Build profiles

Arm Mbed OS 5 defines three collections of toolchain flags used during the build. These are build profiles. The three build profiles are develop, debug and release. The Mbed Online Compiler uses the develop build profile. When building from Arm Mbed CLI, you may select the build profile by passing your desired build profile, by name or path, to the --profile argument.

Develop

• Small and fast code.
• Full error information. For example, asserts have file name and line number.
• Hard to follow code flow when using a debugger.
• Chip goes to sleep when idle:
  • Debugger is likely to drop connection.
  • Breaks the local file system on the Arm Mbed interface on some boards.

Debug

• Largest and slowest performance.
• Full error information. For example, asserts have file name and line number.
• Easy to step through code with a debugger.
• Disabled sleep mode.

Note: The debug profile uses optimization flags that may cause unwanted behavior during debugging (such as out-of-order jumps and optimized-out variables). If this occurs, you can set the compiler to the lowest possible optimization setting (for example, change -Og to -O0 for GCC). See your toolchain's documentation for more information.

Release

• Smallest code size and still fast.
• Minimal error information.
• Chip goes to sleep when going idle:
  • Debugger is likely to drop connection.
  • Breaks the local file system on the Mbed interface on some boards.

User-defined build profile

As mentioned above, the build profile defines the set of flags that is passed to the underlying compiler suite. You can also create a custom or user-defined build profile using a JSON file according to the build profile format mentioned in JSON build profile format.

These flags stored in the JSON file are merged with other JSON files of the same structure when multiple --profile arguments are passed on the command line.

JSON build profile format

The build profiles are JSON files with the root object containing key-value pairs for each supported toolchain, such as GCC_ARM. Each key is a toolchain name and every value contains a mapping from a flag type to a list of flags that should be passed to the corresponding part of the compiler suite.

The required flag types are:

Example

An example of a build profile:

{
    "GCC_ARM": {
        "common": ["-c", "-Wall", "-Wextra",
                   "-Wno-unused-parameter", "-Wno-missing-field-initializers",
                   "-fmessage-length=0", "-fno-exceptions", "-fno-builtin",
                   "-ffunction-sections", "-fdata-sections", "-funsigned-char",
                   "-MMD", "-fno-delete-null-pointer-checks",
                   "-fomit-frame-pointer", "-Os"],
        "asm": ["-x", "assembler-with-cpp"],
        "c": ["-std=gnu99"],
        "cxx": ["-std=gnu++98", "-fno-rtti", "-Wvla"],
        "ld": ["-Wl,--gc-sections", "-Wl,--wrap,main", "-Wl,--wrap,_malloc_r",
               "-Wl,--wrap,_free_r", "-Wl,--wrap,_realloc_r",
               "-Wl,--wrap,_calloc_r", "-Wl,--wrap,exit", "-Wl,--wrap,atexit"]
    },
    "ARM": {
        "common": ["-c", "--gnu", "-Otime", "--split_sections",
                   "--apcs=interwork", "--brief_diagnostics", "--restrict",
                   "--multibyte_chars", "-O3"],
        "asm": [],
        "c": ["--md", "--no_depend_system_headers", "--c99", "-D__ASSERT_MSG"],
        "cxx": ["--cpp", "--no_rtti", "--no_vla"],
        "ld": []
    },
    "IAR": {
        "common": [
            "--no_wrap_diagnostics", "non-native end of line sequence", "-e",
            "--diag_suppress=Pa050,Pa084,Pa093,Pa082", "-Oh"],
        "asm": [],
        "c": ["--vla"],
        "cxx": ["--guard_calls", "--no_static_destruction"],
        "ld": ["--skip_dynamic_initialization", "--threaded_lib"]
    }
}

In the above example, you can tell that:

• GCC_ARM, ARM and IAR compiler suites are supported.
• The ARM C and C++ compilers use optimization level -O3.
• The IAR linker skips dynamic initialization.

And so on.