Multiple definitions of functions between libc.a and libc_nano.a while using nano.specs

Question

I am building a project for an STM32 microcontroller, and am including a .cpp file with some structures from the standard C++ library, such as std::vector, std::string etc. I'm not using std::cout or std::malloc. I need to use the reduced C/C++ library and am passing the -specs=nano.specs flag to the linker. I'm using arm-none-eabi cross-compiling tools to compile and link, and am using cmake to generate build files, and ninja to build.

I keep getting a linker error that says (for example),

/usr/local/gcc-arm-none-eabi-9-2020-q2-update/bin/../lib/gcc/arm-none-eabi/9.3.1/../../../../arm-none-eabi/bin/ld: /usr/local/gcc-arm-none-eabi-9-2020-q2-update/bin/../lib/gcc/arm-none-eabi/9.3.1/../../../../arm-none-eabi/lib/thumb/v7e-m+fp/hard/libc_nano.a(lib_a-findfp.o): in function `__sinit_lock_release':

findfp.c:(.text.__sinit_lock_release+0x0): multiple definition of `__sinit_lock_release'; /usr/local/gcc-arm-none-eabi-9-2020-q2-update/bin/../lib/gcc/arm-none-eabi/9.3.1/../../../../arm-none-eabi/lib/thumb/v7e-m+fp/hard/libc.a(lib_a-findfp.o):findfp.c:(.text.__sinit_lock_release+0x0): first defined here

1. I am a little confused about this error since I thought that the specs=nano.specs flag replaces libc.a with libc_nano.a, but here it looks like both libraries are being used and some of the functions are redefined in libc_nano.a.

2. If I use the -nostdlibs flag, I get undefined reference to errors such as:

/usr/local/gcc-arm-none-eabi-9-2020-q2-update/bin/../lib/gcc/arm-none-eabi/9.3.1/../../../../arm-none-eabi/bin/ld: CMakeFiles/WM_MainMicro.elf.dir/Core/Src/Components/message_table.cpp.obj: in function `std::vector<_app_msg, std::allocator<_app_msg> >::_M_check_len(unsigned int, char const*) const':
/usr/local/gcc-arm-none-eabi-9-2020-q2-update/arm-none-eabi/include/c++/9.3.1/bits/stl_vector.h:1756: undefined reference to `std::__throw_length_error(char const*)'
/usr/local/gcc-arm-none-eabi-9-2020-q2-update/bin/../lib/gcc/arm-none-eabi/9.3.1/../../../../arm-none-eabi/bin/ld: CMakeFiles/WM_MainMicro.elf.dir/Core/Src/Components/message_table.cpp.obj: in function `__gnu_cxx::new_allocator<_app_msg>::allocate(unsigned int, void const*)':

3. If I don't use nano.specs, my elf file is too large for the available Flash. (Which is why I want to use the reduced C/C++ library in the first place)

4. I found a flag called -allow-multiple-definitions which allows to me to compile without issues. From what I found in the documentation, this means that the linker will allow multiple definitions of a symbol, and will use first defined symbol. Does this mean that the linker will use the symbol from the library that's linked first? If so, which symbol will it use between the one from libc.a and libc_nano.a? (Considering that libc.a seems to be included by default)

Edit: Posting the entire linker error here:

/usr/local/gcc-arm-none-eabi-9-2020-q2-update/bin/../lib/gcc/arm-none-eabi/9.3.1/../../../../arm-none-eabi/bin/ld: /usr/local/gcc-arm-none-eabi-9-2020-q2-update/bin/../lib/gcc/arm-none-eabi/9.3.1/../../../../arm-none-eabi/lib/thumb/v7e-m+fp/hard/libc_nano.a(lib_a-findfp.o): in function `_cleanup_r':
findfp.c:(.text._cleanup_r+0x0): multiple definition of `_cleanup_r'; /usr/local/gcc-arm-none-eabi-9-2020-q2-update/bin/../lib/gcc/arm-none-eabi/9.3.1/../../../../arm-none-eabi/lib/thumb/v7e-m+fp/hard/libc.a(lib_a-findfp.o):findfp.c:(.text._cleanup_r+0x0): first defined here
/usr/local/gcc-arm-none-eabi-9-2020-q2-update/bin/../lib/gcc/arm-none-eabi/9.3.1/../../../../arm-none-eabi/bin/ld: /usr/local/gcc-arm-none-eabi-9-2020-q2-update/bin/../lib/gcc/arm-none-eabi/9.3.1/../../../../arm-none-eabi/lib/thumb/v7e-m+fp/hard/libc_nano.a(lib_a-findfp.o): in function `__sfmoreglue':
findfp.c:(.text.__sfmoreglue+0x0): multiple definition of `__sfmoreglue'; /usr/local/gcc-arm-none-eabi-9-2020-q2-update/bin/../lib/gcc/arm-none-eabi/9.3.1/../../../../arm-none-eabi/lib/thumb/v7e-m+fp/hard/libc.a(lib_a-findfp.o):findfp.c:(.text.__sfmoreglue+0x0): first defined here
/usr/local/gcc-arm-none-eabi-9-2020-q2-update/bin/../lib/gcc/arm-none-eabi/9.3.1/../../../../arm-none-eabi/bin/ld: /usr/local/gcc-arm-none-eabi-9-2020-q2-update/bin/../lib/gcc/arm-none-eabi/9.3.1/../../../../arm-none-eabi/lib/thumb/v7e-m+fp/hard/libc_nano.a(lib_a-findfp.o): in function `_cleanup':
findfp.c:(.text._cleanup+0x0): multiple definition of `_cleanup'; /usr/local/gcc-arm-none-eabi-9-2020-q2-update/bin/../lib/gcc/arm-none-eabi/9.3.1/../../../../arm-none-eabi/lib/thumb/v7e-m+fp/hard/libc.a(lib_a-findfp.o):findfp.c:(.text._cleanup+0x0): first defined here
/usr/local/gcc-arm-none-eabi-9-2020-q2-update/bin/../lib/gcc/arm-none-eabi/9.3.1/../../../../arm-none-eabi/bin/ld: /usr/local/gcc-arm-none-eabi-9-2020-q2-update/bin/../lib/gcc/arm-none-eabi/9.3.1/../../../../arm-none-eabi/lib/thumb/v7e-m+fp/hard/libc_nano.a(lib_a-findfp.o): in function `__sfp_lock_acquire':
findfp.c:(.text.__sfp_lock_acquire+0x0): multiple definition of `__sfp_lock_acquire'; /usr/local/gcc-arm-none-eabi-9-2020-q2-update/bin/../lib/gcc/arm-none-eabi/9.3.1/../../../../arm-none-eabi/lib/thumb/v7e-m+fp/hard/libc.a(lib_a-findfp.o):findfp.c:(.text.__sfp_lock_acquire+0x0): first defined here
/usr/local/gcc-arm-none-eabi-9-2020-q2-update/bin/../lib/gcc/arm-none-eabi/9.3.1/../../../../arm-none-eabi/bin/ld: /usr/local/gcc-arm-none-eabi-9-2020-q2-update/bin/../lib/gcc/arm-none-eabi/9.3.1/../../../../arm-none-eabi/lib/thumb/v7e-m+fp/hard/libc_nano.a(lib_a-findfp.o): in function `__sfp_lock_release':
findfp.c:(.text.__sfp_lock_release+0x0): multiple definition of `__sfp_lock_release'; /usr/local/gcc-arm-none-eabi-9-2020-q2-update/bin/../lib/gcc/arm-none-eabi/9.3.1/../../../../arm-none-eabi/lib/thumb/v7e-m+fp/hard/libc.a(lib_a-findfp.o):findfp.c:(.text.__sfp_lock_release+0x0): first defined here
/usr/local/gcc-arm-none-eabi-9-2020-q2-update/bin/../lib/gcc/arm-none-eabi/9.3.1/../../../../arm-none-eabi/bin/ld: /usr/local/gcc-arm-none-eabi-9-2020-q2-update/bin/../lib/gcc/arm-none-eabi/9.3.1/../../../../arm-none-eabi/lib/thumb/v7e-m+fp/hard/libc_nano.a(lib_a-findfp.o): in function `__sinit_lock_acquire':
findfp.c:(.text.__sinit_lock_acquire+0x0): multiple definition of `__sinit_lock_acquire'; /usr/local/gcc-arm-none-eabi-9-2020-q2-update/bin/../lib/gcc/arm-none-eabi/9.3.1/../../../../arm-none-eabi/lib/thumb/v7e-m+fp/hard/libc.a(lib_a-findfp.o):findfp.c:(.text.__sinit_lock_acquire+0x0): first defined here
/usr/local/gcc-arm-none-eabi-9-2020-q2-update/bin/../lib/gcc/arm-none-eabi/9.3.1/../../../../arm-none-eabi/bin/ld: /usr/local/gcc-arm-none-eabi-9-2020-q2-update/bin/../lib/gcc/arm-none-eabi/9.3.1/../../../../arm-none-eabi/lib/thumb/v7e-m+fp/hard/libc_nano.a(lib_a-findfp.o): in function `__sinit_lock_release':
findfp.c:(.text.__sinit_lock_release+0x0): multiple definition of `__sinit_lock_release'; /usr/local/gcc-arm-none-eabi-9-2020-q2-update/bin/../lib/gcc/arm-none-eabi/9.3.1/../../../../arm-none-eabi/lib/thumb/v7e-m+fp/hard/libc.a(lib_a-findfp.o):findfp.c:(.text.__sinit_lock_release+0x0): first defined here
/usr/local/gcc-arm-none-eabi-9-2020-q2-update/bin/../lib/gcc/arm-none-eabi/9.3.1/../../../../arm-none-eabi/bin/ld: /usr/local/gcc-arm-none-eabi-9-2020-q2-update/bin/../lib/gcc/arm-none-eabi/9.3.1/../../../../arm-none-eabi/lib/thumb/v7e-m+fp/hard/libc_nano.a(lib_a-findfp.o): in function `__sinit':
findfp.c:(.text.__sinit+0x0): multiple definition of `__sinit'; /usr/local/gcc-arm-none-eabi-9-2020-q2-update/bin/../lib/gcc/arm-none-eabi/9.3.1/../../../../arm-none-eabi/lib/thumb/v7e-m+fp/hard/libc.a(lib_a-findfp.o):findfp.c:(.text.__sinit+0x0): first defined here
/usr/local/gcc-arm-none-eabi-9-2020-q2-update/bin/../lib/gcc/arm-none-eabi/9.3.1/../../../../arm-none-eabi/bin/ld: /usr/local/gcc-arm-none-eabi-9-2020-q2-update/bin/../lib/gcc/arm-none-eabi/9.3.1/../../../../arm-none-eabi/lib/thumb/v7e-m+fp/hard/libc_nano.a(lib_a-findfp.o): in function `__sfp':
findfp.c:(.text.__sfp+0x0): multiple definition of `__sfp'; /usr/local/gcc-arm-none-eabi-9-2020-q2-update/bin/../lib/gcc/arm-none-eabi/9.3.1/../../../../arm-none-eabi/lib/thumb/v7e-m+fp/hard/libc.a(lib_a-findfp.o):findfp.c:(.text.__sfp+0x0): first defined here
/usr/local/gcc-arm-none-eabi-9-2020-q2-update/bin/../lib/gcc/arm-none-eabi/9.3.1/../../../../arm-none-eabi/bin/ld: /usr/local/gcc-arm-none-eabi-9-2020-q2-update/bin/../lib/gcc/arm-none-eabi/9.3.1/../../../../arm-none-eabi/lib/thumb/v7e-m+fp/hard/libc_nano.a(lib_a-findfp.o): in function `__fp_lock_all':
findfp.c:(.text.__fp_lock_all+0x0): multiple definition of `__fp_lock_all'; /usr/local/gcc-arm-none-eabi-9-2020-q2-update/bin/../lib/gcc/arm-none-eabi/9.3.1/../../../../arm-none-eabi/lib/thumb/v7e-m+fp/hard/libc.a(lib_a-findfp.o):findfp.c:(.text.__fp_lock_all+0x0): first defined here
/usr/local/gcc-arm-none-eabi-9-2020-q2-update/bin/../lib/gcc/arm-none-eabi/9.3.1/../../../../arm-none-eabi/bin/ld: /usr/local/gcc-arm-none-eabi-9-2020-q2-update/bin/../lib/gcc/arm-none-eabi/9.3.1/../../../../arm-none-eabi/lib/thumb/v7e-m+fp/hard/libc_nano.a(lib_a-findfp.o): in function `__fp_unlock_all':
findfp.c:(.text.__fp_unlock_all+0x0): multiple definition of `__fp_unlock_all'; /usr/local/gcc-arm-none-eabi-9-2020-q2-update/bin/../lib/gcc/arm-none-eabi/9.3.1/../../../../arm-none-eabi/lib/thumb/v7e-m+fp/hard/libc.a(lib_a-findfp.o):findfp.c:(.text.__fp_unlock_all+0x0): first defined here
/usr/local/gcc-arm-none-eabi-9-2020-q2-update/bin/../lib/gcc/arm-none-eabi/9.3.1/../../../../arm-none-eabi/bin/ld: /usr/local/gcc-arm-none-eabi-9-2020-q2-update/bin/../lib/gcc/arm-none-eabi/9.3.1/../../../../arm-none-eabi/lib/thumb/v7e-m+fp/hard/libc_nano.a(lib_a-snprintf.o): in function `_snprintf_r':
snprintf.c:(.text._snprintf_r+0x0): multiple definition of `_snprintf_r'; /usr/local/gcc-arm-none-eabi-9-2020-q2-update/bin/../lib/gcc/arm-none-eabi/9.3.1/../../../../arm-none-eabi/lib/thumb/v7e-m+fp/hard/libc.a(lib_a-snprintf.o):snprintf.c:(.text._snprintf_r+0x0): first defined here
/usr/local/gcc-arm-none-eabi-9-2020-q2-update/bin/../lib/gcc/arm-none-eabi/9.3.1/../../../../arm-none-eabi/bin/ld: /usr/local/gcc-arm-none-eabi-9-2020-q2-update/bin/../lib/gcc/arm-none-eabi/9.3.1/../../../../arm-none-eabi/lib/thumb/v7e-m+fp/hard/libc_nano.a(lib_a-snprintf.o): in function `snprintf':
snprintf.c:(.text.snprintf+0x0): multiple definition of `snprintf'; /usr/local/gcc-arm-none-eabi-9-2020-q2-update/bin/../lib/gcc/arm-none-eabi/9.3.1/../../../../arm-none-eabi/lib/thumb/v7e-m+fp/hard/libc.a(lib_a-snprintf.o):snprintf.c:(.text.snprintf+0x0): first defined here
/usr/local/gcc-arm-none-eabi-9-2020-q2-update/bin/../lib/gcc/arm-none-eabi/9.3.1/../../../../arm-none-eabi/bin/ld: /usr/local/gcc-arm-none-eabi-9-2020-q2-update/bin/../lib/gcc/arm-none-eabi/9.3.1/../../../../arm-none-eabi/lib/thumb/v7e-m+fp/hard/libc_nano.a(lib_a-nano-svfprintf.o): in function `__ssprint_r':
nano-vfprintf.c:(.text.__ssprint_r+0x0): multiple definition of `__ssprint_r'; /usr/local/gcc-arm-none-eabi-9-2020-q2-update/bin/../lib/gcc/arm-none-eabi/9.3.1/../../../../arm-none-eabi/lib/thumb/v7e-m+fp/hard/libc.a(lib_a-svfiprintf.o):vfprintf.c:(.text.__ssprint_r+0x0): first defined here
/usr/local/gcc-arm-none-eabi-9-2020-q2-update/bin/../lib/gcc/arm-none-eabi/9.3.1/../../../../arm-none-eabi/bin/ld: /usr/local/gcc-arm-none-eabi-9-2020-q2-update/bin/../lib/gcc/arm-none-eabi/9.3.1/../../../../arm-none-eabi/lib/thumb/v7e-m+fp/hard/libc_nano.a(lib_a-nano-svfprintf.o): in function `_svfprintf_r':
nano-vfprintf.c:(.text._svfprintf_r+0x0): multiple definition of `_svfprintf_r'; /usr/local/gcc-arm-none-eabi-9-2020-q2-update/bin/../lib/gcc/arm-none-eabi/9.3.1/../../../../arm-none-eabi/lib/thumb/v7e-m+fp/hard/libc.a(lib_a-svfprintf.o):vfprintf.c:(.text._svfprintf_r+0x0): first defined here
/usr/local/gcc-arm-none-eabi-9-2020-q2-update/bin/../lib/gcc/arm-none-eabi/9.3.1/../../../../arm-none-eabi/bin/ld: /usr/local/gcc-arm-none-eabi-9-2020-q2-update/bin/../lib/gcc/arm-none-eabi/9.3.1/../../../../arm-none-eabi/lib/thumb/v7e-m+fp/hard/libc_nano.a(lib_a-nano-svfprintf.o): in function `_svfprintf_r':
nano-vfprintf.c:(.text._svfprintf_r+0x0): multiple definition of `_svfiprintf_r'; /usr/local/gcc-arm-none-eabi-9-2020-q2-update/bin/../lib/gcc/arm-none-eabi/9.3.1/../../../../arm-none-eabi/lib/thumb/v7e-m+fp/hard/libc.a(lib_a-svfiprintf.o):vfprintf.c:(.text._svfiprintf_r+0x0): first defined here

Answer 1

You can try the -nolibc option instead of -nostdlibs. I think the issue is that with the original option it would not use both the standard C/C++ libraries. In your case you only want to replace libc only

-nolibc

Do not use the C library or system libraries tightly coupled with it when linking. Still link with the startup files, libgcc or toolchain provided language support libraries such as libgnat, libgfortran or libstdc++ unless options preventing their inclusion are used as well. This typically removes -lc from the link command line, as well as system libraries that normally go with it and become meaningless when absence of a C library is assumed, for example -lpthread or -lm in some configurations. This is intended for bare-board targets when there is indeed no C library