[issue23270] Use the new __builtin_mul_overflow() of Clang and GCC 5 to check for integer overflow

[STINNER Victor]

STINNER Victor added the comment:

Implementation for any compiler using the new builtin if available:
http://thread.gmane.org/gmane.linux.kernel/204

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[issue23270] Use the new __builtin_mul_overflow() of Clang and GCC 5 to check for integer overflow

[STINNER Victor]

STINNER Victor added the comment:

Implementation for any compiler using the new builtin if available:
http://thread.gmane.org/gmane.linux.kernel/204

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[issue23270] Use the new __builtin_mul_overflow() of Clang and GCC 5 to check for integer overflow

[STINNER Victor]

STINNER Victor added the comment:

I'm no more interested to work on this issue, so I just close it. It was more a 
reminder for myself than a real issue.

--
resolution:  - fixed
status: open - closed

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[issue23270] Use the new __builtin_mul_overflow() of Clang and GCC 5 to check for integer overflow

[STINNER Victor]

New submission from STINNER Victor:

In CPython, almost all memory allocations are protected against integer 
overflow with code looking like that:

if (length  ((PY_SSIZE_T_MAX - struct_size) / char_size - 1)) {
PyErr_NoMemory();
return NULL;
}
new_size = (struct_size + (length + 1) * char_size);

For performances, GCC 5 introduces __builtin_mul_overflow() which is an integer 
multiplication with overflow check. On x86/x86_64, it is implemented in 
hardware (assembler instruction JO, jump if overflow, if I remember correctly).

The function already exists in Clang: ... which existed in Clang/LLVM for a 
while says http://lwn.net/Articles/623368/ According to this mail sent to the 
Linux kernel mailing list, the Linux kernel has functions like 
check_mul_overflow(X, Y, C).

For other compilers, it should be easy to reimplement it, but I don't know what 
is the most efficient implementation (Py_LOCAL_INLINE function in an header?)

GCC 5 changelog:
https://gcc.gnu.org/gcc-5/changes.html

Note: GCC 5 is not released yet.

--
messages: 234310
nosy: haypo
priority: normal
severity: normal
status: open
title: Use the new __builtin_mul_overflow() of Clang and GCC 5 to check for 
integer overflow
versions: Python 3.5

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[issue23270] Use the new __builtin_mul_overflow() of Clang and GCC 5 to check for integer overflow

[STINNER Victor]

Changes by STINNER Victor victor.stin...@gmail.com:


--
components: +Interpreter Core
nosy: +serhiy.storchaka
type:  - performance

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