Missing something in arm g++

I installed the CodeSourcery g++ toolchain and tried to compile a simple hello world program:

#include <iostream>

using namespace std;

int main()
{
    cout << "Hello World" << endl;
    return 0;
}

And got a lot of errors from the linker

$ arm-none-eabi-g++ helloworld.cpp -o helloworld.exe
bin/ld: warning: cannot find entry symbol _start; defaulting to 0000000000008018
lib/libc.a(lib_a-abort.o): In function `abort':
abort.c:(开发者_运维知识库.text.abort+0x10): undefined reference to `_exit'
lib/libc.a(lib_a-fstatr.o): In function `_fstat_r':
fstatr.c:(.text._fstat_r+0x1c): undefined reference to `_fstat'
lib/libc.a(lib_a-openr.o): In function `_open_r':
openr.c:(.text._open_r+0x20): undefined reference to `_open'
lib/libc.a(lib_a-sbrkr.o): In function `_sbrk_r':
sbrkr.c:(.text._sbrk_r+0x18): undefined reference to `_sbrk'
lib/libc.a(lib_a-signalr.o): In function `_kill_r':
signalr.c:(.text._kill_r+0x1c): undefined reference to `_kill'
lib/libc.a(lib_a-signalr.o): In function `_getpid_r':
signalr.c:(.text._getpid_r+0x4): undefined reference to `_getpid'
lib/libc.a(lib_a-writer.o): In function `_write_r':
writer.c:(.text._write_r+0x20): undefined reference to `_write'
lib/libc.a(lib_a-closer.o): In function `_close_r':
closer.c:(.text._close_r+0x18): undefined reference to `_close'
lib/libc.a(lib_a-isattyr.o): In function `_isatty_r':
isattyr.c:(.text._isatty_r+0x18): undefined reference to `_isatty'
lib/libc.a(lib_a-lseekr.o): In function `_lseek_r':
lseekr.c:(.text._lseek_r+0x20): undefined reference to `_lseek'
lib/libc.a(lib_a-readr.o): In function `_read_r':
readr.c:(.text._read_r+0x20): undefined reference to `_read'
collect2: ld returned 1 exit status

What library am I missing here?

---

The GCC toolchain is only half of what you need to create a working executable*. The other half is the runtime library. The runtime includes crt0.o, which contains the entry point (the code that calls main()), and generally a libc that contains the standard C functions (strcmp(), memcpy(), etc) as well as the system calls (open(), read(), and others). You need to find a source for these. If you're targeting an embedded Linux or BSD machine, you'll have to find out what libc your target is using. It's probably either GNU libc, BSD libc, newlib, or uclibc. You can get these and build them yourself, or they may be available already with your OS.

*unless you're building a freestanding binary, but this doesn't look to be what you're doing.

---

Basing on the cross compiler it appears that end target is bare metal. The default gcc libraries (OS dependent) will not work here. You can use the NewlibC or NewlibC-Nano. This generally will be shipped along with the cross compiler tool chain.

Look for lib folder which has precompiled NewlibC.

Once that is done,

This statement might help you to an extent.

arm-none-eabi-gcc --specs=rdimon.specs \
         -Wl,--start-group -lgcc -lc -lc -lm -lrdimon -Wl,--end-group $(OTHER_OPTIONS)

Don't forget to provide the path of looking the libraries -L(path).

---

I had this same problem.

It turns out there are a handful of options you can send to the linker to make it start working, but the one that had the least splash damage in my code base was

-nostartfiles