Disable global objects destruction

[pan-]

Description

This pull request disable the destruction of global objects when exit is called.
A different method is applied for each compiler:

• IAR: use the compilation flag --no_static_destruction.
• ARMCC: override __aeabi_atexit, __cxa_atexit and __cxa_finalize. The methodology is explained here.
• GCC: For GCC it is a bit more complicated, depending on how it is compiled, it is possible or not to override the itanium abi calls. To ensure that the correct behavior is used, exit has been overridden to directly call _exit instead of calling in reverse order every function registered by atexit. In the meantime, atexit has been overridden to be a stub which does nothing.

Related PRs

This PR is a follow up of #2715 #2741

Gain:

The test have been conducted upon mbed-os-example-blinky compiled with NDEBUG enabled.

• Without the patch:

	GCC	ARMCC	IAR
RAM	11832	10152	7970
ROM	37008	26868	21266

• With this patch Allow the trace output by mbed error to be conditional of NDEBUG. #2715 and Add configuration for IO flushing during exit. #2741 applied:

	GCC	ARMCC	IAR
RAM	9236 bytes	8020 bytes	7350 bytes
ROM	11480 bytes	12686 bytes	12398 bytes

• Difference:

	GCC	ARMCC	IAR
RAM	-2596 bytes (-21.94%)	-2132 bytes (-21%)	-620 bytes (7.8%)
ROM	-25528 bytes (-68.97%)	-14686 bytes (-52.8%)	-8868 bytes (-41.7%)

[pan-]

@c1728p9 @geky @sg- @0xc0170 Could you review this PR ?

I wonder if completely shutting down atexit is reasonable for GCC or should I re-implement it with the basic requirements implied by the C standard (32 entries) ?

If so, what is the use case ? We're never supposed to exit our applications.

[0xc0170]

I wonder if completely shutting down atexit is reasonable for GCC or should I re-implement it with the basic requirements implied by the C standard (32 entries) ?

Can you elaborate? how does this differ from the rest toolchains?

[pan-]

This PR shutdown completely atexit on GCC while on other toolchains it shutdowns __aeabi_atexit .

On ARMCC, the result is identical to shutting down atexit while on IAR it depends if the application is compiled with aeabi compatibility enabled. Also, on IAR, the atexit behavior is already non compliant with the C library, it only stores 10 entries instead of the 32 from the C standard.

[0xc0170]

This PR shutdown completely atexit on GCC while on other toolchains it shutdowns __aeabi_atexit .

Good to know, I would have assumed all of them would do __eabi_atexit.

Also, on IAR, the atexit behavior is already non compliant with the C library, it only stores 10 entries instead of the 32 from the C standard.

Memory savings? 😄 We can ask IAR.

Looks good to me the way it is.

[sg-]

/morph test

[sg-]

@mbed-bot: TEST

HOST_OSES=ALL
BUILD_TOOLCHAINS=ALL
TARGETS=ALL

[mbed-bot]

Result: SUCCESS

Your command has finished executing! Here's what you wrote!

/morph test

Output

mbed Build Number: 906

All builds and test passed!

[mbed-bot]

[Build 952]
SUCCESS: Building succeeded and tests were run! Be sure to check the test results