printf() linker error – "undefined reference to `_sbrk'"

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  • January 10, 2017 at 22:57 #10023
    bmcdonnell_psi
    Participant

    I have an STM32F072RB project using the toolchain ARM in C:\SysGCC\arm-eabi.

    When I try to build my project and it includes an integer to string conversion using any function in the printf() family (sprintf(), vsnprintf(), etc.), I get the following linker error.

    Severity Code Description Project File Line Suppression State
    Error undefined reference to `_sbrk’ MyProject q:\gnu\newlib-nano\newlib-nano-2016q3\newlib\libc\reent\sbrkr.c 58
    Error ld returned 1 exit status MyProject C:\[path to MyProject]\collect2.exe 1

    Why is this happening, and how can I fix it?

     

    I have the latest VisualGDB packages, as shown below.

    • This topic was modified 7 years, 10 months ago by bmcdonnell_psi. Reason: add version details
    January 10, 2017 at 23:20 #10025
    bmcdonnell_psi
    Participant

    Actually, it’s not just for number conversions. Maybe for every time there’s a format string followed by one or more var args? I’m not totally sure the circumstances.

    January 11, 2017 at 06:00 #10031
    support
    Keymaster

    Hi,

    This error happens because the newlib-nano does not include the default implementations for system calls like _sbrk().

    To fix this, please simply enable the ‘provide default implementations for system calls’ checkbox on the first page of VisualGDB Project Properties.

    April 13, 2017 at 16:37 #10987
    chris250
    Participant

    Hi,

    I am also getting this error. I am currently using a 5.2r9 trial version and I am building for the STM32F746.

    I have read the instruction above but I can not find the ‘provide default implementations for system calls’ checkbox anywhere. I have looked in various places, including: right click on Project, VisualGDB Project Properties.

    I would be very grateful for some help.

    Thanks

    April 13, 2017 at 16:54 #10988
    chris250
    Participant

    Sorry to repost but I should add some more information for you…

    I am using the latest ARM toolchain: 6-2017-q1-update. This is installed to c:\SysGCC\6_2017-q1-update.

    The VisualGDB package manager does not display the GCC or GDB versions for this, but it does compile the project. It fails at the linking stage (sbrk).

    Thanks

    April 13, 2017 at 17:25 #10989
    chris250
    Participant

    3rd post in a row 🙂

    Typical – I had been looking at this for a few hours and as soon as I post a question … I find the answer myself!!!

    I was using the latest toolchain that I had downloaded from ARM. I am now using the Prebuilt GNU toolchain for arm-eabi downloaded from sysprogs and it works.

    Thanks

    April 14, 2017 at 03:12 #10991
    support
    Keymaster

    Hi,

    For a 3rd-party toolchain you would need to manually specify “–specs=nosys.specs” via LDFLAGS to include the necessary libraries. The toolchains shipped by us have this flag conveniently mapped to a checkbox in the settings, but 3rd-party toolchains would require specifying it manually.

    April 18, 2017 at 12:19 #11014
    chris250
    Participant

    Hi,

    Thanks for your answer – I am using the toolchains shipped by yourselves now as they work straight away with no issues!

    Thanks

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