make mpy-cross "-Werror=dangling-pointer=" error

[sunpub]

Problem

use MSYS2 to make "mpy-cross" got some error:
$ make
Use make V=1 or set BUILD_VERBOSE in your environment to increase build verbosity.
mkdir -p build/genhdr
GEN build/genhdr/mpversion.h
GEN build/genhdr/qstr.i.last
GEN build/genhdr/qstr.split
GEN build/genhdr/qstrdefs.collected.h
QSTR updated
GEN build/genhdr/qstrdefs.generated.h
GEN build/genhdr/moduledefs.split
GEN build/genhdr/moduledefs.collected
Module registrations updated
GEN build/genhdr/moduledefs.h
GEN build/genhdr/root_pointers.split
GEN build/genhdr/root_pointers.collected
Root pointer registrations updated
GEN build/genhdr/root_pointers.h
mkdir -p build/ports/windows/
mkdir -p build/py/
mkdir -p build/shared/runtime/
CC ../py/mpstate.c
CC ../py/nlr.c
CC ../py/nlrx86.c
CC ../py/nlrx64.c
CC ../py/nlrthumb.c
CC ../py/nlraarch64.c
CC ../py/nlrmips.c
CC ../py/nlrpowerpc.c
CC ../py/nlrxtensa.c
CC ../py/nlrsetjmp.c
CC ../py/malloc.c
CC ../py/gc.c
CC ../py/pystack.c
CC ../py/qstr.c
CC ../py/vstr.c
CC ../py/mpprint.c
CC ../py/unicode.c
CC ../py/mpz.c
CC ../py/reader.c
CC ../py/lexer.c
CC ../py/parse.c
CC ../py/scope.c
CC ../py/compile.c
CC ../py/emitcommon.c
CC ../py/emitbc.c
CC ../py/asmbase.c
CC ../py/asmx64.c
CC ../py/emitnx64.c
CC ../py/asmx86.c
CC ../py/emitnx86.c
CC ../py/asmthumb.c
CC ../py/emitnthumb.c
CC ../py/emitinlinethumb.c
CC ../py/asmarm.c
CC ../py/emitnarm.c
CC ../py/asmxtensa.c
CC ../py/emitnxtensa.c
CC ../py/emitinlinextensa.c
CC ../py/emitnxtensawin.c
CC ../py/formatfloat.c
CC ../py/parsenumbase.c
CC ../py/parsenum.c
CC ../py/emitglue.c
CC ../py/persistentcode.c
CC ../py/runtime.c
CC ../py/runtime_utils.c
CC ../py/scheduler.c
CC ../py/nativeglue.c
CC ../py/pairheap.c
CC ../py/ringbuf.c
CC ../py/stackctrl.c
../py/stackctrl.c: In function 'mp_stack_ctrl_init':
../py/stackctrl.c:32:32: error: storing the address of local variable 'stack_dummy' in 'mp_state_ctx.thread.stack_top' [-Werror=dangling-pointer=]
32 | MP_STATE_THREAD(stack_top) = (char *)&stack_dummy;
../py/stackctrl.c:31:18: note: 'stack_dummy' declared here
31 | volatile int stack_dummy;
| ^~~~~~~~~~~
In file included from ../py/runtime.h:29,
from ../py/stackctrl.c:27:
../py/mpstate.h:296:23: note: 'mp_state_ctx' declared here
296 | extern mp_state_ctx_t mp_state_ctx;
| ^~~~~~~~~~~~
cc1.exe: all warnings being treated as errors
See https://github.com/micropython/micropython/wiki/Build-Troubleshooting
make: *** [../py/mkrules.mk:83: build/py/stackctrl.o] Error 1

Reason

in file ../py/stackctrl.c has this code:

void mp_stack_ctrl_init(void) {
volatile int stack_dummy;
MP_STATE_THREAD(stack_top) = (char *)&stack_dummy;
}
it can occur -Werror=dangling-pointer= error

Resolve

change stack_dummy declear to static variable:

void mp_stack_ctrl_init(void) {
static volatile int stack_dummy=0;
MP_STATE_THREAD(stack_top) = (char *)&stack_dummy;
}
but, I'm not sure it correct.

[dlech]

but, I'm not sure it correct.

It is very much not correct. The MicroPython runtime (bytecode interpreter) needs to know about the C stack. If you make the variable static, it is no longer on the stack.

Instead, I would use #pragma to disable this check for this specific function. This is a dangling pointer, but it is intentional in this case.

[sunpub]

thank you very much.
could you tell me the details about how to use #pragma to disable this check

[sunpub]

i found it.
add
#pragma GCC diagnostic ignored "-Wdangling-pointer=1"
to ../py/stackctrl.c can disable check
thanks a lot

[Inouali]

can you explained to me please