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bitfield layout wrong in ctypes #84039
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thesamprice commented
on Mar 5, 2020 thesampricemannequinMannequinAuthorif 8 1 byte fields are included in a ctype field, it allows an extra byte to be included in the packing when there is no room left for the next field.
If I put the bitfields in a child structure then I get expected results.
In [35]: run ctypeSizeTest.py
Size is 4 Expected 3
0 0x10000 a0
0 0x10001 a1
0 0x10002 a2
0 0x10003 a3
0 0x10004 a4
0 0x10005 a5
0 0x10006 a6
0 0x10007 a7
0 0x40008 b0 <- Expected to be at offset 1, not 0.
2 0xc0000 b1 <- Expected to be at offset 1, not 2
Size is 3 Expected 3
0 0x1 a
1 0x40000 b0
1 0xc0004 b1thesamprice commented
on Mar 5, 2020 thesampricemannequinMannequinAuthorDoes not happen on windows.
Error is in cfield.c
#ifndef MS_WIN32 } else if (bitsize /* this is a bitfield request */ && *pfield_size /* we have a bitfield open */ && dict->size * 8 >= *pfield_size && (*pbitofs + bitsize) <= dict->size * 8) { /* expand bit field */ fieldtype = EXPAND_BITFIELD; #endifSpecifically dict->size * 8 >= *pfield_size
if *bitofs == *pfield_size then the current field is filled, and expanding the bitfield should not be done.Consider adding this *pfield_size != *bitofs #ifndef MS_WIN32 } else if (bitsize /* this is a bitfield request */ && *pfield_size /* we have a bitfield open */ && *pfield_size != *pbitofs /* Current field has been filled, start new one */ && dict->size * 8 >= *pfield_size && (*pbitofs + bitsize) <= dict->size * 8) { /* expand bit field */ fieldtype = EXPAND_BITFIELD; #endif
Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.
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