main.c.o uses VFP register arguments, a.out does not

Question

I have a main.c that is being compiled like so:

arm-none-eabi-gcc -mcpu=cortex-a9 -mfpu=vfpv3 -mfloat-abi=hard -o CMakeFiles/lab1.elf.dir/main.c.o -c main.c

The output of readelf -A main.c.o:

Attribute Section: aeabi
File Attributes
  Tag_CPU_name: "7-A"
  Tag_CPU_arch: v7
  Tag_CPU_arch_profile: Application
  Tag_ARM_ISA_use: Yes
  Tag_THUMB_ISA_use: Thumb-2
  Tag_FP_arch: VFPv3
  Tag_ABI_PCS_wchar_t: 4
  Tag_ABI_FP_denormal: Needed
  Tag_ABI_FP_exceptions: Needed
  Tag_ABI_FP_number_model: IEEE 754
  Tag_ABI_align_needed: 8-byte
  Tag_ABI_align_preserved: 8-byte, except leaf SP
  Tag_ABI_enum_size: small
  Tag_ABI_VFP_args: VFP registers
  Tag_ABI_optimization_goals: Aggressive Debug
  Tag_CPU_unaligned_access: v6
  Tag_MPextension_use: Allowed
  Tag_Virtualization_use: TrustZone

I then want to link this file with some other libraries I have (these are C++ libraries so I am using the g++ linker). I keep getting an error that the executable isn't using VFP arguments, despite the command line options to enable them:

arm-none-eabi-g++ -mcpu=cortex-a9 -mfpu=vfpv3 -mfloat-abi=hard  CMakeFiles/lab1.elf.dir/main.c.o

This is the output:

(Yes, there are lots of other issues with missing libraries, etc, but I'm trying to reduce this down to a simple example).

(Also, this worked fine in GCC 6.3.1, it's only broken now that I'm trying in 9.2.1)

/usr/lib/gcc/arm-none-eabi/9.2.1/../../../arm-none-eabi/bin/ld: error: CMakeFiles/lab1.elf.dir/main.c.o uses VFP register arguments, a.out does not
/usr/lib/gcc/arm-none-eabi/9.2.1/../../../arm-none-eabi/bin/ld: failed to merge target specific data of file CMakeFiles/lab1.elf.dir/main.c.o
/usr/lib/gcc/arm-none-eabi/9.2.1/../../../arm-none-eabi/bin/ld: CMakeFiles/lab1.elf.dir/main.c.o: in function `main':
main.c:(.text+0x8): undefined reference to `display_init'
/usr/lib/gcc/arm-none-eabi/9.2.1/../../../arm-none-eabi/bin/ld: main.c:(.text+0x10): undefined reference to `display_fillScreen'
/usr/lib/gcc/arm-none-eabi/9.2.1/../../../arm-none-eabi/bin/ld: main.c:(.text+0x1c): undefined reference to `display_setCursor'
/usr/lib/gcc/arm-none-eabi/9.2.1/../../../arm-none-eabi/bin/ld: main.c:(.text+0x24): undefined reference to `display_setTextColor'
/usr/lib/gcc/arm-none-eabi/9.2.1/../../../arm-none-eabi/bin/ld: main.c:(.text+0x2c): undefined reference to `display_setTextSize'
/usr/lib/gcc/arm-none-eabi/9.2.1/../../../arm-none-eabi/bin/ld: main.c:(.text+0x38): undefined reference to `display_println'
/usr/lib/gcc/arm-none-eabi/9.2.1/../../../arm-none-eabi/bin/ld: /usr/lib/gcc/arm-none-eabi/9.2.1/../../../arm-none-eabi/lib/libc.a(lib_a-exit.o): in function `exit':
/build/newlib-CVVEyx/newlib-3.3.0/build/arm-none-eabi/newlib/libc/stdlib/../../../../../newlib/libc/stdlib/exit.c:64: undefined reference to `_exit'
/usr/lib/gcc/arm-none-eabi/9.2.1/../../../arm-none-eabi/bin/ld: /usr/lib/gcc/arm-none-eabi/9.2.1/../../../arm-none-eabi/lib/libc.a(lib_a-sbrkr.o): in function `_sbrk_r':
/build/newlib-CVVEyx/newlib-3.3.0/build/arm-none-eabi/newlib/libc/reent/../../../../../newlib/libc/reent/sbrkr.c:51: undefined reference to `_sbrk'
/usr/lib/gcc/arm-none-eabi/9.2.1/../../../arm-none-eabi/bin/ld: /usr/lib/gcc/arm-none-eabi/9.2.1/../../../arm-none-eabi/lib/libc.a(lib_a-writer.o): in function `_write_r':
/build/newlib-CVVEyx/newlib-3.3.0/build/arm-none-eabi/newlib/libc/reent/../../../../../newlib/libc/reent/writer.c:49: undefined reference to `_write'
/usr/lib/gcc/arm-none-eabi/9.2.1/../../../arm-none-eabi/bin/ld: /usr/lib/gcc/arm-none-eabi/9.2.1/../../../arm-none-eabi/lib/libc.a(lib_a-closer.o): in function `_close_r':
/build/newlib-CVVEyx/newlib-3.3.0/build/arm-none-eabi/newlib/libc/reent/../../../../../newlib/libc/reent/closer.c:47: undefined reference to `_close'
/usr/lib/gcc/arm-none-eabi/9.2.1/../../../arm-none-eabi/bin/ld: /usr/lib/gcc/arm-none-eabi/9.2.1/../../../arm-none-eabi/lib/libc.a(lib_a-fstatr.o): in function `_fstat_r':
/build/newlib-CVVEyx/newlib-3.3.0/build/arm-none-eabi/newlib/libc/reent/../../../../../newlib/libc/reent/fstatr.c:55: undefined reference to `_fstat'
/usr/lib/gcc/arm-none-eabi/9.2.1/../../../arm-none-eabi/bin/ld: /usr/lib/gcc/arm-none-eabi/9.2.1/../../../arm-none-eabi/lib/libc.a(lib_a-isattyr.o): in function `_isatty_r':
/build/newlib-CVVEyx/newlib-3.3.0/build/arm-none-eabi/newlib/libc/reent/../../../../../newlib/libc/reent/isattyr.c:52: undefined reference to `_isatty'
/usr/lib/gcc/arm-none-eabi/9.2.1/../../../arm-none-eabi/bin/ld: /usr/lib/gcc/arm-none-eabi/9.2.1/../../../arm-none-eabi/lib/libc.a(lib_a-lseekr.o): in function `_lseek_r':
/build/newlib-CVVEyx/newlib-3.3.0/build/arm-none-eabi/newlib/libc/reent/../../../../../newlib/libc/reent/lseekr.c:49: undefined reference to `_lseek'
/usr/lib/gcc/arm-none-eabi/9.2.1/../../../arm-none-eabi/bin/ld: /usr/lib/gcc/arm-none-eabi/9.2.1/../../../arm-none-eabi/lib/libc.a(lib_a-readr.o): in function `_read_r':
/build/newlib-CVVEyx/newlib-3.3.0/build/arm-none-eabi/newlib/libc/reent/../../../../../newlib/libc/reent/readr.c:49: undefined reference to `_read'
/usr/lib/gcc/arm-none-eabi/9.2.1/../../../arm-none-eabi/bin/ld: /usr/lib/gcc/arm-none-eabi/9.2.1/../../../arm-none-eabi/lib/libc.a(lib_a-abort.o): in function `abort':
/build/newlib-CVVEyx/newlib-3.3.0/build/arm-none-eabi/newlib/libc/stdlib/../../../../../newlib/libc/stdlib/abort.c:59: undefined reference to `_exit'
/usr/lib/gcc/arm-none-eabi/9.2.1/../../../arm-none-eabi/bin/ld: /usr/lib/gcc/arm-none-eabi/9.2.1/../../../arm-none-eabi/lib/libc.a(lib_a-signalr.o): in function `_kill_r':
/build/newlib-CVVEyx/newlib-3.3.0/build/arm-none-eabi/newlib/libc/reent/../../../../../newlib/libc/reent/signalr.c:53: undefined reference to `_kill'
/usr/lib/gcc/arm-none-eabi/9.2.1/../../../arm-none-eabi/bin/ld: /usr/lib/gcc/arm-none-eabi/9.2.1/../../../arm-none-eabi/lib/libc.a(lib_a-signalr.o): in function `_getpid_r':
/build/newlib-CVVEyx/newlib-3.3.0/build/arm-none-eabi/newlib/libc/reent/../../../../../newlib/libc/reent/signalr.c:83: undefined reference to `_getpid'
collect2: error: ld returned 1 exit status

Generally you have to compile all your libraries with the same ABI. — user253751, Aug 14 '20 at 18:23
Yes, I am specifying `-mcpu=cortex-a9 -mfpu=vfpv3 -mfloat-abi=hard` to both the compile and link step. I'm not linking in any libraries yet, but am still getting the error. The error suggests that I'm not proving `-mfloat-abi=hard` to the linker that is generating a.out, but I am. That's what's confusing. — jgoeders, Aug 14 '20 at 19:16
You are linking the standard C library (newlib libc) by default. — user253751, Aug 14 '20 at 19:16
Is there some way to tell which libc is being used by arm-none-eabi-g++, so that I can check if it is compiled with hard float? — jgoeders, Aug 14 '20 at 19:25
Well, the error messages *literally tell you* which library has problems. And I'll point out that if it was hard-float, everything would be called eabihf, not eabi — user253751, Aug 14 '20 at 19:48

score 1 · Answer 1 · answered Apr 05 '21 at 23:30

In case somebody in the futures stumbles upon this topic and is looking for answers:

I had to check if -mfloat-abi=hard was set for GCC G++ and Linker. But because hardware is selected, I had to ALSO check if -mfpu=XXX was set (which was not for some obscure reason)

score 0 · Answer 2 · answered Aug 14 '20 at 21:47

I believe this is a similar problem to that discussed here: Problem cross-compiling trivial example with gcc when using hard float

It seems that the wrong libc version is being linked in, despite the -mcpu=cortex-a9 -mfpu=vfpv3 -mfloat-abi=hard options given to the linker.

I was able to fix this by using -march=armv7-a instead of -mcpu=cortex-a9, as suggested in one of the comments on that page.

main.c.o uses VFP register arguments, a.out does not

2 Answers2