Is returning a value != '0' or '1' as jboolean from a JNI function legal?

[Aleksey Shipilev]

On 08/17/2018 05:12 PM, Volker Simonis wrote:
> The offending code in Console_md.c looks as follows:
> 
> #define ECHO    8
> 
> JNIEXPORT jboolean JNICALL
> Java_java_io_Console_echo(...) {
> 
>     jboolean old;
>     ...
>     old = (tio.c_lflag & ECHO);
>     ...
>     return old;
> }
> 
> The intention of this code is to return "true" if the ECHO flag was
> set but it really returns the value of ECHO (which is defined as '8'
> in a system header).
> 
> The question now is, if a Java SE compatible VM guarantees that any
> arbitrary, non-zero valued jboolean will be interpreted as "JNI_TRUE"
> and only a zero valued jboolean will be interpreted as "JNI_FALSE"?
> 
> Or, the other way round, is the normalization performed by the HotSpot
> result handlers necessary (i.e. enforced by the specification) or just
> a convenience to fix broken code like the above from Console.echo()?

I think this is intentional aftermath of boolean value normalization:
  https://bugs.openjdk.java.net/browse/JDK-8161720

So, Java_java_io_Console_echo looks broken and needs to be fixed, by e.g.:

-   old = (tio.c_lflag & ECHO);
+   old = (tio.c_lflag & ECHO) != 0;

Thanks,
-Aleksey