ustruct Guru Meditation Error crash and blocks the device

[syndycat]

LopY 1.7.8.b1

This type of crash blocks the device.

Simple to reproduce. Type in console:

a= 0xaabbccdd
a.to_bytes(4)
b'\xdd\xcc\xbb\xaa'

import ustruct
ustruct.pack('4b',a)

Guru Meditation Error of type LoadProhibited occurred on core 0. Exception was unhandled.
Register dump:
PC : 0x400ee210 PS : 0x00060030 A0 : 0x800ee403 A1 : 0x3ffc6830
A2 : 0x3ffc6af0 A3 : 0x3ffc6841 A4 : 0x00000001 A5 : 0x3ffe83f2
A6 : 0x000000fb A7 : 0xffffffff A8 : 0x00000000 A9 : 0x0000ccdd
A10 : 0x00000002 A11 : 0x3ffe83f0 A12 : 0x0000ccdd A13 : 0x3ffe83ef
A14 : 0x00000010 A15 : 0x3ffe83f1 SAR : 0x0000001e EXCCAUSE: 0x0000001c
EXCVADDR: 0x00000004 LBEG : 0x4000c28c LEND : 0x4000c296 LCOUNT : 0x00000000

Backtrace: 0x400ee210:0x3ffc6830 0x400ee400:0x3ffc6850 0x400f5ef0:0x3ffc6870 0x400f77ae:0x3ffc68b0 0x400f7801:0x3ffc68f0 0x400f078b:0x3ffc6920 0x400ecc5d:0x3ffc6950 0x400eccc5:0x3ffc6970 0x400f883d:0x3ffc6990 0x400f0710:0x3ffc6a30 0x400ecc5d:0x3ffc6ab0 0x400ecc8a:0x3ffc6ad0 0x400d9953:0x3ffc6af0 0x400d9bf4:0x3ffc6b90 0x400d8c28:0x3ffc6bd0

Guru Meditation Error of type LoadProhibited occurred on core 0. Exception was unhandled.
Register dump:
PC : 0x4008a199 PS : 0x00060033 A0 : 0x80088fd6 A1 : 0x3ffc6470
A2 : 0x3ffc64c0 A3 : 0x3ffc6490 A4 : 0x00000000 A5 : 0x3ffc483c
A6 : 0x00000000 A7 : 0x3ffc4858 A8 : 0x00000012 A9 : 0x3ffc6440
A10 : 0x3ffc6508 A11 : 0x3ffc6490 A12 : 0x3ffb798c A13 : 0x3ffc6850
A14 : 0x3ffc6af0 A15 : 0x00000000 SAR : 0x00000020 EXCCAUSE: 0x0000001c
EXCVADDR: 0x00000000 LBEG : 0x4000c2e0 LEND : 0x4000c2f6 LCOUNT : 0x00000000

Backtrace: 0x4008a199:0x3ffc6470 0x40088fd3:0x3ffc6490 0x4008b2f5:0x3ffc64c0 0x4008b66a:0x3ffc6690 0x4008af75:0x3ffc66d0 0x4008b0f0:0x3ffc6750 0x4008168a:0x3ffc6770 0x400ee20d:0x3ffc6830 0x400ee20d:0x3ffc6850 0x400f5ef0:0x3ffc6870 0x400f77ae:0x3ffc68b0 0x400f7801:0x3ffc68f0 0x400f078b:0x3ffc6920 0x400ecc5d:0x3ffc6950 0x400eccc5:0x3ffc6970 0x400f883d:0x3ffc6990 0x400f0710:0x3ffc6a30 0x400ecc5d:0x3ffc6ab0 0x400ecc8a:0x3ffc6ad0 0x400d9953:0x3ffc6af0 0x400d9bf4:0x3ffc6b90 0x400d8c28:0x3ffc6bd0

[robert-hh]

There were a series of commits in the main branch of micropython.org in that area last night.
https://github.com/micropython/micropython/commits/master
Especially commits:
micropython/micropython@2daacc5
micropython/micropython@79d5acb
micropython/micropython@793d826

[robert-hh]

Using the file py/modstruct.c from the micropython.org branch fixes that problem of a crash.
The result is:
ustruct.pack('4b',a)
b'\xdd\x00\x00\x00'
However
ustruct.pack('I',a)
b'\xdd\xcc\xbb\xaa'
Note that Cpython refuses to perform struct.pack('4b',a), claiming to expect four values instead of one.

[danicampora]

This is being fixed with @robert-hh's pulls request, but please note that doing:

a = 0xaabbccdd
a.to_bytes(4)

it wrong because the to_bytes() method requires the byte order to be passed as well (https://docs.python.org/3.2/library/stdtypes.html#int.to_bytes), so allowing it to work without that parameter was wrong. From the next release onwards you will have to do:

a.to_bytes(4, 'little')

Cheers,
Daniel