Bug 330180

Summary:	False positive in v4l2?
Product:	[Developer tools] valgrind	Reporter:	João M. S. Silva <joao.m.santos.silva>
Component:	memcheck	Assignee:	Julian Seward <jseward>
Status:	RESOLVED NOT A BUG
Severity:	minor	CC:	tom
Priority:	NOR
Version First Reported In:	3.8.0
Target Milestone:	---
Platform:	Ubuntu
OS:	Linux
Latest Commit:		Version Fixed/Implemented In:
Sentry Crash Report:
Attachments:	reduced testcase

Description João M. S. Silva 2014-01-20 01:10:26 UTC

valgrind backtrace:

==23951== Syscall param ioctl(generic) points to uninitialised byte(s)
==23951==    at 0x43F7FB7: syscall (syscall.S:30)
==23951==    by 0x404D784: v4l2_fd_open (in /usr/lib/i386-linux-gnu/libv4l2.so.0)
==23951==    by 0x8049DE8: main (main.c:8)
==23951==  Address 0xbe870b58 is on thread 1's stack

gdb backtrace:

#0  0x04001172 in _dl_sysinfo_int80 () from /lib/ld-linux.so.2
#1  0x043e1fb7 in syscall () at ../sysdeps/unix/sysv/linux/i386/syscall.S:29
#2  0x0404d785 in v4l2_fd_open () from /usr/lib/i386-linux-gnu/libv4l2.so.0
#3  0x0404dc7e in v4l2_open () from /usr/lib/i386-linux-gnu/libv4l2.so.0
#4  0x0804b09a in v4l_capture () at v4l_capture.c:67
#5  0x08049de9 in main () at main.c:8

Relevant C code:

int fd = -1;
const char *dev_name = "/dev/video0";
fd = v4l2_open(dev_name, O_RDWR | O_NONBLOCK, 0);


Reproducible: Always




I think this was reported downstream here: https://bugs.launchpad.net/ubuntu/+source/libv4l/+bug/432477

The suggestion was to report upstream, which is what I'm doing since I get the same error and I don't see it reported in Valgrind.

Comment 1 João M. S. Silva 2014-01-20 01:11:53 UTC

Created attachment 84737 [details]
reduced testcase

Comment 2 Tom Hughes 2014-01-20 07:15:23 UTC

It's impossible to say if it's a false positive without examining the source of v4l2_open to see what it is doing.

It may be that valgrind needs better support for whatever ioctl it is doing - currently the "generic" handler is being used rather than a custom handler for that ioctl.

if you're not able to examine the v4l2 source yourself then I suggest you refer this to the v4l2 developers who will be able to determine if it's a bug in their code or a problem with valgrind, and if the latter will be able to provide more information.

Comment 3 Julian Seward 2014-05-09 14:29:27 UTC

João, please feel free to reopen if you have more information about
this ioctl.