Date: Fri, 16 Jan 2009 02:35:59 -0800 From: Garrett Cooper <yanefbsd@gmail.com> To: Christoph Mallon <christoph.mallon@gmx.de> 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: <7d6fde3d0901160235o6aa1f096q11c5096b70f3577@mail.gmail.com> In-Reply-To: <49705FA2.2020605@gmx.de> References: <7d6fde3d0901160041n55466290l55f737d274a40895@mail.gmail.com> <49704AEC.3080709@gmx.de> <200901161039.00232.christian.kandeler@hob.de> <49705FA2.2020605@gmx.de>
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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) !=3D 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) =A77.5:3.
>
>> 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) !=3D 0) {
o_errno =3D 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) !=3D 0) {
o_errno =3D 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 ~]$
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