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bug#21694: 'clone' syscall binding unreliable

From: Mark H Weaver
Subject: bug#21694: 'clone' syscall binding unreliable
Date: Wed, 28 Oct 2015 00:53:28 -0400
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/24.5 (gnu/linux)

address@hidden (Ludovic Courtès) writes:

> Mark H Weaver <address@hidden> skribis:
>> address@hidden (Ludovic Courtès) writes:
> [...]
>>>  ;; The libc interface to sys_clone is not useful for Scheme programs, so 
>>> the
>>> -;; low-level system call is wrapped instead.
>>> +;; low-level system call is wrapped instead.  The 'syscall' function is
>>> +;; declared in <unistd.h> as a variadic function; in practice, it expects 6
>>> +;; pointer-sized arguments, as shown in, e.g., x86_64/syscall.S.
>>>  (define clone
>>>    (let* ((ptr        (dynamic-func "syscall" (dynamic-link)))
>>> -         (proc       (pointer->procedure int ptr (list int int '*)))
>>> +         (proc       (pointer->procedure long ptr
>>> +                                         (list long                   
>>> ;sysno
>>> +                                               unsigned-long          
>>> ;flags
>> 'long' and 'unsigned long' might not be the same size as a pointer.
>> Better to use 'size_t' for both of these.  While not strictly guaranteed
>> to be the same size as a pointer, in practice they should be the same
>> except on architectures with segmented memory models.
>> What do you think?
> I had the same reaction, but posix/unistd.h in libc really uses these
> types for ‘syscall’ so I thought it’d be best to stick to them.

Okay, makes sense.


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