g++ seems to have segfaulted whild building openjdk-lts (openjdk-11) on focal/riscv-64 (precisely, while running a hotspot test):

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( /bin/rm -f /<<PKGBUILDDIR>>/build/hotspot/variant-zero/libjvm/gtest/objs/test_align.o.log && /usr/bin/riscv64-linux-gnu-g++-9 -MMD -MF /<<PKGBUILDDIR>>/build/hotspot/variant-zero/libjvm/gtest/objs/test_align.d.tmp -I/<<PKGBUILDDIR>>/build/hotspot/variant-zero/libjvm/gtest/objs/precompiled -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -D__STDC_CONSTANT_MACROS -D_GNU_SOURCE -D_REENTRANT -pipe -fno-rtti -fno-exceptions -fvisibility=hidden -fno-strict-aliasing -fno-omit-frame-pointer -fcheck-new -fstack-protector -std=gnu++98 -DLIBC=gnu -DSUPPORTS_CLOCK_MONOTONIC -DLINUX -Wpointer-arith -Wsign-compare -Wunused-function -Wunused-value -Woverloaded-virtual -fPIC -fmacro-prefix-map=/<<PKGBUILDDIR>>/= -DVM_LITTLE_ENDIAN -D_LP64=1 -fno-delete-null-pointer-checks -fno-lifetime-dse -Wno-format-zero-length -Wtype-limits -Wuninitialized -Wdate-time -D_FORTIFY_SOURCE=2 -g -fdebug-prefix-map=/<<PKGBUILDDIR>>=. -Wformat -fno-stack-protector -Wno-deprecated-declarations -DPRODUCT -DTARGET_ARCH_zero -DINCLUDE_SUFFIX_OS=_linux -DINCLUDE_SUFFIX_CPU=_zero -DINCLUDE_SUFFIX_COMPILER=_gcc -DTARGET_COMPILER_gcc -DRISCV -DHOTSPOT_LIB_ARCH='"riscv64"' -DZERO -DCC_INTERP -DZERO_LIBARCH='"riscv64"' -DINCLUDE_JVMCI=0 -DINCLUDE_AOT=0 -DINCLUDE_G1GC=0 -DINCLUDE_EPSILONGC=0 -DINCLUDE_ZGC=0 -DINCLUDE_SHENANDOAHGC=0 -DINCLUDE_JFR=0 -I/<<PKGBUILDDIR>>/src/hotspot/share -I/<<PKGBUILDDIR>>/src/hotspot/os/linux -I/<<PKGBUILDDIR>>/src/hotspot/os/posix -I/<<PKGBUILDDIR>>/src/hotspot/cpu/zero -I/<<PKGBUILDDIR>>/src/hotspot/os_cpu/linux_zero -I/<<PKGBUILDDIR>>/build/hotspot/variant-zero/gensrc -I/<<PKGBUILDDIR>>/src/hotspot/share/precompiled -I/<<PKGBUILDDIR>>/src/hotspot/share/include -I/<<PKGBUILDDIR>>/src/hotspot/os/posix/include -I/<<PKGBUILDDIR>>/build/support/modules_include/java.base -I/<<PKGBUILDDIR>>/build/support/modules_include/java.base/linux -I/<<PKGBUILDDIR>>/src/java.base/share/native/libjimage -Wdate-time -D_FORTIFY_SOURCE=2 -g -fdebug-prefix-map=/<<PKGBUILDDIR>>=. -Wformat -fno-stack-protector -Wno-deprecated-declarations -Wdate-time -D_FORTIFY_SOURCE=2 -DDEB_MULTIARCH="\"riscv64-linux-gnu\"" -I/<<PKGBUILDDIR>>/test/fmw/gtest -I/<<PKGBUILDDIR>>/test/fmw/gtest/include -I/<<PKGBUILDDIR>>/test/hotspot/gtest -g -Wno-undef -Wno-stringop-overflow -O3 -c -o /<<PKGBUILDDIR>>/build/hotspot/variant-zero/libjvm/gtest/objs/test_align.o /<<PKGBUILDDIR>>/test/hotspot/gtest/utilities/test_align.cpp > >(/usr/bin/tee -a /<<PKGBUILDDIR>>/build/hotspot/variant-zero/libjvm/gtest/objs/test_align.o.log) 2> >(/usr/bin/tee -a /<<PKGBUILDDIR>>/build/hotspot/variant-zero/libjvm/gtest/objs/test_align.o.log >&2) || ( exitcode=$? && /bin/cp /<<PKGBUILDDIR>>/build/hotspot/variant-zero/libjvm/gtest/objs/test_align.o.log /<<PKGBUILDDIR>>/build/make-support/failure-logs/hotspot_variant-zero_libjvm_gtest_objs_test_align.o.log && /bin/cp /<<PKGBUILDDIR>>/build/hotspot/variant-zero/libjvm/gtest/objs/test_align.o.cmdline /<<PKGBUILDDIR>>/build/make-support/failure-logs/hotspot_variant-zero_libjvm_gtest_objs_test_align.o.cmdline && exit $exitcode ) )
Compiling test_arguments.cpp (for libjvm.so)

riscv64-linux-gnu-g++-9: internal compiler error: Segmentation fault signal terminated program cc1plus  

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I don't have any more information on this at the moment. But this bug seemed relevant, hence the comment!