Problem cross-compiling trivial example with gcc when using hard float

问题

When I try to compile a trivial example test.c

int main () {
  return 0;
}

for a cortex m7 target with hard float ABI by using the following invocation

arm-none-eabi-gcc -mcpu=cortex-m7 -mfpu=fpv5-d16 -mfloat-abi=hard --specs=nosys.specs test.c

I get this error:

/usr/lib/gcc/arm-none-eabi/6.3.1/../../../arm-none-eabi/bin/ld: error: /usr/lib/gcc/arm-none-eabi/6.3.1/../../../arm-none-eabi/lib/crt0.o: Conflicting CPU architectures 13/1
/usr/lib/gcc/arm-none-eabi/6.3.1/../../../arm-none-eabi/bin/ld: failed to merge target specific data of file /usr/lib/gcc/arm-none-eabi/6.3.1/../../../arm-none-eabi/lib/crt0.o
/usr/lib/gcc/arm-none-eabi/6.3.1/../../../arm-none-eabi/bin/ld: error: a.out uses VFP register arguments, /usr/lib/gcc/arm-none-eabi/6.3.1/../../../arm-none-eabi/lib/libc.a(lib_a-atexit.o) does not
[snip]
/usr/lib/gcc/arm-none-eabi/6.3.1/../../../arm-none-eabi/bin/ld: failed to merge target specific data of file /usr/lib/gcc/arm-none-eabi/6.3.1/../../../arm-none-eabi/lib/libnosys.a(_exit.o)
collect2: error: ld returned 1 exit status

So the issue is that gcc is linking to the wrong libc.a. If I use the argument print-multi-directory, it would appear that my version of arm-none-eabi-gcc should support this architecture:

$ arm-none-eabi-gcc -mcpu=cortex-m7 -mfpu=fpv5-d16 -mfloat-abi=hard --specs=nosys.specs --print-multi-directory
thumb/v7e-m/fpv5/hard

And I can list the different versions of libc.a that are provided by arm-none-eabi-gcc:

$ find /usr/lib/arm-none-eabi/ -name libc.a
/usr/lib/arm-none-eabi/newlib/armv7e-m/libc.a
/usr/lib/arm-none-eabi/newlib/armv7e-m/fpu/fpv5-sp-d16/libc.a
/usr/lib/arm-none-eabi/newlib/armv7e-m/fpu/libc.a
/usr/lib/arm-none-eabi/newlib/armv7e-m/fpu/fpv5-d16/libc.a
/usr/lib/arm-none-eabi/newlib/armv7e-m/softfp/fpv5-sp-d16/libc.a
/usr/lib/arm-none-eabi/newlib/armv7e-m/softfp/libc.a
/usr/lib/arm-none-eabi/newlib/armv7e-m/softfp/fpv5-d16/libc.a
/usr/lib/arm-none-eabi/newlib/libc.a
/usr/lib/arm-none-eabi/newlib/armv6-m/libc.a
/usr/lib/arm-none-eabi/newlib/fpu/libc.a
/usr/lib/arm-none-eabi/newlib/thumb/libc.a
/usr/lib/arm-none-eabi/newlib/armv7-m/libc.a

So it looks like there is a version of libc.a compiled for my desired architecture, but gcc isn't linking against it. How can I get gcc to link against the correct version of libc.a?

I'm using arm-none-eabi-gcc version 6.3.1 provided by the gcc-arm-none-eabi package for Ubuntu 18.04.

来源：https://stackoverflow.com/questions/54288801/problem-cross-compiling-trivial-example-with-gcc-when-using-hard-float

标签

gcc

arm

cross-compiling

cortex-m