RFR: 8341586: RISC-V: build fail with gcc9

[Magnus Ihse Bursie]

On Sun, 6 Oct 2024 13:28:30 GMT, SendaoYan <syan at openjdk.org> wrote:

> Hi all,
> The `src/hotspot/cpu/riscv/icache_riscv.cpp` build fails `riscv_flush_icache.cpp:51:29: error: requested alignment 64 is larger than 16 [-Werror=attributes]` with gcc9. Alignment 16 will be enough, though the [NR_riscv_flush_icache syscall](https://github.com/torvalds/linux/blob/master/tools/arch/riscv/include/uapi/asm/unistd.h) doesn't reqiure alignment.
> 
> Addiontional testing:
> 
> - [x] riscv native build with release conf and slowdebug conf
> - [ ] jtreg tier1 tests with release build

gcc 9 is not supported for mainline. If this is required for 21 and older, it should go in there and then be backported from there. I do not think this PR should be included in mainline.

Please open a separate JBS issue for the incorrect detection of gcc version by configure.

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PR Comment: https://git.openjdk.org/jdk/pull/21376#issuecomment-2399893428