Hi all,
Feature request:
To support checking the type of a specific field directly.
Background:
Currently, As far as I know, CORE is able to check a field’s
existence, offset, size and signedness, but not the field’s type
directly.
There are changes that convert a field from a scalar type to a struct
type, without changing the field’s name, offset or size. In that case,
it is currently difficult to use CORE to check such changes. For a
concrete example,
Commit 94a9717b3c (“locking/rwsem: Make rwsem->owner an atomic_long_t”)
Changed the type of rw_semaphore::owner from tast_struct * to
atomic_long_t. In that change, the field name, offset and size remain
the same. But the BPF program code used to extract the value is
different. For the kernel where the field is a pointer, we can write:
sem->owner
While in the kernel where the field is an atomic, we need to write:
sem->owner.counter.
It would be great to be able to check a field’s type directly.
Probably something like:
#include “vmlinux.h”
struct rw_semaphore__old {
struct task_struct *owner;
};
struct rw_semaphore__new {
atomic_long_t owner;
};
u64 owner;
if (bpf_core_field_type_is(sem->owner, struct task_struct *)) {
struct rw_semaphore__old *old = (struct rw_semaphore__old *)sem;
owner = (u64)sem->owner;
} else if (bpf_core_field_type_is(sem->owner, atomic_long_t)) {
struct rw_semaphore__new *new = (struct rw_semaphore__new *)sem;
owner = new->owner.counter;
}
Hao
