Work around ARM and IAR optimization issue

[Patater]

Add a custom profile to work around an issue with the ARM and IAR
compilers, where the example appears to hang without any error. Building
the example with -O1, rather than the default of -Os, works as a
workaround.

To use the custom profile with mbed-cli, use the --profile option.

mbed compile -m CY8CKIT_062_WIFI_BT -t ARMC6 --profile mbed_profile.json

Arm internal reference: SDCTRESPONSE-3550

[gilles-peskine-arm]

The command line in the commit message is wrong given the commit contents: since mbed_profile.json only contains settings to change from the default profile, the default profile needs to be listed explicitly.

mbed compile -m CY8CKIT_062_WIFI_BT -t ARMC6 --profile mbed-os/tools/profiles/develop.json --profile mbed_profile.json

With the command line above, I have verified that the build produces significantly larger object files compared to the default profile, which is evidence that the optimization level changed from -Os to -O1. However the content of the file is fragile, see my comments.

[gilles-peskine-arm]

Please add "GCC_ARM": {} so that we can use the same command line regardless of the target.

(Arguably the fact that mbed compile -t FOO --profile P1 --profile P2 requires FOO to have an entry in both P1 and P2 is a bug in mbed-cli, but we have to work with mbed-cli as it is.)

[Patater]

I was expecting the user not to pass the profile option if they didn't need the workaround. I've added all toolchains, since there is at least one user who wanted to use the profile options on non-affected toolchains.

[gilles-peskine-arm]

Running the build with mbed compile -vv … shows that if this is used to override the default profile, the compiler command line combines options from the two profile files. Repeating options here is not only superfluous, it's misleading, since for example if we wanted to avoid a -DFOO in the default profile we'd need to have -UFOO here. Therefore this should just be "common": ["-Os"]. The same goes for IAR.

Alternatively, if this profile is meant to be used on its own, it needs to have the settings for the other tools ("c", "cxx", "ld"). Otherwise the build fails.

[Patater]

I went back and forth on standalone or not. You are correct that the IAR build failed without the other options. The ARMC6 build, as listed in the commit message, worked OK.

Primarily for maintainability sake, I've switch to override style and now require both profile options to be specified. This also allows use of the release profile or debug profile with the workaround, whereas with the standalone profile you were forced into a "develop"-like profile.

[dgreen-arm]

When using this profile, I get errors due to variable length arrays not being enabled. I'd suggest adding the rest of the mbed-os profile information:

        "asm": [],
        "c": ["--vla", "--diag_suppress=Pe546"],
        "cxx": ["--guard_calls", "--no_static_destruction"],
        "ld": ["--skip_dynamic_initialization", "--threaded_lib"]

[Patater]

Please try again with latest patch set.

[Patater]

New patch set lists all toolchains explicitly, for users who want to always pass --profile even to non-affected toolchains. The new patch set also is no longer standalone and requires passing of another profile first to be overridden.

Tested working with CY8CKIT_062_WIFI_BT: develop profile and ARMC6, develop profile and GCC_ARM, release profile and ARMC6, debug profile and ARMC6.

[dgreen-arm]

This causes an error with IAR: [ERROR] Command line error: Option -O can only occur once

[Patater]

Bah, so we need a standalone profile. I am not a fan of maintaining that. I'll see if we can take a better approach.

[Patater]

Took approach of reducing stack usage of the example instead.

#49