How to include C backtrace in a kernel module code?

Question

So I am trying to find out what kernel processes are calling some functions in a block driver. I thought including backtrace() in the C library would make it easy. But I am having trouble to load the backtrace.

I copied this example function to show the backtrace:

http://www.linuxjournal.com/files/linuxjournal.com/linuxjournal/articles/063/6391/6391l1.html

All attempts to compile have error in one place or another that a file cannot be found or that the functions are not defined.

Here is what comes closest.

In the Makefile I put the compiler directives:

 -rdynamic -I/usr/include 

If I leave out the second one, -I/usr/include, then the compiler reports it cannot find the required header execinfo.h.

Next, in the code where I want to do the backtrace I have copied the function from the example:

//trying to include the c backtrace capability
#include <execinfo.h>

void show_stackframe() {
void *trace[16];
char **messages = (char **)NULL;
int i, trace_size = 0;

trace_size = backtrace(trace, 16);
messages = backtrace_symbols(trace, trace_size);
printk(KERN_ERR "[bt] Execution path:\n");
for (i=0; i<trace_size; ++i)
    printk(KERN_ERR "[bt] %s\n", messages[i]);
}
//backtrace function

I have put the call to this function later on, in a block driver function where the first sign of the error happens. Simply:

show_stackframe();

So when I compile it, the following errors:

user@slinux:~/2.6-32$ make -s
Invoking make againt the kernel at /lib/modules/2.6.32-5-686/build
In file included from /usr/include/features.h:346,
        from /usr/include/execinfo.h:22,
        from /home/linux/2.6-32/block/block26.c:49:
/usr/include/sys/cdefs.h:287:1: warning: "__always_inline" redefined
In file included from /usr/src/linux-headers-2.6.32-5-common/include/linux/compiler-gcc.h:86,
        from /usr/src/linux-headers-2.6.32-5-common/include/linux/compiler.h:40,
        from /usr/src/linux-headers-2.6.32-5-common/include/linux/stddef.h:4,
        from /usr/src/linux-headers-2.6.32-5-common/include/linux/list.h:4,
        from /usr/src/linux-headers-2.6.32-5-common/include/linux/module.h:9,
        from /home/linux/2.6-32/inc/linux_ver.h:40,
        from /home/linux/2.6-32/block/block26.c:32:
/usr/src/linux-headers-2.6.32-5-common/include/linux/compiler-gcc4.h:15:1: warning: this is the location of the previous definition
    /home/linux/2.6-32/block/block26.c:50: warning: function declaration isn’t a prototype
WARNING: "backtrace" [/home/linux/2.6-32/ndas_block.ko] undefined!
WARNING: "backtrace_symbols" [/home/linux/2.6-32/ndas_block.ko] undefined!

Note: block26.c is the file I am hoping to get the backtrace from.

Is there an obvious reason why the backtrace and backtrace_symbols remain undefined when it is compiled into the .ko modules?

I am guessing it because I use the compiler include execinfo.h which is residing on the computer and not being loaded to the module.

It is my uneducated guess to say the least.

Can anyone offer a help to get the backtrace functions loading up in the module?

Thanks for looking at this inquiry.

I am working on debian. When I take out the function and such, the module compiles fine and almost works perfectly.

From ndasusers

Answer 1

To print the stack contents and a backtrace to the kernel log, use the dump_stack() function in your kernel module. It's declared in linux/kernel.h in the include folder in the kernel source directory.