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Compiler: Linaro Tools - FPU library & CCS

Guy Mardiks
Genius 4135 points

Tool/software: TI C/C++ Compiler

Hello,

Using Linaro tools for the A15 on TDA2xx.

I would like your help in understanding the Linaro tools folder tree, specifically, how do i choose the proper FPU library.

on version 4_9_2015q3 there are several FPU folders containing FPU libraries (i.e. one under the gcc folder, one under lib, and under some architecture folders) - it is very confusing as to why all of these exist and how to know which is the correct one to choose (if need to choose at all - could it be it is internally being defined to be taken according to other configurations?)

In addition on a newer Linaro tools version, the FPU under the gcc folder no longer exist and in general the folder tree was changes so this adds up to the confusion of how to properly know what should be used and how.

Another issue is, i have tried installing the new CCS 9, on CCS 8 there was an automatic variable definition for CG_GCC_SEARCH_PATH , but on the new CCS 9 this does no longer exists. can you explain the difference ?

Thanks

Guy

  • 0
    Guru 92251 points

    Guy Mardiks said:
    In addition on a newer Linaro tools version, the FPU under the gcc folder no longer exist and in general the folder tree was changes so this adds up to the confusion of how to properly know what should be used and how.

    The GCC multilib is used to select the library to link, based upon the command line parameters. Using the -print-multi-lib option on different GCC ARM versions installed by CCS shows the following:

    ~/ti/ccs830/ccsv8/tools/compiler/gcc-arm-none-eabi-4_9-2015q3/bin/arm-none-eabi-gcc -print-multi-lib
.;
thumb;@mthumb
fpu;@mfloat-abi=hard
armv6-m;@mthumb@march=armv6s-m
armv7-m;@mthumb@march=armv7-m
armv7e-m;@mthumb@march=armv7e-m
armv7-ar/thumb;@mthumb@march=armv7
cortex-m7;@mthumb@mcpu=cortex-m7
armv7e-m/softfp;@mthumb@march=armv7e-m@mfloat-abi=softfp@mfpu=fpv4-sp-d16
armv7e-m/fpu;@mthumb@march=armv7e-m@mfloat-abi=hard@mfpu=fpv4-sp-d16
armv7-ar/thumb/softfp;@mthumb@march=armv7@mfloat-abi=softfp@mfpu=vfpv3-d16
armv7-ar/thumb/fpu;@mthumb@march=armv7@mfloat-abi=hard@mfpu=vfpv3-d16
cortex-m7/softfp/fpv5-sp-d16;@mthumb@mcpu=cortex-m7@mfloat-abi=softfp@mfpu=fpv5-sp-d16
cortex-m7/softfp/fpv5-d16;@mthumb@mcpu=cortex-m7@mfloat-abi=softfp@mfpu=fpv5-d16
cortex-m7/fpu/fpv5-sp-d16;@mthumb@mcpu=cortex-m7@mfloat-abi=hard@mfpu=fpv5-sp-d16
cortex-m7/fpu/fpv5-d16;@mthumb@mcpu=cortex-m7@mfloat-abi=hard@mfpu=fpv5-d16
    ~/ti/ccs830/ccsv8/tools/compiler/gcc-arm-none-eabi-6-2017-q1-update/bin/arm-none-eabi-gcc -print-multi-lib
.;
thumb;@mthumb
hard;@mfloat-abi=hard
thumb/v6-m;@mthumb@march=armv6s-m
thumb/v7-m;@mthumb@march=armv7-m
thumb/v7e-m;@mthumb@march=armv7e-m
thumb/v7-ar;@mthumb@march=armv7
thumb/v8-m.base;@mthumb@march=armv8-m.base
thumb/v8-m.main;@mthumb@march=armv8-m.main
thumb/v7e-m/fpv4-sp/softfp;@mthumb@march=armv7e-m@mfpu=fpv4-sp-d16@mfloat-abi=softfp
thumb/v7e-m/fpv4-sp/hard;@mthumb@march=armv7e-m@mfpu=fpv4-sp-d16@mfloat-abi=hard
thumb/v7e-m/fpv5-sp/softfp;@mthumb@march=armv7e-m@mfpu=fpv5-sp-d16@mfloat-abi=softfp
thumb/v7e-m/fpv5-sp/hard;@mthumb@march=armv7e-m@mfpu=fpv5-sp-d16@mfloat-abi=hard
thumb/v7e-m/fpv5/softfp;@mthumb@march=armv7e-m@mfpu=fpv5-d16@mfloat-abi=softfp
thumb/v7e-m/fpv5/hard;@mthumb@march=armv7e-m@mfpu=fpv5-d16@mfloat-abi=hard
thumb/v7-ar/fpv3/softfp;@mthumb@march=armv7@mfpu=vfpv3-d16@mfloat-abi=softfp
thumb/v7-ar/fpv3/hard;@mthumb@march=armv7@mfpu=vfpv3-d16@mfloat-abi=hard
thumb/v8-m.main/fpv5-sp/softfp;@mthumb@march=armv8-m.main@mfpu=fpv5-sp-d16@mfloat-abi=softfp
thumb/v8-m.main/fpv5-sp/hard;@mthumb@march=armv8-m.main@mfpu=fpv5-sp-d16@mfloat-abi=hard
thumb/v8-m.main/fpv5/softfp;@mthumb@march=armv8-m.main@mfpu=fpv5-d16@mfloat-abi=softfp
thumb/v8-m.main/fpv5/hard;@mthumb@march=armv8-m.main@mfpu=fpv5-d16@mfloat-abi=hard
    ~/ti/ccs830/ccsv8/tools/compiler/gcc-arm-none-eabi-7-2017-q4-major/bin/arm-none-eabi-gcc -print-multi-lib
.;
thumb;@mthumb
hard;@mfloat-abi=hard
thumb/v6-m;@mthumb@march=armv6s-m
thumb/v7-m;@mthumb@march=armv7-m
thumb/v7e-m;@mthumb@march=armv7e-m
thumb/v7-ar;@mthumb@march=armv7
thumb/v8-m.base;@mthumb@march=armv8-m.base
thumb/v8-m.main;@mthumb@march=armv8-m.main
thumb/v7e-m/fpv4-sp/softfp;@mthumb@march=armv7e-m@mfpu=fpv4-sp-d16@mfloat-abi=softfp
thumb/v7e-m/fpv4-sp/hard;@mthumb@march=armv7e-m@mfpu=fpv4-sp-d16@mfloat-abi=hard
thumb/v7e-m/fpv5/softfp;@mthumb@march=armv7e-m@mfpu=fpv5-d16@mfloat-abi=softfp
thumb/v7e-m/fpv5/hard;@mthumb@march=armv7e-m@mfpu=fpv5-d16@mfloat-abi=hard
thumb/v7-ar/fpv3/softfp;@mthumb@march=armv7@mfpu=vfpv3-d16@mfloat-abi=softfp
thumb/v7-ar/fpv3/hard;@mthumb@march=armv7@mfpu=vfpv3-d16@mfloat-abi=hard
thumb/v8-m.main/fpv5-sp/softfp;@mthumb@march=armv8-m.main@mfpu=fpv5-sp-d16@mfloat-abi=softfp
thumb/v8-m.main/fpv5-sp/hard;@mthumb@march=armv8-m.main@mfpu=fpv5-sp-d16@mfloat-abi=hard
thumb/v8-m.main/fpv5/softfp;@mthumb@march=armv8-m.main@mfpu=fpv5-d16@mfloat-abi=softfp
thumb/v8-m.main/fpv5/hard;@mthumb@march=armv8-m.main@mfpu=fpv5-d16@mfloat-abi=hard

    So while the folder tree for the libraries has changed between between versions, a project should select the appropriate library based upon the compiler options without having to add a specific compiler library directory to the search path.

    E.g. for a project for a Cortex-A15 which used the options -marm -mfloat-abi=hard then:

    a. When compiled with v4.9.3 the linker map file showed the library in the fpu directory was linked

    b. When compiled with v7.2.1 the linker map file showed the library in the hard directory was linked.

  • 0 in reply to Chester Gillon
    Genius 4135 points
    Hi, Thank you for your answer.
    I am still a bit unsure - for example regarding the fpu directory taken in the v4.9.3 - which fpu directory is it (as i mentioned, there are several folders named fpu under different folder tree branches)?

    Thanks
    Guy
  • 0 in reply to Guy Mardiks
    Guru 92251 points

    Guy Mardiks said:
    for example regarding the fpu directory taken in the v4.9.3 - which fpu directory is it (as i mentioned, there are several folders named fpu under different folder tree branches)?

    It is the options passed to the linker which select which directory the run-time libraries are linked from, where the output of -print-multi-lib show which options are used used to select the libraries.

    With -marm -mfloat-abi=hard -mfpu=neon-vfpv4 used to target a Cortex-A15 for ARM mode then:

    v4.9.3 links the libraries in gcc-arm-none-eabi-4_9-2015q3/arm-none-eabi/lib/fpu

    v7.2.1 links the libraries in gcc-arm-none-eabi-7-2017-q4-major-win32/arm-none-eabi/lib/hard

    While there are several directories in the v4.9.3 installation named fpu, the arm-none-eabi/lib/fpu is used for ARM mode while the others are used when THUMB mode is selected when linking.

    Looking at the multilib march and mfpu options for the fpu libraries compiled for THUMB, those libraries are either for Cortex-M or for a previous generation FPU than for the VFPv4-D32 in the Cortex-A15. Therefore, recommend leaving -marm as the option passed to the linker to select the ARM mode libraries with -mfloat-abi=hard hardware floating point support (inter-working means the program can contain a mix of ARM and THUMB mode functions).

    While looking into this, found Demystifying ARM Floating Point Compiler Options which contains a useful overview of the -mfpu and -mfloat-abi options.

  • 0 in reply to Chester Gillon
    Genius 4135 points
    Thanks a lot for your answer.

    Regards
    Guy