RFR: 8254270: linux 32 bit build doesn't compile libjdwp/log_messages.c [v2]

[Coleen Phillimore]

On Thu, 5 Nov 2020 19:41:25 GMT, Claes Redestad <redestad at openjdk.org> wrote:

>> ... so the problem would be that the compiler does not believe us that millisecs will be always <1000. And there is no way to truncate output for numerical format specifiers.
>> 
>> One solution could be to first print the millisecs to a buffer large enough to hold MAX_INT. And then print that buffer as a string, which can be truncated with precision.
>> 
>> char tmp[10 + 1];
>> snprintf(tmp, sizeof(tmp), "%d", millisecs);
>> snprintf(tbuf, ltbuf, "%s.%.3s %s", timestamp_date_time, tmp, timestamp_timezone);
>> 
>> That may be enough to shut the compiler up.
>
>> ... so the problem would be that the compiler does not believe us that millisecs will be always <1000. And there is no way to truncate output for numerical format specifiers.
> 
> Interesting, and a reasonable explanation. Odd this doesn't get caught by the 64-bit build
> 
>> 
>> One solution could be to first print the millisecs to a buffer large enough to hold MAX_INT. And then print that buffer as a string, which can be truncated with precision.
>> 
>> ```
>> char tmp[10 + 1];
>> snprintf(tmp, sizeof(tmp), "%d", millisecs);
>> snprintf(tbuf, ltbuf, "%s.%.3s %s", timestamp_date_time, tmp, timestamp_timezone);
>> ```
>> 
>> That may be enough to shut the compiler up.
> 
> It'd be interesting to see if statically limiting the value printed to be < 1000 would also convince the compiler, e.g.
> `snprintf(tbuf, ltbuf, "%s.%.3d %s", timestamp_date_time, millisecs % 1000, timestamp_timezone);`
> 
> (I'm not sure a perfect solution is worth our while here, but seeing we've gotten this far down the rabbit hole..)

I didn't see your comment @cl4es and I tested out Thomas's solution and that compiles and seems to make sense.

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PR: https://git.openjdk.java.net/jdk/pull/1067