Re: Confused by segfault with legitimate call to strerror(3) on amd64 / sysctl(3) setting `odd' errno's
Garrett Cooper yanef...@gmail.com writes: #include err.h #include errno.h #include stdio.h #include sys/types.h #include sys/sysctl.h You should always put your sys includes before your non-sys includes, and in any case, sys/types.h should always come first. printf(Errno: %d\n, errno); errx(errno, Error: %s, strerror(errno)); In addition to what everybody else said, errno is not an appropriate value for errx's first argument. Use 1 or EXIT_FAILURE (or one of the macros defined in sysexits.h, but I wouldn't recommend it). Also, you probably want to use err(), not errx(), and *always* compile with -Wall -Wextra, and unless you're going to run gdb on your program, -O2 (which enables additional code analysis) DES -- Dag-Erling Smørgrav - d...@des.no ___ freebsd-hackers@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-hackers To unsubscribe, send any mail to freebsd-hackers-unsubscr...@freebsd.org
Re: Confused by segfault with legitimate call to strerror(3) on amd64 / sysctl(3) setting `odd' errno's
Hi Garrett,
On Fri, 16 Jan 2009, Garrett Cooper wrote:
On Fri, Jan 16, 2009 at 12:58 AM, Garrett Cooper yanef...@gmail.com wrote:
On Fri, Jan 16, 2009 at 12:57 AM, Christoph Mallon
christoph.mal...@gmx.de wrote:
Garrett Cooper schrieb:
Good point. I modified the source to do that.
Thanks,
-Garrett
You should reply to all so the discussion stays on the list.
Yeah, that was a goofup on my part. Go-go Gmail web interface!
-Garrett
Hmmm... looks like the strerror issue it could be a serious bug:
Add #include string.h.
Without it you don't get the strerror() prototype, so the return value
defaults to an int. Thus the compiler will truncate the pointer value
to junk. The crash happens when formatting the output.
Compile with -Wall and pay attention to warnings (or use -Werror)
to catch these things.
$.02,
/Mikko
#include errno.h
#include stdio.h
#include sys/stat.h
int
main()
{
struct stat sb;
int o_errno;
if (stat(/some/file/that/doesn't/exist, sb) != 0) {
o_errno = errno;
printf(Errno: %d\n, errno);
err(errno, %s, strerror(o_errno));
}
return 0;
}
[gcoo...@optimus ~]$ ./badfile
Errno: 2
badfile: Segmentation fault: 11 (core dumped)
I rebuilt my kernel and installed it, and I rebuilt world, but
haven't installed it yet though, so let me reboot the amd64 machine
and see what happens (may be a mismatched ABI issue)...
Cheers,
-Garrett
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Re: Confused by segfault with legitimate call to strerror(3) on amd64 / sysctl(3) setting `odd' errno's
On Fri, Jan 16, 2009 at 12:41 AM, Garrett Cooper yanef...@gmail.com wrote:
Hi amd64 and Hackers,
Uh, I'm really confused why 1) this error (errno = ENOMEM) would
occur when I have more than enough free memory (both on x86 and amd64)
and 2) why strerror would segfault in the call to errx in the attached
sourcefile on amd64 only. Not initializing len causes the second
output sample (errno = 14, which is EFAULT).
Any ideas?
Please CC me if mailing on amd64@ as I'm not subscribed to the list.
Thanks,
-Garrett
/* Program */
#include err.h
#include errno.h
#include stdio.h
#include sys/types.h
#include sys/sysctl.h
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));
}
printf(%lu\n, len);
return 0;
}
# output for len preset to 0:
[gcoo...@optimus ~]$ ./test2
Errno: 12
test2: Segmentation fault: 11 (core dumped)
[gcoo...@optimus ~]$ uname -a
FreeBSD optimus.gateway.2wire.net 8.0-CURRENT FreeBSD 8.0-CURRENT #4:
Sun Jan 11 12:30:31 PST 2009
r...@optimus.gateway.2wire.net:/usr/obj/usr/src/sys/OPTIMUS amd64
[gcoo...@orangebox /usr/home/gcooper]$ ./test
Errno: 12
test: Error: Cannot allocate memory
[gcoo...@orangebox /usr/home/gcooper]$ uname -a
FreeBSD orangebox.gateway.2wire.net 8.0-CURRENT FreeBSD 8.0-CURRENT
#4: Sat Jan 3 22:54:52 PST 2009
gcoo...@orangebox.gateway.2wire.net:/usr/obj/usr/src/sys/ORANGEBOX
i386
# output for len not preset to 0:
[gcoo...@optimus ~]$ ./test2
Errno: 14
test2: Segmentation fault: 11 (core dumped)
Almost forgot -- here are the actual values reported by sysctl(1),
just for reference:
[gcoo...@optimus ~]$ sysctl kern.ipc.shmall kern.ipc.shmmin kern.ipc.shmmax
kern.ipc.shmall: 8192
kern.ipc.shmmin: 1
kern.ipc.shmmax: 33554432
[gcoo...@orangebox /usr/src/sys]$ sysctl kern.ipc.shmall
kern.ipc.shmmin kern.ipc.shmmax
kern.ipc.shmall: 8192
kern.ipc.shmmin: 1
kern.ipc.shmmax: 33554432
Thanks,
-Garrett
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Re: Confused by segfault with legitimate call to strerror(3) on amd64 / sysctl(3) setting `odd' errno's
Garrett Cooper schrieb:
Hi amd64 and Hackers,
Uh, I'm really confused why 1) this error (errno = ENOMEM) would
occur when I have more than enough free memory (both on x86 and amd64)
and 2) why strerror would segfault in the call to errx in the attached
sourcefile on amd64 only. Not initializing len causes the second
output sample (errno = 14, which is EFAULT).
Any ideas?
Please CC me if mailing on amd64@ as I'm not subscribed to the list.
Thanks,
-Garrett
len is not uninitialised. This leads to undefined behaviour. Anything
can happen. Probably the syscall overwrites parts of the stack because
len has some (random) high value.
/* Program */
#include err.h
#include errno.h
#include stdio.h
#include sys/types.h
#include sys/sysctl.h
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. Store the errno
into a local variable before you do any call, which might modify it.
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Re: Confused by segfault with legitimate call to strerror(3) on amd64 / sysctl(3) setting `odd' errno's
On Fri, Jan 16, 2009 at 12:47 AM, Jacques Fourie jacques.fou...@gmail.com wrote: You need to initialize len to the number of entries in the mib array. Try adding 'len = 4' before calling sysctlnametomib() and see if your issues go away. Ok, that solution works (I think). So, problem 2 down. Now: what about the segfaulting strerror(3) call on amd64 ;\? -Garrett ___ freebsd-hackers@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-hackers To unsubscribe, send any mail to freebsd-hackers-unsubscr...@freebsd.org
Re: Confused by segfault with legitimate call to strerror(3) on amd64 / sysctl(3) setting `odd' errno's
On Fri, 16 Jan 2009, 00:44-0800, Garrett Cooper wrote: On Fri, Jan 16, 2009 at 12:41 AM, Garrett Cooper yanef...@gmail.com wrote: Hi amd64 and Hackers, Uh, I'm really confused why 1) this error (errno = ENOMEM) would occur when I have more than enough free memory (both on x86 and amd64) and 2) why strerror would segfault in the call to errx in the attached sourcefile on amd64 only. Not initializing len causes the second output sample (errno = 14, which is EFAULT). Any ideas? - size_t len; + size_t len = 4; -- Maxim Konovalov ___ freebsd-hackers@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-hackers To unsubscribe, send any mail to freebsd-hackers-unsubscr...@freebsd.org
Re: Confused by segfault with legitimate call to strerror(3) on amd64 / sysctl(3) setting `odd' errno's
On Fri, Jan 16, 2009 at 10:47 AM, Jacques Fourie
jacques.fou...@gmail.com wrote:
On Fri, Jan 16, 2009 at 10:44 AM, Garrett Cooper yanef...@gmail.com wrote:
On Fri, Jan 16, 2009 at 12:41 AM, Garrett Cooper yanef...@gmail.com wrote:
Hi amd64 and Hackers,
Uh, I'm really confused why 1) this error (errno = ENOMEM) would
occur when I have more than enough free memory (both on x86 and amd64)
and 2) why strerror would segfault in the call to errx in the attached
sourcefile on amd64 only. Not initializing len causes the second
output sample (errno = 14, which is EFAULT).
Any ideas?
Please CC me if mailing on amd64@ as I'm not subscribed to the list.
Thanks,
-Garrett
/* Program */
#include err.h
#include errno.h
#include stdio.h
#include sys/types.h
#include sys/sysctl.h
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));
}
printf(%lu\n, len);
return 0;
}
# output for len preset to 0:
[gcoo...@optimus ~]$ ./test2
Errno: 12
test2: Segmentation fault: 11 (core dumped)
[gcoo...@optimus ~]$ uname -a
FreeBSD optimus.gateway.2wire.net 8.0-CURRENT FreeBSD 8.0-CURRENT #4:
Sun Jan 11 12:30:31 PST 2009
r...@optimus.gateway.2wire.net:/usr/obj/usr/src/sys/OPTIMUS amd64
[gcoo...@orangebox /usr/home/gcooper]$ ./test
Errno: 12
test: Error: Cannot allocate memory
[gcoo...@orangebox /usr/home/gcooper]$ uname -a
FreeBSD orangebox.gateway.2wire.net 8.0-CURRENT FreeBSD 8.0-CURRENT
#4: Sat Jan 3 22:54:52 PST 2009
gcoo...@orangebox.gateway.2wire.net:/usr/obj/usr/src/sys/ORANGEBOX
i386
# output for len not preset to 0:
[gcoo...@optimus ~]$ ./test2
Errno: 14
test2: Segmentation fault: 11 (core dumped)
Almost forgot -- here are the actual values reported by sysctl(1),
just for reference:
[gcoo...@optimus ~]$ sysctl kern.ipc.shmall kern.ipc.shmmin kern.ipc.shmmax
kern.ipc.shmall: 8192
kern.ipc.shmmin: 1
kern.ipc.shmmax: 33554432
[gcoo...@orangebox /usr/src/sys]$ sysctl kern.ipc.shmall
kern.ipc.shmmin kern.ipc.shmmax
kern.ipc.shmall: 8192
kern.ipc.shmmin: 1
kern.ipc.shmmax: 33554432
Thanks,
-Garrett
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You need to initialize len to the number of entries in the mib array.
Try adding 'len = 4' before calling sysctlnametomib() and see if your
issues go away.
Sorry, I only scanned through the code without reading the whole
message before replying :) Please ignore...
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Re: Confused by segfault with legitimate call to strerror(3) on amd64 / sysctl(3) setting `odd' errno's
On Fri, Jan 16, 2009 at 12:57 AM, Christoph Mallon christoph.mal...@gmx.de wrote: Garrett Cooper schrieb: Good point. I modified the source to do that. Thanks, -Garrett You should reply to all so the discussion stays on the list. Yeah, that was a goofup on my part. Go-go Gmail web interface! -Garrett ___ freebsd-hackers@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-hackers To unsubscribe, send any mail to freebsd-hackers-unsubscr...@freebsd.org
Re: Confused by segfault with legitimate call to strerror(3) on amd64 / sysctl(3) setting `odd' errno's
On Fri, Jan 16, 2009 at 10:44 AM, Garrett Cooper yanef...@gmail.com wrote:
On Fri, Jan 16, 2009 at 12:41 AM, Garrett Cooper yanef...@gmail.com wrote:
Hi amd64 and Hackers,
Uh, I'm really confused why 1) this error (errno = ENOMEM) would
occur when I have more than enough free memory (both on x86 and amd64)
and 2) why strerror would segfault in the call to errx in the attached
sourcefile on amd64 only. Not initializing len causes the second
output sample (errno = 14, which is EFAULT).
Any ideas?
Please CC me if mailing on amd64@ as I'm not subscribed to the list.
Thanks,
-Garrett
/* Program */
#include err.h
#include errno.h
#include stdio.h
#include sys/types.h
#include sys/sysctl.h
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));
}
printf(%lu\n, len);
return 0;
}
# output for len preset to 0:
[gcoo...@optimus ~]$ ./test2
Errno: 12
test2: Segmentation fault: 11 (core dumped)
[gcoo...@optimus ~]$ uname -a
FreeBSD optimus.gateway.2wire.net 8.0-CURRENT FreeBSD 8.0-CURRENT #4:
Sun Jan 11 12:30:31 PST 2009
r...@optimus.gateway.2wire.net:/usr/obj/usr/src/sys/OPTIMUS amd64
[gcoo...@orangebox /usr/home/gcooper]$ ./test
Errno: 12
test: Error: Cannot allocate memory
[gcoo...@orangebox /usr/home/gcooper]$ uname -a
FreeBSD orangebox.gateway.2wire.net 8.0-CURRENT FreeBSD 8.0-CURRENT
#4: Sat Jan 3 22:54:52 PST 2009
gcoo...@orangebox.gateway.2wire.net:/usr/obj/usr/src/sys/ORANGEBOX
i386
# output for len not preset to 0:
[gcoo...@optimus ~]$ ./test2
Errno: 14
test2: Segmentation fault: 11 (core dumped)
Almost forgot -- here are the actual values reported by sysctl(1),
just for reference:
[gcoo...@optimus ~]$ sysctl kern.ipc.shmall kern.ipc.shmmin kern.ipc.shmmax
kern.ipc.shmall: 8192
kern.ipc.shmmin: 1
kern.ipc.shmmax: 33554432
[gcoo...@orangebox /usr/src/sys]$ sysctl kern.ipc.shmall
kern.ipc.shmmin kern.ipc.shmmax
kern.ipc.shmall: 8192
kern.ipc.shmmin: 1
kern.ipc.shmmax: 33554432
Thanks,
-Garrett
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You need to initialize len to the number of entries in the mib array.
Try adding 'len = 4' before calling sysctlnametomib() and see if your
issues go away.
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Re: Confused by segfault with legitimate call to strerror(3) on amd64 / sysctl(3) setting `odd' errno's
On Fri, Jan 16, 2009 at 12:58 AM, Garrett Cooper yanef...@gmail.com wrote:
On Fri, Jan 16, 2009 at 12:57 AM, Christoph Mallon
christoph.mal...@gmx.de wrote:
Garrett Cooper schrieb:
Good point. I modified the source to do that.
Thanks,
-Garrett
You should reply to all so the discussion stays on the list.
Yeah, that was a goofup on my part. Go-go Gmail web interface!
-Garrett
Hmmm... looks like the strerror issue it could be a serious bug:
#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);
err(errno, %s, strerror(o_errno));
}
return 0;
}
[gcoo...@optimus ~]$ ./badfile
Errno: 2
badfile: Segmentation fault: 11 (core dumped)
I rebuilt my kernel and installed it, and I rebuilt world, but
haven't installed it yet though, so let me reboot the amd64 machine
and see what happens (may be a mismatched ABI issue)...
Cheers,
-Garrett
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Re: Confused by segfault with legitimate call to strerror(3) on amd64 / sysctl(3) setting `odd' errno's
Garrett Cooper schrieb:
On Fri, Jan 16, 2009 at 12:58 AM, Garrett Cooper yanef...@gmail.com wrote:
On Fri, Jan 16, 2009 at 12:57 AM, Christoph Mallon
christoph.mal...@gmx.de wrote:
Garrett Cooper schrieb:
Good point. I modified the source to do that.
Thanks,
-Garrett
You should reply to all so the discussion stays on the list.
Yeah, that was a goofup on my part. Go-go Gmail web interface!
-Garrett
Hmmm... looks like the strerror issue it could be a serious bug:
#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);
err(errno, %s, strerror(o_errno));
You are still using the wrong errno.
Also err() itself prints the error string using strerror(). There might
be some interference when the result of one call to strerror() (your
call) is used after another call to strerror() (err() internally).
I doubt there is a bug in the library, otherwise we would see many
bugreports of segfaults on AMD64.
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Re: Confused by segfault with legitimate call to strerror(3) on amd64 / sysctl (3) setting `odd' errno's
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
wouldn't matter, because C has call-by-value semantics.
Christian
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Re: Confused by segfault with legitimate call to strerror(3) on amd64 / sysctl (3) setting `odd' errno's
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().
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Re: Confused by segfault with legitimate call to strerror(3) on amd64 / sysctl (3) setting `odd' errno's
On Fri, Jan 16, 2009 at 2:21 AM, Christoph Mallon
christoph.mal...@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;
}
[gcoo...@optimus ~]$ gcc -o badfile badfile.c
[gcoo...@optimus ~]$ ./badfile
Errno: 2
Segmentation fault: 11 (core dumped)
[gcoo...@optimus ~]$
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Re: Confused by segfault with legitimate call to strerror(3) on amd64 / sysctl (3) setting `odd' errno's
On Fri, Jan 16, 2009 at 2:35 AM, Garrett Cooper yanef...@gmail.com wrote:
On Fri, Jan 16, 2009 at 2:21 AM, Christoph Mallon
christoph.mal...@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
Ugh... I pasted it twice by accident. Sorry.
-Garrett
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Re: Confused by segfault with legitimate call to strerror(3) on amd64 / sysctl (3) setting `odd' errno's
Garrett Cooper schrieb:
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;
}
[gcoo...@optimus ~]$ gcc -o badfile badfile.c
[gcoo...@optimus ~]$ ./badfile
Errno: 2
Segmentation fault: 11 (core dumped)
[gcoo...@optimus ~]$
Well, compile with -g, start in gdb, check what value is wrong, the
usual stuff. Probably the return value of strerror() is interesting.
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Re: Confused by segfault with legitimate call to strerror(3) on amd64 / sysctl (3) setting `odd' errno's
Garrett Cooper schrieb:
On Fri, Jan 16, 2009 at 2:21 AM, Christoph Mallon
christoph.mal...@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;
}
[gcoo...@optimus ~]$ gcc -o badfile badfile.c
[gcoo...@optimus ~]$ ./badfile
Errno: 2
Segmentation fault: 11 (core dumped)
[gcoo...@optimus ~]$
Compile with -Wall (you ALWAYS should do that) and then you'll see what
the problem is.
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Re: Confused by segfault with legitimate call to strerror(3) on amd64 / sysctl (3) setting `odd' errno's
Garrett Cooper schrieb:
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;
}
[gcoo...@optimus ~]$ gcc -o badfile badfile.c
[gcoo...@optimus ~]$ ./badfile
Errno: 2
Segmentation fault: 11 (core dumped)
[gcoo...@optimus ~]$
Well, compile with -g, start in gdb, check what value is wrong, the
usual stuff. Probably the return value of strerror() is interesting.
some facts:
#include stdio.h
int
main()
{
printf(%s\n, strerror(2));
return 0;
}
1- it works fine on i386
2- it bombs on amd64
3- with a local strerror.c (instead of the one in libc)
works fine
so, there is something realy wrong going on here!
(and it gows back to at least 7.0-stable)
danny
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Re: Confused by segfault with legitimate call to strerror(3) on amd64 / sysctl (3) setting `odd' errno's
Danny Braniss schrieb:
some facts:
#include stdio.h
int
main()
{
printf(%s\n, strerror(2));
return 0;
}
1- it works fine on i386
2- it bombs on amd64
3- with a local strerror.c (instead of the one in libc)
works fine
so, there is something realy wrong going on here!
(and it gows back to at least 7.0-stable)
No, everything is perfectly correct. I suggested this earlier: Compile
with -Wall and you'll see what the problem is.
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Re: Confused by segfault with legitimate call to strerror(3) on amd64 / sysctl (3) setting `odd' errno's
On Fri, Jan 16, 2009 at 01:33:38PM +0200, Danny Braniss wrote:
some facts:
#include stdio.h
int
main()
{
printf(%s\n, strerror(2));
return 0;
}
1- it works fine on i386
2- it bombs on amd64
3- with a local strerror.c (instead of the one in libc)
works fine
so, there is something realy wrong going on here!
(and it gows back to at least 7.0-stable)
The compiler thinks strerror returns an int. Include string.h.
ahh, RTFM ALL THE WAY! I just saw the top few lines:
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include stdio.h
but later it shows:
#include string.h
char *
strerror(int errnum);
on the other hand, compiling with -static workes ok, which sent me on
the wrong trail.
danny
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Re: Confused by segfault with legitimate call to strerror(3) on amd64 / sysctl (3) setting `odd' errno's
On Fri, Jan 16, 2009 at 01:33:38PM +0200, Danny Braniss wrote:
some facts:
#include stdio.h
int
main()
{
printf(%s\n, strerror(2));
return 0;
}
1- it works fine on i386
2- it bombs on amd64
3- with a local strerror.c (instead of the one in libc)
works fine
so, there is something realy wrong going on here!
(and it gows back to at least 7.0-stable)
The compiler thinks strerror returns an int. Include string.h.
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Re: Confused by segfault with legitimate call to strerror(3) on amd64 / sysctl (3) setting `odd' errno's
Le Friday 16 January 2009, Garrett Cooper a écrit :
On Fri, Jan 16, 2009 at 2:21 AM, Christoph Mallon
#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;
}
with this, it's better on an amd64/ RELENG_7 machine :
% diff -ub badfile.c.ori badfile.c
--- badfile.c.ori 2009-01-16 11:49:44.778991057 +0100
+++ badfile.c 2009-01-16 11:49:03.470465677 +0100
@@ -1,6 +1,7 @@
#include errno.h
#include stdio.h
#include sys/stat.h
+#include string.h
int
main()
Cheers
TfH
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Re: Confused by segfault with legitimate call to strerror(3) on amd64 / sysctl (3) setting `odd' errno's
On Fri, Jan 16, 2009 at 2:52 AM, Thierry Herbelot
thierry.herbe...@free.fr wrote:
Le Friday 16 January 2009, Garrett Cooper a écrit :
On Fri, Jan 16, 2009 at 2:21 AM, Christoph Mallon
#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;
}
with this, it's better on an amd64/ RELENG_7 machine :
% diff -ub badfile.c.ori badfile.c
--- badfile.c.ori 2009-01-16 11:49:44.778991057 +0100
+++ badfile.c 2009-01-16 11:49:03.470465677 +0100
@@ -1,6 +1,7 @@
#include errno.h
#include stdio.h
#include sys/stat.h
+#include string.h
int
main()
Cheers
TfH
That's hilarious -- why does it pass though without issue on x86 though?
-Garrett
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Re: Confused by segfault with legitimate call to strerror(3) on amd64 / sysctl (3) setting `odd' errno's
On Fri, 16 Jan 2009, Garrett Cooper wrote:
On Fri, Jan 16, 2009 at 2:52 AM, Thierry Herbelot
thierry.herbe...@free.fr wrote:
Le Friday 16 January 2009, Garrett Cooper a écrit :
On Fri, Jan 16, 2009 at 2:21 AM, Christoph Mallon
#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;
}
with this, it's better on an amd64/ RELENG_7 machine :
% diff -ub badfile.c.ori badfile.c
--- badfile.c.ori 2009-01-16 11:49:44.778991057 +0100
+++ badfile.c 2009-01-16 11:49:03.470465677 +0100
@@ -1,6 +1,7 @@
#include errno.h
#include stdio.h
#include sys/stat.h
+#include string.h
int
main()
Cheers
TfH
That's hilarious -- why does it pass though without issue on x86 though?
-Garrett
As pointed out, when you don't have a declaration for strerror, it's
implicitly assumed to return `int'. This feature was widely used in the
early days of C and so continues to be accepted by compilers, and gcc by
default doesn't warn about it.
On x86, int and char * are the same size. So even though the compiler
thinks strerror is returning an int which is being passed to printf, the
code it generates is the same as for a char *. On amd64, int is 32 bits
but char * is 64. When the compiler thinks it's using int, it only keeps
track of the lower 32 bits, and the upper 32 bits get zeroed. So the
pointer that printf receives has had its upper 32 bits zeroed, and no
longer points where it should. Hence segfault.
Since running on amd64 I've seen a lot of bugs where people carelessly
assume (perhaps without noticing) that ints and pointers are practically
interchangeable, which works on x86 and the like but breaks on amd64.
Variadic functions are special offenders because the compiler can't do
much type checking.
Pop quiz: which of the following statements is correct?
#include stdlib.h
#include unistd.h
execl(/bin/sh, /bin/sh, 0);
execl(/bin/sh, /bin/sh, NULL);
--
Nate Eldredge
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Re: Confused by segfault with legitimate call to strerror(3) on amd64 / sysctl (3) setting `odd' errno's
On Fri, Jan 16, 2009 at 10:33:15AM -0800, Nate Eldredge wrote: Pop quiz: which of the following statements is correct? #include stdlib.h #include unistd.h execl(/bin/sh, /bin/sh, 0); execl(/bin/sh, /bin/sh, NULL); None, as NULL is allowed to expand to 0. You have to write execl(/bin/sh, /bin/sh, (char *)0); ___ freebsd-hackers@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-hackers To unsubscribe, send any mail to freebsd-hackers-unsubscr...@freebsd.org
