This tracing was originally needed for three reasons:
1. To trace object/raw-code pointers embedded in native code, eg from
@micropython.native functions.
2. To trace pointers to BSS/rodata from relocated viper code.
3. For libffi tracing.
The tracing in point 1 was made unnecessary long ago in commit
7d4b6cc868 (see also commit
bbccb0f630 which removed scanning of native
code on the esp8266 port).
Since the previous commit, point 2 is no longer needed.
For point 3, this was made unnecessary in the recent commit
9796625457.
Signed-off-by: Damien George <damien@micropython.org>
No functionality change is intended with this commit, it just consolidates
the separate implementations of GC helper code to the lib/utils/ directory
as a general set of helper functions useful for any port. This reduces
duplication of code, and makes it easier for future ports or embedders to
get the GC implementation correct.
Ports should now link against gchelper_native.c and either gchelper_m0.s or
gchelper_m3.s (currently only Cortex-M is supported but other architectures
can follow), or use the fallback gchelper_generic.c which will work on
x86/x64/ARM.
The gc_helper_get_sp function from gchelper_m3.s is not really GC related
and was only used by cc3200, so it has been moved to that port and renamed
to cortex_m3_get_sp.
Note: the uncrustify configuration is explicitly set to 'add' instead of
'force' in order not to alter the comments which use extra spaces after //
as a means of indenting text for clarity.
When building with link time optimization enabled it is possible both
gc_collect() and gc_collect_regs_and_stack() get inlined into gc_alloc()
which can result in the regs variable being pushed on the stack earlier
than some of the registers. Depending on the calling convention, those
registers might however contain pointers to blocks which have just been
allocated in the caller of gc_alloc(). Then those pointers end up higher on
the stack than regs, aren't marked by gc_collect_root() and hence get
sweeped, even though they're still in use.
As reported in #4652 this happened for in 32-bit msvc release builds:
mp_lexer_new() does two consecutive allocations and the latter triggered a
gc_collect() which would sweep the memory of the first allocation again.
This is to keep the top-level directory clean, to make it clear what is
core and what is a port, and to allow the repository to grow with new ports
in a sustainable way.
