ARM compilation error, VFP registered used by exec

Question

I have been having this problem for the last few days and I can't get my head around what is really happening here, or what is the problem.

I have a makefile with these flags:

CC = arm-linux-gnueabihf-gcc-4.6
FLAGS = -O3 -march=armv7-a -mtune=cortex-a9 -mfpu=neon -ftree-vectorize -mfloat-abi=softfp -std=gnu99

I have a library in a .a file, which has some object files, all I need to do is link them in with my executable. I know the prototypes and all that, the only thing that complains is the following:

/usr/bin/ld: error: *EXECUTABLE* uses VFP register arguments, *OBJECTFILE* does not
/usr/bin/ld: failed to merge target specific data of file *OBJECTFILE*

When I don't use the -mfloat-abi=softfp, I get another error relating to floating point registers.

Does anyone have any idea what is causing this, and what I can do to fix this, such as making it so that my executable does not use Virtual Floating Point Register arguments?

x@x:~/Desktop/perf_test$ make
arm-linux-gnueabihf-gcc-4.6 -c -O3 -march=armv7-a -mtune=cortex-a9 -mfpu=neon -ftree-vectorize -std=gnu99 -mfloat-abi=softfp  perf_test.c ../baseline/util.c
arm-linux-gnueabihf-gcc-4.6 -o perf_test perf_test.o util.o  ../baseline/lib.a
/usr/bin/ld: error: perf_test uses VFP register arguments, perf_test.o does not
/usr/bin/ld: failed to merge target specific data of file perf_test.o
/usr/bin/ld: error: perf_test uses VFP register arguments, util.o does not
/usr/bin/ld: failed to merge target specific data of file util.o
/usr/bin/ld: error: perf_test uses VFP register arguments, ../baseline/lib.a(a.o) does not
/usr/bin/ld: failed to merge target specific data of file ../baseline/lib.a(a.o)
/usr/bin/ld: error: perf_test uses VFP register arguments, ../baseline/lib.a(b.o) does not
/usr/bin/ld: failed to merge target specific data of file ../baseline/lib.a(b.o)
/usr/bin/ld: error: perf_test uses VFP register arguments, ../baseline/lib.a(c.o) does not
/usr/bin/ld: failed to merge target specific data of file ../baseline/lib.a(c.o)
/usr/bin/ld: error: perf_test uses VFP register arguments, ../baseline/lib.a(d.o) does not
/usr/bin/ld: failed to merge target specific data of file ../baseline/lib.a(d.o)
/usr/bin/ld: error: perf_test uses VFP register arguments, ../baseline/lib.a(e.o) does not
/usr/bin/ld: failed to merge target specific data of file ../baseline/lib.a(e.o)
/usr/bin/ld: error: perf_test uses VFP register arguments, ../baseline/lib.a(f.o) does not
/usr/bin/ld: failed to merge target specific data of file ../baseline/lib.a(f.o)
collect2: ld returned 1 exit status
make: *** [perf_test] Error 1

Answer 1

Also the error can be solved by adding several flags, like -marm -mthumb-interwork. It was helpful for me to avoid this same error.

Answer 2

Use the same compiler options for linking also.

Example:

gcc  -mfloat-abi=hard fpu=neon -c -o test.cpp test.o
gcc  -mfloat-abi=hard fpu=neon -c test1.cpp test1.o
gcc test.o test1.o mfloat-abi=hard fpu=neon HardTest

Answer 3

This answer may appear at the surface to be unrelated, but there is an indirect cause of this error message.

First, the "Uses VFP register..." error message is directly caused from mixing mfloat-abi=soft and mfloat-abi=hard options within your build. This setting must be consistent for all objects that are to be linked. This fact is well covered in the other answers to this question.

The indirect cause of this error may be due to the Eclipse editor getting confused by a self-inflicted error in the project's ".cproject" file. The Eclipse editor frequently reswizzles file links and sometimes it breaks itself when you make changes to your directory structures or file locations. This can also affect the path settings to your gcc compiler - and only for a subset of your project's files. While I'm not yet sure of exactly what causes this failure, replacing the .cproject file with a backup copy corrected this problem for me. In my case I noticed .java.null.pointer errors after adding an include directory path and started receiving the "VFP register error" messages out of the blue. In the build log I noticed that a different path to the gcc compiler was being used for some of my sources that were local to the workspace, but not all of them!? The two gcc compilers were using different float settings for unknown reasons - hence the VFP register error.

I compared the .cproject settings with a older copy and observed differences in entries for the sources causing the trouble - even though the overriding of project settings was disabled. By replacing the .cproject file with the old version the problem went away, and I'm leaving this answer as a reminder of what happened.

Answer 4

Your target triplet indicates that your compiler is configured for the hard-float ABI. This means that the libgcc library will also be hardfp. The error message indicates that at least part of your system is using soft-float ABI.

If the compiler has multilib enabled (you can tell with -print-multi-lib) then you can use -mfloat-abi=softfp, but if not then that option won't help you much: gcc will happily generate softfp code, but then there'll be no compatible libgcc to link against.

Basically, hardfp and softfp are just not compatible. You need to get your whole system configured one way or the other.

EDIT: some distros are, or will be, "multiarch". If you have one of those then it's possible to install both ABIs at once, but that's done by doubling everything up -- the compatibility issues still exist.