Using `riscv64-unknown-elf-g++` to link rust static lib failed - rust

Question

I try to use riscv64-unknown-elf-g++ which is rv64imac architecture to compile C code with rust static lib.
The simple example is https://github.com/zzhengzhuo/base_bin .
When I use riscv64-unknown-elf-gcc, it works well. But when I use riscv64-unknown-elf-g++, it reports errors like this:
riscv64-unknown-elf-g++ -Ibase_lib -v -o build/base_bin main.c base_lib/target/riscv64imac-unknown-none-elf/release/libbase_lib.a
Using built-in specs.
COLLECT_GCC=riscv64-unknown-elf-g++
COLLECT_LTO_WRAPPER=/opt/riscv/libexec/gcc/riscv64-unknown-elf/11.1.0/lto-wrapper
Target: riscv64-unknown-elf
Configured with: /home/zhengzhuo/riscv-gnu-toolchain/riscv-gcc/configure --target=riscv64-unknown-elf --prefix=/opt/riscv --disable-shared --disable-threads --enable-languages=c,c++ --with-system-zlib --enable-tls --with-newlib --with-sysroot=/opt/riscv/riscv64-unknown-elf --with-native-system-header-dir=/include --disable-libmudflap --disable-libssp --disable-libquadmath --disable-libgomp --disable-nls --disable-tm-clone-registry --src=.././riscv-gcc --enable-multilib --with-abi=lp64 --with-arch=rv64imac --with-tune=rocket 'CFLAGS_FOR_TARGET=-Os -mcmodel=medlow' 'CXXFLAGS_FOR_TARGET=-Os -mcmodel=medlow'
Thread model: single
Supported LTO compression algorithms: zlib
gcc version 11.1.0 (GCC)
COLLECT_GCC_OPTIONS='-I' 'base_lib' '-v' '-o' 'build/base_bin' '-mtune=rocket' '-march=rv64imac' '-mabi=lp64' '-march=rv64imac' '-dumpdir' 'build/base_bin-'
/opt/riscv/libexec/gcc/riscv64-unknown-elf/11.1.0/cc1plus -quiet -v -I base_lib main.c -quiet -dumpdir build/base_bin- -dumpbase main.c -dumpbase-ext .c -mtune=rocket -march=rv64imac -mabi=lp64 -march=rv64imac -version -o /tmp/ccpwBEao.s
GNU C++17 (GCC) version 11.1.0 (riscv64-unknown-elf)
compiled by GNU C version 9.4.0, GMP version 6.2.0, MPFR version 4.0.2, MPC version 1.1.0, isl version none
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
ignoring nonexistent directory "/opt/riscv/riscv64-unknown-elf/usr/local/include"
ignoring duplicate directory "/opt/riscv/riscv64-unknown-elf/include"
#include "..." search starts here:
#include <...> search starts here:
base_lib
/opt/riscv/lib/gcc/riscv64-unknown-elf/11.1.0/../../../../riscv64-unknown-elf/include/c++/11.1.0
/opt/riscv/lib/gcc/riscv64-unknown-elf/11.1.0/../../../../riscv64-unknown-elf/include/c++/11.1.0/riscv64-unknown-elf
/opt/riscv/lib/gcc/riscv64-unknown-elf/11.1.0/../../../../riscv64-unknown-elf/include/c++/11.1.0/backward
/opt/riscv/lib/gcc/riscv64-unknown-elf/11.1.0/include
/opt/riscv/lib/gcc/riscv64-unknown-elf/11.1.0/include-fixed
/opt/riscv/lib/gcc/riscv64-unknown-elf/11.1.0/../../../../riscv64-unknown-elf/include
End of search list.
GNU C++17 (GCC) version 11.1.0 (riscv64-unknown-elf)
compiled by GNU C version 9.4.0, GMP version 6.2.0, MPFR version 4.0.2, MPC version 1.1.0, isl version none
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
Compiler executable checksum: 70c8dfad8a0cf9a76df8ead2812f5775
COLLECT_GCC_OPTIONS='-I' 'base_lib' '-v' '-o' 'build/base_bin' '-mtune=rocket' '-march=rv64imac' '-mabi=lp64' '-march=rv64imac' '-dumpdir' 'build/base_bin-'
/opt/riscv/lib/gcc/riscv64-unknown-elf/11.1.0/../../../../riscv64-unknown-elf/bin/as -v -I base_lib --traditional-format -march=rv64imac -march=rv64imac -mabi=lp64 -o /tmp/cc4pRmao.o /tmp/ccpwBEao.s
GNU assembler version 2.37 (riscv64-unknown-elf) using BFD version (GNU Binutils) 2.37
COMPILER_PATH=/opt/riscv/libexec/gcc/riscv64-unknown-elf/11.1.0/:/opt/riscv/libexec/gcc/riscv64-unknown-elf/11.1.0/:/opt/riscv/libexec/gcc/riscv64-unknown-elf/:/opt/riscv/lib/gcc/riscv64-unknown-elf/11.1.0/:/opt/riscv/lib/gcc/riscv64-unknown-elf/:/opt/riscv/lib/gcc/riscv64-unknown-elf/11.1.0/../../../../riscv64-unknown-elf/bin/
LIBRARY_PATH=/opt/riscv/lib/gcc/riscv64-unknown-elf/11.1.0/:/opt/riscv/lib/gcc/riscv64-unknown-elf/11.1.0/../../../../riscv64-unknown-elf/lib/:/opt/riscv/riscv64-unknown-elf/lib/
COLLECT_GCC_OPTIONS='-I' 'base_lib' '-v' '-o' 'build/base_bin' '-mtune=rocket' '-march=rv64imac' '-mabi=lp64' '-march=rv64imac' '-dumpdir' 'build/base_bin.'
/opt/riscv/libexec/gcc/riscv64-unknown-elf/11.1.0/collect2 -plugin /opt/riscv/libexec/gcc/riscv64-unknown-elf/11.1.0/liblto_plugin.so -plugin-opt=/opt/riscv/libexec/gcc/riscv64-unknown-elf/11.1.0/lto-wrapper -plugin-opt=-fresolution=/tmp/ccQyuKYm.res -plugin-opt=-pass-through=-lgcc -plugin-opt=-pass-through=-lc -plugin-opt=-pass-through=-lgloss -plugin-opt=-pass-through=-lgcc --sysroot=/opt/riscv/riscv64-unknown-elf -melf64lriscv -o build/base_bin /opt/riscv/lib/gcc/riscv64-unknown-elf/11.1.0/../../../../riscv64-unknown-elf/lib/crt0.o /opt/riscv/lib/gcc/riscv64-unknown-elf/11.1.0/crtbegin.o -L/opt/riscv/lib/gcc/riscv64-unknown-elf/11.1.0 -L/opt/riscv/lib/gcc/riscv64-unknown-elf/11.1.0/../../../../riscv64-unknown-elf/lib -L/opt/riscv/riscv64-unknown-elf/lib /tmp/cc4pRmao.o base_lib/target/riscv64imac-unknown-none-elf/release/libbase_lib.a -lstdc++ -lm -lgcc --start-group -lc -lgloss --end-group -lgcc /opt/riscv/lib/gcc/riscv64-unknown-elf/11.1.0/crtend.o
/opt/riscv/lib/gcc/riscv64-unknown-elf/11.1.0/../../../../riscv64-unknown-elf/bin/ld: /tmp/cc4pRmao.o: in function `.L0 ':
main.c:(.text+0xa): undefined reference to `echo(unsigned int)'
collect2: error: ld returned 1 exit status
make: *** [Makefile:5: build/base_bin] Error 1
Thanks for any help.

Answer 1

Adding extern "C" in the header file will work, more details see What is the effect of extern "C" in C++? .
related to https://github.com/riscv-collab/riscv-gnu-toolchain/issues/1021.
Thanks for everyone helped me.