Tony Reix <tony.r...@atos.net> added the comment:
After more investigations, we (Damien and I) think that there are several issues in Python 3.8.5 : 1) Documentation. a) AFAIK, the only place in the Python ctypes documentation where it talks about how arrays in a structure are managed appears at: https://docs.python.org/3/library/ctypes.html#arrays b) the size of the structure in the example given here is much greater than in our case. c) The documentation does NOT talk that a structure <= 16 bytes and a structure greater than 16 bytes are managed differently. That's a bug in the documentation vs the code. 2) Tests Looking at tests, there are NO test about our case. 3) There is a bug in Python About the issue here, we see with gdb that Python provides libffi with a description saying that our case is passed as pointers. However, Python does NOT provides libffi with pointers for the array c_n, but with values. 4) libffi obeys Python directives given in description, thinking that it deals with 2 pointers, and thus it pushes only 2 values in registers R3 and R4. ===================================================== Bug in Python: ----------------------------------------------------- 1) gdb (gdb) b ffi_call Breakpoint 1 at 0x9000000016fab80: file ../src/powerpc/ffi_darwin.c, line 919. (gdb) run Starting program: /home2/freeware/bin/python3 /tmp/Pb_damien2.py Thread 2 hit Breakpoint 1, ffi_call (cif=0xfffffffffffd108, fn=@0x9001000a0082640: 0x9000000001b0d60 <memchr>, rvalue=0xfffffffffffd1d0, avalue=0xfffffffffffd1c0) (gdb) p *(ffi_cif *)$r3 $9 = {abi = FFI_AIX, nargs = 2, arg_types = 0xfffffffffffd1b0, rtype = 0xa00000000435cb8, bytes = 144, flags = 8} (gdb) x/2xg 0xfffffffffffd1b0 0xfffffffffffd1b0: 0x0a0000000043ca48 0x08001000a0002a10 (gdb) p *(ffi_type *)0x0a0000000043ca48 $11 = {size = 16, alignment = 8, type = 13, elements = 0xa0000000012eed0} <= 13==FFI_TYPE_STRUCT size == 16 on AIX!!! == 24 on Linux (gdb) p *(ffi_type *)0x08001000a0002a10 $12 = {size = 8, alignment = 8, type = 14, elements = 0x0} <= FFI_TYPE_POINTER (gdb) x/3xg *(long *)$r6 0xa00000000436050: 0x0a00000000152200 0x0000000000000064 0xa00000000436060: 0x0000000000000007 <= 7 is present in avalue[2] (gdb) x/s 0x0a00000000152200 0xa00000000152200: "abcdef" ----------------------------------------------------- 2) prints in libffi: AIX : aix_adjust_aggregate_sizes() TONY: libffi: src/powerpc/ffi_darwin.c : aix_adjust_aggregate_sizes() s->size: 8 s->type:14 : FFI_TYPE_POINTER TONY: libffi: src/powerpc/ffi_darwin.c : aix_adjust_aggregate_sizes() s->size:24 s->type:13 : FFI_TYPE_STRUCT TONY: libffi: src/powerpc/ffi_darwin.c : aix_adjust_aggregate_sizes() FFI_TYPE_STRUCT Before s->size:24 TONY: libffi: src/powerpc/ffi_darwin.c : aix_adjust_aggregate_sizes() s->size: 8 s->type:14 : FFI_TYPE_POINTER TONY: libffi: src/powerpc/ffi_darwin.c : aix_adjust_aggregate_sizes() p->size: 8 s->size: 8 TONY: libffi: src/powerpc/ffi_darwin.c : aix_adjust_aggregate_sizes() s->size: 8 s->type:14 : FFI_TYPE_POINTER TONY: libffi: src/powerpc/ffi_darwin.c : aix_adjust_aggregate_sizes() p->size: 8 s->size:16 TONY: libffi: src/powerpc/ffi_darwin.c : aix_adjust_aggregate_sizes() After ALIGN s->size:16 TONY: libffi: src/powerpc/ffi_darwin.c : aix_adjust_aggregate_sizes() s->size: 8 s->type:14 : FFI_TYPE_POINTER TONY: libffi: src/powerpc/ffi_darwin.c: ffi_call: FFI_AIX TONY: libffi: cif->abi: 1 -(long)cif->bytes : -144 cif->flags : 8 ecif.rvalue : fffffffffffd200 fn: 9001000a0227760 FFI_FN(ffi_prep_args) : 9001000a050a108 s element : char pointer: a00000000153d40 abcdef c_n element 0: a Long: 100 0X64 = 100 instead of a pointer c_n element 1: a Long: 0 libffi obeys description given by Python and pushes to R4 only what it thinks is a pointer (100 instead), and nothing in R5 ==================================================================== Summary: - Python documentation is uncomplete vs the code - Python code gives libffi a description about pointers but Python code provides libffi with values. ---------- _______________________________________ Python tracker <rep...@bugs.python.org> <https://bugs.python.org/issue38628> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
