Debugging Linux kernel using kretprobes - Getting Function Return Value

-
Consider the scenario, where you want to find out the return value of a particular kernel function without modifying the kernel, kretprobes is the mechanism to go.

What are kretprobes?

 kretprobes allows you to call a user-defined function when the function returns.

Sample Code which will give the return value of fork() system call:

 #include <linux/kernel.h>
#include <linux/module.h>
#include <linux/kprobes.h>

MODULE_LICENSE("GPL");
static struct kretprobe retprobe;

static int ret_handler(struct kretprobe_instance *ri, struct pt_regs *regs)
{
    int retval = regs_return_value(regs);
    printk(KERN_INFO "%s returned %d\n", "_do_fork", retval);
    return 0;
}

static int test_kretprobe_init(void)
{
    int retval = 0;
    printk(KERN_INFO"%s: In init\n", __func__);
    retprobe.kp.symbol_name = "_do_fork";
    retprobe.handler = ret_handler;
    retval = register_kretprobe(&retprobe);
    if (retval < 0) {
        printk(KERN_INFO"register_kretprobe failed, returned:%d\n",
                retval);
    }
    return retval;
}

static void test_kretprobe_exit(void)
{
    unregister_kretprobe(&retprobe);
    printk(KERN_INFO"%s: In exit\n", __func__);
}
module_init(test_kretprobe_init);

module_exit(test_kretprobe_exit);

Output:


Comments

Post a Comment

Popular posts from this blog

bb.utils.contains yocto

-
Image
bb.utils.contains  is most commonly used function in Yocto. grep in poky directory returned with 696 count. $ grep -nr 'bb.utils.contains' poky/ | wc -l 696 It's definition is present in 'poky/bitbake/lib/bb/utils.py' file This function returns third argument if the second argument is subset of the first argument else returns fourth argument Let's take an example to understand this. You can see from the above screenshot, when the second argument is a subset of first argument, "present" was returned, else "notpresent" was returned We can also use bb.utils.contains inside if loop. This we can use inside a recipe. if ${@bb.utils.contains('SOMEFLAG','NEWVALUE3','true','false',d)}; then     FOO = 'HELLO' fi
Read more

Difference between RDEPENDS and DEPENDS in Yocto

-
We normally observe these two (RDEPENDS and DEPENDS) whenever we open any recipe. What should we choose when we write our own recipe. DEPENDS -> Build Time Dependency RDEPENDS -> Run Time Dependency DEPENDS: When a recipe 'A' is DEPENDS on recipe 'B'. In this case, Bitbake first builds recipe 'B' and then recipe 'A' E.g. You need 'dbus' to be built before 'wpa_supplicant'. RDEPENDS: When a recipe 'A' is RDEPENDS on recipe 'B'. In this case, Bitbake deploys 'B' on the target system when it deploys 'A'.  E.g. 'perf' RDEPENDS on 'bash' In other words, DEPENDS are those set of packages that should be available while building package, whereas RDEPENDS are set of packages that should be available during execution of the program.
Read more

PR, PN and PV Variable in Yocto

-
PN : Represents the name of the recipe. The name is usually extracted from the recipe file name. PR:  Represents the revision of the recipe. Default value for this revision is "r0". Subsequent revisions of the recipe conventionally will have "r1", "r2" and so on. PV:  Represents the version of the recipe. Normally extracted from the recipe file name. For example: ffmpeg_3.4.2.bb recipe. ${PN} : ffmpeg ${PV} : 3.4.2
Read more