Include C++ examples with and without standard library

[autrilla]

Hi! First of all thanks a lot for the work you've done to make it easy to get a fully functional ESP8266 toolchain. There's already an example for building a small project with exclusively C source files. Making it build C++ source files is relatively easy working from this example, as it works out of the box with the specified compiler and linker flags. However, if you want to use the C++ standard library at all, things get more complicated.

This is as far as I've got so far:

CC = xtensa-lx106-elf-gcc
CXX = xtensa-lx106-elf-g++
CFLAGS		= -I. -Os -g -O2 -Wall -Wpointer-arith -Wundef -Werror -Wl,-EL -fno-inline-functions -nostdlib -mlongcalls -mtext-section-literals  -D__ets__ -DICACHE_FLASH
CXXFLAGS	= $(CFLAGS) -fno-rtti -fno-exceptions -std=c++11
LDLIBS = -Wl,--start-group -lmain -lnet80211 -lwpa -llwip -lpp -lphy -lc -Wl,--end-group -lgcc -lstdc++
LDFLAGS = -Teagle.app.v6.ld

example-0x00000.bin: example
	esptool.py elf2image $^

example: example.o

example.o: example.cpp

flash: example-0x00000.bin
	esptool.py --port=/dev/tty.wchusbserial1420 write_flash --flash_mode dio 0 example-0x00000.bin 0x10000 example-0x10000.bin

clean:
	rm -f example example.o example-0x00000.bin example-0x10000.bin

But the linker fails:

❯ make flash
xtensa-lx106-elf-gcc -Teagle.app.v6.ld  example.o  -Wl,--start-group -lmain -lnet80211 -lwpa -llwip -lpp -lphy -lc -Wl,--end-group -lgcc -lstdc++ -o example
/Volumes/case-sensitive/esp-open-sdk/xtensa-lx106-elf/lib/gcc/xtensa-lx106-elf/4.8.5/../../../../xtensa-lx106-elf/bin/ld: cannot find crt1-sim.o: No such file or directory
/Volumes/case-sensitive/esp-open-sdk/xtensa-lx106-elf/lib/gcc/xtensa-lx106-elf/4.8.5/../../../../xtensa-lx106-elf/bin/ld: cannot find _vectors.o: No such file or directory
collect2: error: ld returned 1 exit status
make: *** [example] Error 1

Googling shows some people hitting similar issues, but I haven't been able to find a solution.

[jcmvbkbc]

ld: cannot find crt1-sim.o: No such file or directory
ld: cannot find _vectors.o: No such file or directory

Having -nostdlib in LDLIBS should fix that. Or you can try changes from PR #209

[autrilla]

Having -nostdlib in LDLIBS was one of the things I tried, and it indeed did not work:

❯ make                                                                       
xtensa-lx106-elf-gcc -Teagle.app.v6.ld -nostdlib  example.o  -Wl,--start-group -lmain -lnet80211 -lwpa -llwip -lpp -lphy -lc -Wl,--end-group -lgcc -lstdc++ -lsupc++ -nostdlib -o example
/Volumes/case-sensitive/esp-open-sdk/xtensa-lx106-elf/lib/gcc/xtensa-lx106-elf/4.8.5/../../../../xtensa-lx106-elf/lib/libstdc++.a(del_op.o):(.literal._ZdlPv+0x0): undefined reference to `free'
/Volumes/case-sensitive/esp-open-sdk/xtensa-lx106-elf/lib/gcc/xtensa-lx106-elf/4.8.5/../../../../xtensa-lx106-elf/lib/libstdc++.a(del_op.o): In function `operator delete(void*)':
/Volumes/case-sensitive/esp-open-sdk/crosstool-NG/.build/src/gcc-4.8.5/libstdc++-v3/libsupc++/del_op.cc:47: undefined reference to `free'
/Volumes/case-sensitive/esp-open-sdk/xtensa-lx106-elf/lib/gcc/xtensa-lx106-elf/4.8.5/../../../../xtensa-lx106-elf/lib/libstdc++.a(new_op.o):(.literal._Znwj+0x4): undefined reference to `abort'
/Volumes/case-sensitive/esp-open-sdk/xtensa-lx106-elf/lib/gcc/xtensa-lx106-elf/4.8.5/../../../../xtensa-lx106-elf/lib/libstdc++.a(new_op.o):(.literal._Znwj+0x8): undefined reference to `malloc'
/Volumes/case-sensitive/esp-open-sdk/xtensa-lx106-elf/lib/gcc/xtensa-lx106-elf/4.8.5/../../../../xtensa-lx106-elf/lib/libstdc++.a(new_op.o): In function `operator new(unsigned int)':
/Volumes/case-sensitive/esp-open-sdk/crosstool-NG/.build/src/gcc-4.8.5/libstdc++-v3/libsupc++/new_op.cc:56: undefined reference to `abort'
/Volumes/case-sensitive/esp-open-sdk/crosstool-NG/.build/src/gcc-4.8.5/libstdc++-v3/libsupc++/new_op.cc:58: undefined reference to `malloc'
collect2: error: ld returned 1 exit status
make: *** [example] Error 1

So it looks like it's missing a few symbols that are defined in the system libraries?

I'll give that PR a shot later, thanks for your help!

[jcmvbkbc]

del_op.cc:47: undefined reference to free' new_op.cc:56: undefined reference to abort'
new_op.cc:58: undefined reference to `malloc'

Oh, yes, right. You need something like the following in order to make libstdc++/libsupc++ happy:

void *operator new(size_t size)
{
   return os_malloc(size);
}
        
void *operator new[](size_t size)
{
   return os_malloc(size);
}

void operator delete(void * ptr)
{
   os_free(ptr);
}

void operator delete[](void * ptr)
{
   os_free(ptr);
}

extern "C" void __cxa_pure_virtual(void) __attribute__ ((__noreturn__));
extern "C" void __cxa_deleted_virtual(void) __attribute__ ((__noreturn__));
extern "C" void abort()
{
   while(true); // enter an infinite loop and get reset by the WDT
}
    
void __cxa_pure_virtual(void)
{
  abort();
}

void __cxa_deleted_virtual(void)
{
  abort();
}

I'll give that PR a shot later

Never mind, it won't fix the above missing symbols.