RFR: 8314114: Fix -Wconversion warnings in os code, primarily linux [v2]

[Coleen Phillimore]

On Mon, 14 Aug 2023 02:16:06 GMT, David Holmes <dholmes at openjdk.org> wrote:

>> It doesn't.  I got a Wconversion warning converting to int here.  I wouldn't have changed it otherwise.
>> 
>> src/hotspot/os/linux/os_linux.cpp:404:21: warning: conversion from 'long int' to 'int' may change value [-Wconversion]
>>   404 |   int rslt = syscall(SYS_gettid);
>>       |              ~~~~~~~^~~~~~~~~~~~
>
> I have to prove I'm not an idiot here :). This is from the Linux manpage:
> 
> NAME
>        syscall - indirect system call
> 
> SYNOPSIS
>        #define _GNU_SOURCE         /* See feature_test_macros(7) */
>        #include <unistd.h>
>        #include <sys/syscall.h>   /* For SYS_xxx definitions */
> 
>        int syscall(int number, ...);
> 
> But yes the definition in unistd.h is `long int'.
> 
> In platform specific code such as this, when a function returns a long then perhaps we should type the result variable as a long as well, rather than forcing to a 64-bit type?

We discussed purging 'long' from the code but since this is platform specific code, then we can use long here to match the type of syscall.

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PR Review Comment: https://git.openjdk.org/jdk/pull/15229#discussion_r1293382554