On 2/7/24 10:51 AM, Bryce Kahle wrote:
On Mon, Feb 5, 2024 at 10:21 AM Andrii Nakryiko
<andrii.nakryiko@xxxxxxxxx> wrote:
3) btf__dedup() will deduplicate everything, so that only unique type
definitions remain.
A random thought about another way.
At module side, we keep
- module btf
- another section (e.g. .BTF.extra) to keep minimum kernel-side
types which directly used by module btf
for example, module btf has
struct foo {
struct task_struct *t;
}
module btf encoding will have id, say 20,
for 'struct task_struct' which is at that time
the id in linux kernel.
Then the module .BTF.extra contains
id 20: struct task_struct type encoding
there is no need to encode more types beyond pointers.
this can be simpler or more complex depending
on what to do during module load.
When a module load:
For each .BTF.extra entry, trying to match
the corresponding types in the current kernel.
The type in the current type should have same
size as the one in .BTF.extra if otherwise
layout in the module btf may change.
If new kernel type can be used for module BTF,
simply replace the old id with new id in module BTF.
Otherwise, type mismatch may happen and the corresponding
module btf type should be invalidated.
Since minimization only keeps used struct and union members, couldn't
you have two internal types from different modules which conflict and
end up using the wrong offset?
Example:
in module M:
struct S {
... // other unused members
int x; // offset 12 (for example)
}
in module N:
struct S {
... // other unused members
int x; // offset 20 (something different from S.x in module M)
}
