Why does bpftrace treat char pointer as integer?

Question

I run the bpftrace command as below:

bpftrace -e 'kprobe:f2fs_file_write_iter { printf("process:%s  file:%s  inode:%ld offset:%ld count:%ld\n", comm, (((struct kiocb *)arg0)->ki_filp->f_path.dentry->d_name.name),  ((struct kiocb *)arg0)->ki_filp->f_inode->i_ino, ((struct kiocb *)arg0)->ki_pos, ((struct iov_iter *)arg1)->count ); }'

But it reports the following error:

stdin:1:31-284: ERROR: printf: %s specifier expects a value of type string (integer supplied)

From linux kernel source code, we can know that ((struct kiocb *)arg0)->ki_filp->f_path.dentry->d_name.name is of type char pointer. But why does bpftrace treat it as integer?

I tried to force type conversion, but it reported another error as below:

root@localhost:/usr/share/bcc/tools#  bpftrace -e 'kprobe:f2fs_file_write_iter { printf("process:%s  file:%s  inode:%ld offset:%ld count:%ld\n", comm, (char *)(((struct kiocb *)arg0)->ki_filp->f_path.dentry->d_name.name),  ((struct kiocb *)arg0)->ki_filp->f_inode->i_ino, ((struct kiocb *)arg0)->ki_pos, ((struct iov_iter *)arg1)->count ); }'
stdin:1:107-109: ERROR: syntax error, unexpected )
kprobe:f2fs_file_write_iter { printf("process:%s  file:%s  inode:%ld offset:%ld count:%ld\n", comm, (char *)(((struct kiocb *)arg0)->ki_filp->f_path.dentry->d_name.name),  ((struct kiocb *)arg0)->ki_filp->f_inode->i_ino, ((struct kiocb *)arg0)->ki_pos, ((struct iov_iter *)arg1)->count ); }

How to fix it?

Answer 1

I find a way to fix it: converting type by str().

I replace ((struct kiocb *)arg0)->ki_filp->f_path.dentry->d_name.name with str(((struct kiocb *)arg0)->ki_filp->f_path.dentry->d_name.name). It works.