingfs.c
>>>> +++ b/fs/semihostingfs.c
>>>> @@ -35,7 +35,7 @@ static int smh_fs_read_at(const char *filename, loff_t pos, void *buffer,
>>>>        }
>>>>        if (!maxsize) {
>>>>            size = smh_flen(fd);
>>>> -        if (ret < 0) {
>>>> +        if (size < 0) {
>>>
>>> The ARM specification (https://cas5-0-urlprotect.trendmicro.com:443/wis/clicktime/v1/query?url=https%3a%2f%2fdeveloper.arm.com%2fdocumentation%2fdui0203%2fj%2fsemihosting%2fsemihosting%2doperations%2fsys%2dflen%2d%2d0x0c%2d&umid=f17ab8fc-2d9d-4cce-91e2-e7e66f117613&rct=1759398729&auth=d807158c60b7d2502abde8a2fc01f40662980862-e0799d2d4d61f93cae033d54733c8fa50ef84918) has:
>>>
>>> SYS_FLEN (0x0C)
>>>
>>> Returns the length of a specified file.
>>> On exit, R0 contains:
>>>      the current length of the file object, if the call is successful
>>>      -1 if an error occurs.
>>>
>>> Please, consider that the file length on 32bit systems may exceed 2^31 You must not consider this as an error.
>>>
>>> %s/if (size < 0)/if (size == -1L)/
>>
>> This cannot occur because on a 32-bit system SYS_FLEN only returns
>> 32-bits of information. The host must detect files that exceed 2 GiB in
>> size and return -1 (simulating EOVERFLOW).
> 
> I don't think so.
> 
> QEMU will read into the st_size field of a struct stat and copy that value to the return value. The st_size field will have at least 64 bits on a 64 bit system. And copying to the 32 bit target will simply truncate it.
> 
> Expect overruns for files that are larger than 0xffffffff.

Yes. And there's nothing we can do about this. If there is a 9 GiB file,
SYS_FLEN will report it as a 1 GiB file. This is a bug in QEMU (and
OpenOCD too) that we shouldn't attempt to work around in U-Boot.

--Sean