i use the newlib (standart, not newlib nano) that comes within atollic 8.1.
currently all kinds of XXXprintf versions corrupt my stack and i cant see why.
i have added 3 images to display the problem:
use case 1
in image 3.png, you see either vsprintf (rt_vsnprintf ist just a macro forward delaring it) that writes max. 1024 to "sBuf.printf_buffer" which is 1024 bytes long and located at 0x20001c08 (to 0x20002008).
by doing so, the newlib printf functions overwrite at least 1 variable of mine located at 0x20006014, so its not just a overflow by a bit, its quite off....
i tested with sprintf, snprintf, vsnprintf, vsprintf. all those functions write in my variable.
has someone an idea how such behavior could occur?
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The printf-functions require quite a bit of stack space. How big is your stack, and where is it located? Is it close to your canary variable at address 0x20006014? Could you try making the stack 2 kB bigger and see if there's a difference?
Related
When monitoring memory using the :C XXXX option, the memory values do not show when debugging. You can monitor up to 4000 characters by using the :C option when monitoring memory:
I have ran into this problem twice now. I am using IBM Rational Developer for i Version: 9.6.0.0, with the Java JDK/JRE v8u45.
Here are the values when debugging, and my data structure definition:
dcl-ds dsSQL qualified inz;
fullStmt varchar( 9360 ) inz;
end-ds;
Once I click on the element, all I see is ``. There is nothing in the value but that, but you can clearly see that dsSQL.fullStmt is not empty. I use this option daily and 99.99% of the time it works fine. I have to restart a million times, reset RDi to start with -c and recompile the program over and over to get it to work right.
Anyone have any idea how to fix this? I would give you the 'Error Log' but it is constantly filled and nothing in there seems to point to that issue. When adding or looking at that variable during debug, no errors are thrown.
You probably want to update to the latest 9.6.0.6 release. They have fixed at least a few memory problems with the debugger between your release and the latest.
https://www-01.ibm.com/support/docview.wss?uid=swg27038481
We have an application software running on Suse linux. What I want is that whenever there is a crash/fault in the software, a backtrace is generated with call stack information for the current thread(which faults).
We are currently using "backtrace()" and "backtrace_symbols_fd()" to try to get the trace but there is not much useful information. It does not give function names, line no. and filename.
Therefore, I starting looking for alternate options to use and found "libunwind". Wrote a small function to get backtrace and it does print function name with other register values(ip,sp). But still I can not get the filename and linenumbers. Is there a way I can programmatically do that ? What happens if I strip my binary file? Can I still get the filename/lineno info ?
I want to add custom syscall to freebsd(school work). I google hundreds of time. there is no right solution for it.
my homework is: "Add custom syscall to freebsd kernel and recompile the kernel and use it".
finally I find that I should follow instructions in these two pages:
1 : http://www.onlamp.com/pub/a/bsd/2003/10/09/adding_system_calls.html
then
2: https://www.freebsd.org/doc/en/books/handbook/kernelconfig-building.html
will it shows errors in compile time:
<sys/parma.h> no such file or directory
<sys/kern.h> no such file or directory
<sys/syscallargs.h> no such file or directory
I removed these three header include form my file then recompile it. now shows other errors like: MAXCPU undeclered in pcpu.h file.
what I missed? how can I do my school work?
NOTE: I use freebsd8 in vbox
Look at what the error messages say; the files don't exist.
The first include file is a typo; it's param.h, not parma.h!
There is no kern.h. Maybe you mean sys/kernel.h?
Idem for syscallargs.h. Do you perhaps mean syscall.h?
You can find header files with e.g:
find /usr/src/sys/ -type f -name '*.h'|grep 'sys/.*kern.*\.h'
/usr/src/sys/ofed/include/linux/kernel.h
/usr/src/sys/dev/netmap/netmap_kern.h
...
Update: More important is determining which includes you actually need.
FreeBSD has pretty good documentation. If you want to use a kernel function or data-structure, it is probably covered in section 9 of the manual pages.
You can list all the manual pages in that section with ls /usr/share/man/man9/ | less. Or you can use the apropos command.
Since you want to implement a syscall, start with e.g.
apropos syscall
It will return:
SYSCALL_MODULE(9) - syscall kernel module declaration macro
syscall(2), __syscall(2) - indirect system call
It seems to me that the first one could be relevant to your assignment. (The second one is how to call a system call from user space.) So read it with man SYSCALL_MODULE. Or read it online.
Note that:
A minimal example for a syscall module can be found in
/usr/share/examples/kld/syscall/module/syscall.c.
That example should be enough to get you started on writing your own system call module...
Well take a look at share/examples/kld/syscall for a complete implementation as a module.
Adding a new file to teh kernel is left as an exercise for the reader.
Here is a hint: find the newest added file within kern/* subdir AND CHECK WHAT COMMITS WERE DONE TO MAKE IT COMPILE.
In fact you could have done exactly the same with syscall: FIND THE NEWEST ADDED SYSCALL AND CHECK HOW IT WAS ACHIEVED.
All this is available in svn/git repository history.
On Ubuntu 12.04 I am tring to get the subtree of management values with the following command:
snmpwalk -v 2c -c public localhost
with the last line of the output being
iso.3.6.1.2.1.25.1.7.0 = No more variables left in this MIB View (It is past the end of the MIB tree)
Is this an error? A warning? Does the subtree end there?
There's a bit more going on here than you might suspect. I encounter this on every new Ubuntu box that I build, and I do consider it a problem (not an error, but a problem--more on this down further).
Here's the technically-correct explanation (why this is not an "error"):
"No more variables left in this MIB View" is not particularly an error; rather, it is a statement about your request. The request started at something simple, say ".1.3" and continued to ask for the "next" lexicographic OID. It got "next" OIDs until that last one, at which point the agent has informed you that there's nothing more to see; don't bother asking.
Now, here's why I consider it a problem (in the context of this question):
The point of installing "snmpd" and running it is to gather meaningful information about the box; typically, this information is performance-oriented. For example, the three general things that I need to know about are network-interface information (IF-MIB::ifHCInOctets and IF-MIB::ifHCOutOctets), disk information (UCD-SNMP-MIB::dskUsed and UCD-SNMP-MIB::dskTotal), and CPU information (UCD-SNMP-MIB::ssCpuRawIdle, UCD-SNMP-MIB::ssCpuRawWait, and so on).
The default Ubuntu "snmpd" configuration specifically denies just about everything useful with this configuration (limiting access to just enough information to tell you that the box is a Linux box):
view systemonly included .1.3.6.1.2.1.1
view systemonly included .1.3.6.1.2.1.25.1
rocommunity public default -V systemonly
This configuration locks the box down, which may be "safe" if it will be on an insecure network with little SNMP administration knowledge available.
However, the first thing that I do is remove the "-V systemonly" portion of the "rocommunity" setting; this will allow all available SNMP information to be accessed (read-only) via the community string of "public".
If you do that, then you'll probably see what you're expecting, which is pages and pages of SNMP information that you can use to gauge the performance of your box.
I know this thread is probably very old the I fix this is to use:
rocommunity public
and that should fix the problem.
Briefly, this is not an error, actually, when you "walk up" all OIDs on your agent, it will shows your this line>
Sometimes, it won't show you this line, because the last OID is not on your agent(you have already walk up all OIDs on your agent, but not walk up all OIDs).
$ snmpwalk -v 2c -c public localhost NET-SNMP-EXTEND-MIB::nsExtendObjects
NET-SNMP-EXTEND-MIB::nsExtendObjects = No more variables left in this MIB View (It is past the end of the MIB tree)
Also you can get this error while you can trying to see executed scripts I fix that problem to add
view all included .1 80
line to snmpd.conf than restart service
Than you will see your output going to change for both input
I am using a command in the proc file system which is the following
echo 0 > /proc/sys/net/ipv4/ip_forward
Note: I don't want to know the basic of the command written above, I want what all happens when it goes inside the kernel. As, I want to implement one of the /proc file.
Now if I want to trace the code right from when the 0 is echoed in the file-system then how to go about it. I mean if I want to trace what happens when I do this.
I want to see where in the kernel code this 0 is accepted and in which value does it get stored inorder to make the changes. Please, can somebody tell what all happens when you call this command. I want in detail explain. I don't want the description of the command.
Any related article on how it changes the kernel parameters is also fine.
I have read this but, not explained there. http://www.linuxjournal.com/article/8381
Thanks
search through linux tree (especially network stack) for create_proc_entry function. Figure out what file creates ip_forward (it must be in ip4v drivers) from name passed to create_proc_entry.
When you find the file, look at where proc_dir_entry structure is created and what functions are assigned to its read_proc, write_proc members.