ARM Compiler 6.13 testing revealed linker errors pointing out
conflicting use of `__user_setup_stackheap` and
`__user_initial_stackheap` in some targets. Remove the unwanted
`__user_initial_stackheap` from the targets - the setup is
centralised in the common platform code.
Looking into this, a number of other issues were highlighted
* Almost all targets had `__initial_sp` hardcoded in assembler,
rather than getting it from the scatter file. This was behind
issue #11313. Fix this generally.
* A few targets' `__initial_sp` values did not match the scatter
file layout, in some cases meaning they were overlapping heap
space. They now all use the area reserved in the scatter file.
If any problems are seen, then there is an error in the
scatter file.
* A number of targets were reserving unneeded space for heap and
stack in their startup assembler, on top of the space reserved in
the scatter file, so wasting a few K. A couple were using that
space for the stack, rather than the space in the scatter file.
To clarify expected behaviour:
* Each scatter file contains empty regions `ARM_LIB_HEAP` and
`ARM_LIB_STACK` to reserve space. `ARM_LIB_STACK` is sized
by the macro `MBED_BOOT_STACK_SIZE`, which is set by the tools.
`ARM_LIB_HEAP` is generally the space left over after static
RAM and stack.
* The address of the end of `ARM_LIB_STACK` is written into the
vector table and on reset the CPU sets MSP to that address.
* The common platform code in Mbed OS provides `__user_setup_stackheap`
for the ARM library. The ARM library calls this during startup, and
it calls `__mbed_user_setup_stackheap`.
* The default weak definition of `__mbed_user_setup_stackheap` does not
modify SP, so we remain on the boot stack, and the heap is set to
the region described by `ARM_LIB_HEAP`. If `ARM_LIB_HEAP` doesn't
exist, then the heap is the space from the end of the used data in
`RW_IRAM1` to the start of `ARM_LIB_STACK`.
* Targets can override `__mbed_user_setup_stackheap` if they want.
Currently only Renesas (ARMv7-A class) devices do.
* If microlib is in use, then it doesn't call `__user_setup_stackheap`.
Instead it just finds and uses `ARM_LIB_STACK` and `ARM_LIB_HEAP`
itself.
--legacyalign, --no_legacyalign are deprecated from ARMC6 compiler, in order to
remove deprecated flags all linker files should strictly align to 8-byte boundary
Adam Mitchell
Kevin Bracey
Teijo Kinnunen
jeromecoutant
Deepika
Przemyslaw Stekiel
bcostm
Wilfried Chauveau