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Date: Wed, 16 Jan 2019 11:06:55 -0800
From: Keith Thompson <keithsthompson@...il.com>
To: musl@...ts.openwall.com
Cc: Keith Thompson <Keith.S.Thompson@...il.com>
Subject: Minor C99 conformance issue: FILE is an incomplete type
The musl 1.0.0 manual says that it's intended to conform to C99.
Both the C99 and C11 standards require FILE to be an object type.
In C99, incomplete types are not object types. In C11, the definition
of "object type" was changed, so now incomplete types are object types.
(See section C99 and C11 6.2.5, C99 7.19.1, C11 7.21.1.)
So, in C99 FILE is not permitted to be an incomplete type, but in C11
it is. (The section describing type FILE did not change. I don't
know whether the authors of the standard actually intended to change
the requirement.)
Using musl-gcc, FILE is an incomplete type, so it conforms to C11
but not to C99. <stdio.h> could be modified so that, for example,
it pays attention to the value of __STDC_VERSION__ to decide how to
define FILE (whether to make struct _IO_FILE visible).
I do not suggest that this minor non-conformance to C99 is a practical
problem, or even that it should be fixed, merely that it should
be noted.
$ cat /etc/lsb-release
DISTRIB_ID=Ubuntu
DISTRIB_RELEASE=18.04
DISTRIB_CODENAME=bionic
DISTRIB_DESCRIPTION="Ubuntu 18.04.1 LTS"
$ uname -a
Linux bomb20 4.15.0-42-generic #45-Ubuntu SMP Thu Nov 15 19:32:57 UTC
2018 x86_64 x86_64 x86_64 GNU/Linux
$ dpkg -l musl
Desired=Unknown/Install/Remove/Purge/Hold
| Status=Not/Inst/Conf-files/Unpacked/halF-conf/Half-inst/trig-aWait/Trig-pend
|/ Err?=(none)/Reinst-required (Status,Err: uppercase=bad)
||/ Name Version
Architecture Description
+++-=========================================-=========================-=========================-=======================================================================================
ii musl:amd64 1.1.19-1
amd64 standard C library
$ gcc --version
gcc (Ubuntu 7.3.0-27ubuntu1~18.04) 7.3.0
Copyright (C) 2017 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
$ cat FILE_bug.c.
#include <stdio.h>
int main(void) {
printf("sizeof (FILE) = %zu\n", sizeof (FILE));
}
$ musl-gcc -std=c99 -c FILE_bug.c
FILE_bug.c: In function ‘main’:
FILE_bug.c:3:45: error: invalid application of ‘sizeof’ to
incomplete type ‘FILE {aka struct _IO_FILE}’
printf("sizeof (FILE) = %zu\n", sizeof (FILE));
^~~~
$ musl-gcc -std=c11 -c FILE_bug.c
FILE_bug.c: In function ‘main’:
FILE_bug.c:3:45: error: invalid application of ‘sizeof’ to
incomplete type ‘FILE {aka struct _IO_FILE}’
printf("sizeof (FILE) = %zu\n", sizeof (FILE));
^~~~
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