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

[Fei Yang]

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

It's strange that I can't reproduce the build warning/error when compiling the following test with g++-9 shipped with Ubuntu 22.04.1 LTS. Do you know why? Or maybe you can try the same g++-9 to see?


#include <cstdint>

uintptr_t get_addr() {
  alignas(64) char memory[64];

  return (uintptr_t)&memory[0];
}


$ g++-9 -v
Using built-in specs.
COLLECT_GCC=g++-9
COLLECT_LTO_WRAPPER=/usr/lib/gcc/riscv64-linux-gnu/9/lto-wrapper
Target: riscv64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu 9.5.0-6ubuntu2' --with-bugurl=file:///usr/share/doc/gcc-9/README.Bugs --enable-languages=c,ada,c++,go,d,fortran,objc,obj-c++,gm2 --prefix=/usr --with-gcc-major-version-only --program-suffix=-9 --program-prefix=riscv64-linux-gnu- --enable-shared --enable-linker-build-id --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --libdir=/usr/lib --enable-nls --enable-clocale=gnu --enable-libstdcxx-debug --enable-libstdcxx-time=yes --with-default-libstdcxx-abi=new --enable-gnu-unique-object --disable-libitm --disable-libsanitizer --disable-libquadmath --disable-libquadmath-support --enable-plugin --enable-default-pie --with-system-zlib --with-target-system-zlib=auto --enable-objc-gc=auto --enable-multiarch --disable-werror --disable-multilib --with-arch=rv64imafdc --with-abi=lp64d --enable-checking=release --build=riscv64-linux-gnu --host=riscv64-linux-gnu --target=riscv64-linux-gnu
Thread model: posix
gcc version 9.5.0 (Ubuntu 9.5.0-6ubuntu2)


$ g++-9  -Wall -S -O2 foo.cpp

-------------

PR Comment: https://git.openjdk.org/jdk/pull/21376#issuecomment-2399674049