systemtap failed to probe the functions. Registration error - linux-kernel

Question

systemtap registration error.
WARNING: probe process("/home/user/a.out").function("func").return inode-offset 00000000468ed0c6 registration error (rc -5)
WARNING: probe process("/home/user/a.out").function("func").call inode-offset 00000000468ed0c6 registration error (rc -5)
WARNING: task_finder mmap inode-uprobes callback for task 28532 failed: -5
I am learning systemtap. I have a process which calls a function in a while loop. When I start systemtap using "stap -v test.stp" to probe the userspace function, I get the registration error. Following is the complete screen shot;
Pass 1: parsed user script and 465 library scripts using 112640virt/48788res/6452shr/42636data kb, in 100usr/20sys/123real ms.
Pass 2: analyzed script: 3 probes, 2 functions, 4 embeds, 3 globals using 114256virt/51968res/7840shr/44252data kb, in 50usr/110sys/162real ms.
Pass 3: using cached /root/.systemtap/cache/66/stap_662fe7689c5fb5d6ef569e8246fa1c8a_3296.c
Pass 4: using cached /root/.systemtap/cache/66/stap_662fe7689c5fb5d6ef569e8246fa1c8a_3296.ko
Pass 5: starting run.
WARNING: probe process("/home/admin/a.out").function("func").return inode-offset 00000000468ed0c6 registration error (rc 0)
WARNING: probe process("/home/admin/a.out").function("func").call inode-offset 00000000468ed0c6 registration error (rc 0)
^CERROR: empty aggregate near operator '#max' at test.stp:6:37
WARNING: Number of errors: 1, skipped probes: 0
WARNING: /usr/bin/staprun exited with status: 1
Pass 5: run completed in 0usr/20sys/9318real ms.
Pass 5: run failed. [man error::pass5]
test.stp
probe process("/home/user/a.out").function("func").return {
stats <<< gettimeofday_ns() - #entry(gettimeofday_ns())
}
probe end {
printf("max/avg/min: %d/%d/%d\n", #max(stats), #avg(stats), #min(stats))
print(#hist_log(stats))
}
global stats
test.c
#include <stdlib.h>
#include <unistd.h>
void func()
{
printf("Hello\n");
sleep(1);
}
int main()
{
while (1)
{
func();
}
}

Answer 1

systemtap does not support overlays/union filesystems. The systemtap userspace code has to be changed to get the real inode of a file if it is in overlayfs. For this the systemtap need to be code changed and built. Download systemtap source code make changes in the file uprobes-inode.c . The change is to use the d_backing_inode to find inode. Need to make changes in two places.
inode_1 = d_backing_inode(d_real((struct dentry *) dentry, NULL, 0, 0)); //use inode_1 in the following function.
if ((vm_flags & VM_EXEC) && !(vm_flags & VM_WRITE))
rc = stapiu_change_plus(target, task, addr, length,
offset, vm_flags, inode_1);
// offset, vm_flags, dentry->d_inode);
vm_file = stap_find_exe_file(mm);
if (vm_file) {
if (vm_file->f_path.dentry)
{
//inode = vm_file->f_path.dentry->d_inode;
inode = d_backing_inode(d_real((struct dentry *) vm_file->f_path.dentry, NULL, 0, 0));
}
fput(vm_file);