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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - Spurious -Wsign-conversion warning due to excessively clever glibc <sys/resource.h>"
href="http://llvm.org/bugs/show_bug.cgi?id=20742">20742</a>
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<th>Summary</th>
<td>Spurious -Wsign-conversion warning due to excessively clever glibc <sys/resource.h>
</td>
</tr>
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<th>Product</th>
<td>clang
</td>
</tr>
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<th>Version</th>
<td>unspecified
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>Linux
</td>
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<th>Status</th>
<td>NEW
</td>
</tr>
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<th>Severity</th>
<td>normal
</td>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>Frontend
</td>
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
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<th>Reporter</th>
<td>zackw@panix.com
</td>
</tr>
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<th>CC</th>
<td>llvmbugs@cs.uiuc.edu
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>This test program ...
#define _GNU_SOURCE
#include <sys/resource.h>
int spurious_sign_conversion_warning(int r, struct rlimit *l)
{
return setrlimit(r, l);
}
... produces a spurious -Wsign-conversion warning when compiled against
recent GNU libc's headers:
$ clang-3.5 -Wsign-conversion -c setrlimit.c
setrlimit.c:6:22: warning: implicit conversion changes signedness: 'int' to
'__rlimit_resource_t' (aka 'enum __rlimit_resource')
[-Wsign-conversion]
return setrlimit(r, l);
~~~~~~~~~ ^
1 warning generated.
The problem is this construct in <sys/resource.h>:
/* The X/Open standard defines that all the functions below must use
`int' as the type for the first argument. When we are compiling with
GNU extensions we change this slightly to provide better error
checking. */
#if defined __USE_GNU && !defined __cplusplus
typedef enum __rlimit_resource __rlimit_resource_t;
typedef enum __rusage_who __rusage_who_t;
typedef enum __priority_which __priority_which_t;
#else
typedef int __rlimit_resource_t;
typedef int __rusage_who_t;
typedef int __priority_which_t;
#endif
`enum __rlimit_resource` has no negative values and is therefore (I presume)
assigned an unsigned type, triggering the warning.
I don't think I should have to work around this in my code. X/Open says the
type of `setrlimit`'s first argument is `int`, therefore `RLIM_*` constants
should be passed around in `int` variables. Moreover, I don't see that there
*is* any workaround available to me in C that wouldn't harm portability to
other systems. (A portable program can reasonably want to define `_GNU_SOURCE`
in order to take advantage of specific glibc features when available.)
I initially filed this as a bug with Debian's glibc (
<a href="https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=758911">https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=758911</a> ) and was asked to
file an upstream clang bug inviting you to work with upstream glibc to resolve
this in a mutually satisfactory way. I will also file an upstream glibc bug
report and add the URL here.</pre>
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