As TF-M needs runtime APIs so we are creating the Secure Partition runtime library, code is ready but we have not forwarded all necessary runtime APIs to the version TF-M implemented, this was caused by the toolchain optimization for built-in APIs, such as:

• Forward printf(%s) to puts if there is only one string parameter.
• ARMCLANG would forward memxxx API into an optimized variant.

With the '-fno-builtin' flags set in the toolchain, this optimization would be disabled so that user just implement the same name built-in to replace the toolchain version.

Please help to check these point before applying '-fno-builtin' and provide your feedback:

• Could toolchains out of ARMCLANG and GNUARM have a similar flag?
• Would it affect your project setting and how does it affect?