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gh-96735: Fix undefined behaviour in struct unpacking functions #96739

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Merged
mdickinson merged 10 commits into from
Sep 25, 2022
Merged

gh-96735: Fix undefined behaviour in struct unpacking functions #96739

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22fdce6
Fix undefined behaviour in bu_ulonglong
mdickinson Sep 10, 2022
e12943b
Add regression test
mdickinson Sep 10, 2022
8efefd8
Also apply the fix to lu_longlong
mdickinson Sep 10, 2022
cba4b8b
Merge branch 'main' into fix-struct-unpack-undefined-behaviour
mdickinson Sep 10, 2022
0d49e73
Fix similar undefined behaviour issues in bu_int and lu_int
mdickinson Sep 10, 2022
bfd714f
Merge remote-tracking branch 'mdickinson/fix-struct-unpack-undefined-…
mdickinson Sep 10, 2022
5aeef09
Remove redundant test
mdickinson Sep 10, 2022
204e924
Fix accumulator type
mdickinson Sep 10, 2022
994703e
Branch-free sign-extension
mdickinson Sep 13, 2022
1294440
Fix unconventional spacing
mdickinson Sep 13, 2022
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Branch-free sign-extension
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@mdickinson
mdickinson committed Sep 13, 2022
commit 994703e10e0af676559a7028ba77afee4e2bcb23
28 changes: 16 additions & 12 deletions Modules/_struct.c
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Original file line number Diff line number Diff line change
Expand Up @@ -817,8 +817,9 @@ bu_short(_structmodulestate *state, const char *p, const formatdef *f)
do {
x = (x<<8) | *bytes++;
} while (--i > 0);
/* Extend sign. */
return PyLong_FromLong(x & 0x8000U ? (long)x - 0x10000 : (long)x);
/* Extend sign, avoiding implementation-defined or undefined behaviour. */
x = (x ^ 0x8000U) - 0x8000U;
return PyLong_FromLong(x & 0x8000U ? -1 - (long)(~x): (long)x);
}

static PyObject *
Expand All @@ -834,8 +835,8 @@ bu_int(_structmodulestate *state, const char *p, const formatdef *f)
x = (x<<8) | *bytes++;
} while (--i > 0);
/* Extend sign, avoiding implementation-defined or undefined behaviour. */
return PyLong_FromLong(x & 0x80000000U ?
-1 - (long)(0xFFFFFFFFU - x) : (long)x);
x = (x ^ 0x80000000U) - 0x80000000U;
return PyLong_FromLong(x & 0x80000000U ? -1 - (long)(~x): (long)x);
}

static PyObject *
Expand Down Expand Up @@ -863,8 +864,9 @@ bu_longlong(_structmodulestate *state, const char *p, const formatdef *f)
x = (x<<8) | *bytes++;
} while (--i > 0);
/* Extend sign, avoiding implementation-defined or undefined behaviour. */
return PyLong_FromLongLong(x & 0x8000000000000000U ?
-1 - (long long)(0xFFFFFFFFFFFFFFFFU - x) : (long long)x);
x = (x ^ 0x8000000000000000U) - 0x8000000000000000U;
return PyLong_FromLongLong(
x & 0x8000000000000000U ? -1 - (long long)(~x): (long long)x);
}

static PyObject *
Expand Down Expand Up @@ -1058,8 +1060,9 @@ lu_short(_structmodulestate *state, const char *p, const formatdef *f)
do {
x = (x<<8) | bytes[--i];
} while (i > 0);
/* Extend sign. */
return PyLong_FromLong(x & 0x8000U ? (long)x - 0x10000 : (long)x);
/* Extend sign, avoiding implementation-defined or undefined behaviour. */
x = (x ^ 0x8000U) - 0x8000U;
return PyLong_FromLong(x & 0x8000U ? -1 - (long)(~x): (long)x);
}

static PyObject *
Expand All @@ -1075,8 +1078,8 @@ lu_int(_structmodulestate *state, const char *p, const formatdef *f)
x = (x<<8) | bytes[--i];
} while (i > 0);
/* Extend sign, avoiding implementation-defined or undefined behaviour. */
return PyLong_FromLong(x & 0x80000000U ?
-1 - (long)(0xFFFFFFFFU - x) : (long)x);
x = (x ^ 0x80000000U) - 0x80000000U;
return PyLong_FromLong(x & 0x80000000U ? -1 - (long)(~x): (long)x);
}

static PyObject *
Expand Down Expand Up @@ -1104,8 +1107,9 @@ lu_longlong(_structmodulestate *state, const char *p, const formatdef *f)
x = (x<<8) | bytes[--i];
} while (i > 0);
/* Extend sign, avoiding implementation-defined or undefined behaviour. */
return PyLong_FromLongLong(x & 0x8000000000000000U ?
-1 - (long long)(0xFFFFFFFFFFFFFFFFU - x) : (long long)x);
x = (x ^ 0x8000000000000000U) - 0x8000000000000000U;
return PyLong_FromLongLong(
x & 0x8000000000000000U ? -1 - (long long)(~x): (long long)x);
}

static PyObject *
Expand Down