Date: Fri, 16 Jan 2009 12:00:53 +0100 From: Christoph Mallon <christoph.mallon@gmx.de> To: Garrett Cooper <yanefbsd@gmail.com> Cc: Christian Kandeler <christian.kandeler@hob.de>, freebsd-hackers@freebsd.org Subject: Re: Confused by segfault with legitimate call to strerror(3) on amd64 / sysctl (3) setting `odd' errno's Message-ID: <497068E5.1050903@gmx.de> In-Reply-To: <7d6fde3d0901160235o6aa1f096q11c5096b70f3577@mail.gmail.com> References: <7d6fde3d0901160041n55466290l55f737d274a40895@mail.gmail.com> <49704AEC.3080709@gmx.de> <200901161039.00232.christian.kandeler@hob.de> <49705FA2.2020605@gmx.de> <7d6fde3d0901160235o6aa1f096q11c5096b70f3577@mail.gmail.com>
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Garrett Cooper schrieb:
> On Fri, Jan 16, 2009 at 2:21 AM, Christoph Mallon
> <christoph.mallon@gmx.de> wrote:
>> Christian Kandeler schrieb:
>>> On Friday 16 January 2009 09:53, Christoph Mallon wrote:
>>>
>>>>> int
>>>>> main() {
>>>>>
>>>>> int mib[4];
>>>>>
>>>>> size_t len;
>>>>>
>>>>> if (sysctlnametomib("kern.ipc.shmmax", mib, &len) != 0) {
>>>>> printf("Errno: %d\n", errno);
>>>>> errx(errno, "Error: %s", strerror(errno));
>>>> The use of errno is wrong. printf might change errno.
>>> I don't think printf() can set errno. And even if it could, it
>> Of course it can. See ISO/IEC 9899:1999 (E) §7.5:3.
>>
>>> wouldn't matter, because C has call-by-value semantics.
>> This has nothing to do with call-by-value. errno is read (even twice!)
>> *after* the call to printf().
>
> Ok, I just installworld'ed, recompiled the program with the
> following modifications, and I still get segfaults. And the question
> of the night is: why amd64 on a VERY recent CURRENT?
> I'm going to try the same app on an amd64 freebsd VMware instance
> with RELENG_7.
> Remember: just because a bunch of other people aren't reporting
> issues with CURRENT/amd64 doesn't mean that it isn't environmental,
> related to my hardware or compile options ;).
> Cheers,
> -Garrett
>
> #include <errno.h>
> #include <stdio.h>
> #include <sys/stat.h>
>
> int
> main()
> {
>
> struct stat sb;
>
> int o_errno;
>
> if (stat("/some/file/that/doesn't/exist", &sb) != 0) {
> o_errno = errno;
> printf("Errno: %d\n", errno);
> printf("%s\n", strerror(o_errno));
> }
>
> return 0;
>
> }
>
> #include <errno.h>
> #include <stdio.h>
> #include <sys/stat.h>
>
> int
> main()
> {
>
> struct stat sb;
>
> int o_errno;
>
> if (stat("/some/file/that/doesn't/exist", &sb) != 0) {
> o_errno = errno;
> printf("Errno: %d\n", errno);
> printf("%s\n", strerror(o_errno));
> }
>
> return 0;
>
> }
>
> [gcooper@optimus ~]$ gcc -o badfile badfile.c
> [gcooper@optimus ~]$ ./badfile
> Errno: 2
> Segmentation fault: 11 (core dumped)
> [gcooper@optimus ~]$
Compile with -Wall (you ALWAYS should do that) and then you'll see what
the problem is.
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