Arduino IDEでSipeed Maixシリーズのコンパイラオプションを変更する方法
(自己責任でお願いします)

Windowsの場合
C:\Users\username\AppData\Local\Arduino15\packages\Maixduino\hardware\k210\0.3.11\platform.txt
このファイルを編集する(usernameは各自のWindowsのユーザ名に読み替えてください)

Linuxの場合
~/.arduino15/packages/Maixduino/hardware/k210/0.3.11\platform.txt
このファイルを編集する

compiler.both.flags=-mcmodel=medany -mabi=lp64f -march=rv64imafc -fno-common -ffunction-sections -fdata-sections -fstrict-volatile-bitfields -fno-zero-initialized-in-bss -Os -ggdb -Wall -Werror=all -Wno-error=unused-function -Wno-error=unused-but-set-variable -Wno-error=unused-variable -Wno-error=deprecated-declarations -Wextra -Werror=frame-larger-than=65536 -Wno-unused-parameter -Wno-sign-compare -Wno-error=missing-braces -Wno-error=return-type -Wno-error=pointer-sign -Wno-missing-braces -Wno-strict-aliasing -Wno-implicit-fallthrough -Wno-missing-field-initializers -Wno-int-to-pointer-cast -Wno-error=comment -Wno-error=logical-not-parentheses -Wno-error=duplicate-decl-specifier -Wno-error=parentheses -Wno-error=narrowing -Wno-error=unused-value

23行目あたりのこの部分をrv64imafcをrv64gcに変更
compiler.both.flags=-mcmodel=medany -mabi=lp64f -march=rv64gc -fno-common -ffunction-sections -fdata-sections -fstrict-volatile-bitfields -fno-zero-initialized-in-bss -Os -ggdb -Wall -Werror=all -Wno-error=unused-function -Wno-error=unused-but-set-variable -Wno-error=unused-variable -Wno-error=deprecated-declarations -Wextra -Werror=frame-larger-than=65536 -Wno-unused-parameter -Wno-sign-compare -Wno-error=missing-braces -Wno-error=return-type -Wno-error=pointer-sign -Wno-missing-braces -Wno-strict-aliasing -Wno-implicit-fallthrough -Wno-missing-field-initializers -Wno-int-to-pointer-cast -Wno-error=comment -Wno-error=logical-not-parentheses -Wno-error=duplicate-decl-specifier -Wno-error=parentheses -Wno-error=narrowing -Wno-error=unused-value


もしくはさらに-Osを-O2に変更してrv64imafcをrv64gcに変更-Osを-O2に変更
compiler.both.flags=-mcmodel=medany -mabi=lp64f -march=rv64gc -fno-common -ffunction-sections -fdata-sections -fstrict-volatile-bitfields -fno-zero-initialized-in-bss -O2 -ggdb -Wall -Werror=all -Wno-error=unused-function -Wno-error=unused-but-set-variable -Wno-error=unused-variable -Wno-error=deprecated-declarations -Wextra -Werror=frame-larger-than=65536 -Wno-unused-parameter -Wno-sign-compare -Wno-error=missing-braces -Wno-error=return-type -Wno-error=pointer-sign -Wno-missing-braces -Wno-strict-aliasing -Wno-implicit-fallthrough -Wno-missing-field-initializers -Wno-int-to-pointer-cast -Wno-error=comment -Wno-error=logical-not-parentheses -Wno-error=duplicate-decl-specifier -Wno-error=parentheses -Wno-error=narrowing -Wno-error=unused-value