Re: [Xen-devel] [PATCH] xen/console: Fix build when CONFIG_DEBUG_TRACE=y

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 19/08/2019 19:37, Julien Grall wrote:
> Hi Andrew,
>
> On 8/19/19 7:04 PM, Andrew Cooper wrote:
>> On 19/08/2019 19:01, Julien Grall wrote:
>>> Commit b5e6e1ee8da "xen/console: Don't treat NUL character as the end
>>> of the buffer" extended sercon_puts to take the number of character
>>> to print in argument.
>>>
>>> Sadly, a couple of couple of the callers in debugtrace_dump_worker()
>>> were not converted. This result to a build failure when enabling
>>> CONFIG_DEBUG_TRACE.
>>>
>>> Spotted by Travis using randconfig
>>> Signed-off-by: Julien Grall <julien.grall@xxxxxxx>
>>> ---
>>>   xen/drivers/char/console.c | 5 +++--
>>>   1 file changed, 3 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/xen/drivers/char/console.c b/xen/drivers/char/console.c
>>> index 2c14c2ca73..924d4971ca 100644
>>> --- a/xen/drivers/char/console.c
>>> +++ b/xen/drivers/char/console.c
>>> @@ -1185,11 +1185,12 @@ static void debugtrace_dump_worker(void)
>>>         /* Print oldest portion of the ring. */
>>>       ASSERT(debugtrace_buf[debugtrace_bytes - 1] == 0);
>>> -    sercon_puts(&debugtrace_buf[debugtrace_prd]);
>>> +    sercon_puts(&debugtrace_buf[debugtrace_prd],
>>> +                strlen(&debugtrace_buf[debugtrace_prd]));
>>
>> Isn't this just debugtrace_bytes - debugtrace_prd - 1 ?
>
> I tried and it resulted to print a lot of @^ on the console. This is
> because the ring may not be full.
>
> So the portion between debugtrace_prd and debugtrace_bytes will be
> full of zero.
>
> Looking at the code again, I think this portion and either be full of
> zero character or full of non-zero character. In other word, a mix
> would not be possible. So how about:
>
> if ( debugtrace_buf[debugtrace_prd] != '\0' )
>   sercon_puts(&debugtrace_buf[debugtrace_prd],
>               debugtrace_bytes - debugtrace_prd - 1);

LGTM.  Acked-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

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