Fix recursive anon structures in btf. 8000 #187
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Pull Request Overview
This PR addresses the recursive handling of anonymous structures in BTF definitions by updating offset calculation routines and cleaning up kprobe structure definitions.
- kprobe_defs.h: Updated the string identifiers to remove the redundant "(anon)" reference.
- btf.c: Introduced a recursive helper function (btf_offsetof_rec) for offset computation and updated related functions accordingly.
Reviewed Changes
Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.
| File | Description |
|---|---|
| kprobe_defs.h | Edited probe parameter labels to remove "(anon)" from the path. |
| btf.c | Refactored offset computation functions to support recursion and adjusted anonymous structure handling. |
Comments suppressed due to low confidence (1)
btf.c:214
- The btf_root_offset2 function no longer checks that the offset is a multiple of 8 and does not perform a division by 8. Please confirm that this change in behavior is intentional and consistent with the expected offset units.
return (off);
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nfritts
approved these changes
Jun 9, 2025
nicholasberlin
approved these changes
Jun 9, 2025
Consider the following structure:
```
struct iov_iter {
u8 iter_type;
bool copy_mc;
bool nofault;
bool data_source;
bool user_backed;
union {
size_t iov_offset;
int last_offset;
};
union {
struct iovec __ubuf_iovec;
struct {
union {
/* use iter_iov() to get the current vec */
----------> const struct iovec *__iov;
const struct kvec *kvec;
const struct bio_vec *bvec;
struct xarray *xarray;
void __user *ubuf;
};
size_t count;
};
};
union {
unsigned long nr_segs;
loff_t xarray_start;
};
};
```
If we want to get the offsetof(iov_iter, __iov) we need to go through 3
anonymous structures/unions.
This change makes it so that when we ask for iov_iter.__iov and we encounter an
anonymous structure/union in its members, we recurse into it trying to find
___iov.
Fixes tty_probes that rely on iov_iter.__iov, as a bonus it cuts the (anon) hack
we had before, now we don't need to specify anything, which implies a btfhub.c
regen in the upcoming commits.
Spotted, debugged and verified that the fix works by @nicholasberlin, many
thanks!!!
Co-authored-by: Nicholas Berlin <56366649+nicholasberlin@users.noreply.github.com>
In libbf commit 62e8af46d2c269300f1e9e019ef717b283bd808a, the default error scheme has changed to libbpf_set_strict_mode(), which means no more error codes embeded in pointers. The commit is from 2022, and quark started in 2024, so it never made sense to use IS_ERR_OF_NULL, as it would always be NULL. Makes the code a bit more digestible and cuts an ugly include.
Now that the btf parser is recursive for anonymous structures, we don't need this anymore, see previous commit.
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Fix recursive anon structures in btf
Consider the following structure:
If we want to get the offsetof(iov_iter, __iov) we need to go through 3
anonymous structures/unions.
This change makes it so that when we ask for iov_iter.__iov and we encounter an
anonymous structure/union in its members, we recurse into it trying to find
___iov.
Fixes tty_probes that rely on iov_iter.__iov, as a bonus it cuts the (anon) hack
we had before, now we don't need to specify anything, which implies a btfhub.c
regen in the upcoming commits.
Spotted, debugged and verified that the fix works by @nicholasberlin, many
thanks!!!
+++
Adapt libbpf error handling to post 1.0
In libbf commit 62e8af46d2c269300f1e9e019ef717b283bd808a, the default error
scheme has changed to libbpf_set_strict_mode(), which means no more error codes
embeded in pointers. The commit is from 2022, and quark started in 2024, so it
never made sense to use IS_ERR_OF_NULL, as it would always be NULL.
Makes the code a bit more digestible and cuts an ugly include.