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

[Dean Long]

On Thu, 10 Aug 2023 15:22:07 GMT, Coleen Phillimore <coleenp at openjdk.org> wrote:

> This change fixes various -Wconversion warnings from files in the os directories and related, widening types or adding checked_cast<> where narrowing.
> Tested with tier1 on linux/macosx/windows and tier1-4 on linux-x64-debug, windows-x64-debug.

src/hotspot/os/linux/cgroupSubsystem_linux.cpp line 497:

> 495: 
> 496:   if (quota > -1 && period > 0) {
> 497:     quota_count = (int)ceilf((float)quota / (float)period);

Should be OK except for the pathological case of quota near INT_MAX and period == 1.

src/hotspot/os/linux/os_linux.cpp line 1604:

> 1602: 
> 1603:   Elf32_Ehdr elf_head;
> 1604:   size_t diag_msg_max_length=ebuflen-strlen(ebuf);

Underflow will result in very large unsigned number.  Do we need helper functions for unsigned math that checks for underflow/overflow?

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PR Review Comment: https://git.openjdk.org/jdk/pull/15229#discussion_r1290605284
PR Review Comment: https://git.openjdk.org/jdk/pull/15229#discussion_r1290619501