[issue27278] py_getrandom() uses an int for syscall() result

[STINNER Victor]

STINNER Victor added the comment:

> Adding a cast would solve this compiler warning:

I changed the code to use the long type. It should fix the warning, even if it 
was no more a real bug: the original bug was already fixed.

I close the issue, it's now solved.

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resolution:  -> fixed
status: open -> closed

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[issue27278] py_getrandom() uses an int for syscall() result

[Roundup Robot]

Roundup Robot added the comment:

New changeset 193f50babfa4 by Victor Stinner in branch '3.5':
py_getrandom(): use long type for the syscall() result
https://hg.python.org/cpython/rev/193f50babfa4

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[issue27278] py_getrandom() uses an int for syscall() result

[Martin Panter]

Martin Panter added the comment:

Yeah I think your change is enough.

Adding a cast would solve this compiler warning:

Python/random.c:168:17: warning: conversion to ‘int’ from ‘long int’ may alter 
its value [-Wconversion]
 n = syscall(SYS_getrandom, dest, n, flags);
 ^

But on the other hand, when I just recompiled Python with -Wconversion, I got 
hundreds of other warnings, so maybe there is a good reason we don’t enable 
that warning.

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[issue27278] py_getrandom() uses an int for syscall() result

[STINNER Victor]

STINNER Victor added the comment:

Martin: What do you think of my change? Is it enough? Or would you prefer an 
explicit cast on syscall() result?

I hesitated to use a wider type since the manual page shows an "int" type, not 
long.

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[issue27278] py_getrandom() uses an int for syscall() result

[Roundup Robot]

Roundup Robot added the comment:

New changeset e028e86a5b73 by Victor Stinner in branch '3.5':
Fix os.urandom() using getrandom() on Linux
https://hg.python.org/cpython/rev/e028e86a5b73

New changeset 0d39bd9028e8 by Victor Stinner in branch 'default':
Merge 3.5 (os.urandom, issue #27278)
https://hg.python.org/cpython/rev/0d39bd9028e8

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nosy: +python-dev

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[issue27278] py_getrandom() uses an int for syscall() result

[Martin Panter]

Martin Panter added the comment:

Make that INT_MAX. Or change n from an int to a Py_ssize_t. Both Linux and 
Solaris versions or getrandom() are documented as accepting size_t buflen.

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[issue27278] py_getrandom() uses an int for syscall() result

[Martin Panter]

Martin Panter added the comment:

According to , 
getrandom() returns no more than 32 MiB as an int on Linux. Doesn’t that mean 
you can rely on syscall()’s long return value fitting in an int? Maybe just 
cast n = (int)sycall(...) to be explicit.

But it does make sense to cap n to LONG_MAX just in case there is some strange 
platform where it matters :)

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[issue27278] py_getrandom() uses an int for syscall() result

[STINNER Victor]

New submission from STINNER Victor:

syscall() result type is long.

Moreover, long type might can smaller than the size type, so we may need to add:

n = Py_MIN(size, LONG_MAX);

--
messages: 267969
nosy: haypo
priority: normal
severity: normal
status: open
title: py_getrandom() uses an int for syscall() result
versions: Python 3.5, Python 3.6

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