Em Mon, Oct 23, 2023 at 10:57:21AM +0100, Alan Maguire escreveu:
> Currently, the kernel uses pahole version checking as the way to
> determine which BTF encoding features to request from pahole. This
> means that such features have to be tied to a specific version and
> as new features are added, additional clauses in scripts/pahole-flags.sh
> have to be added; for example
Finally trying to test this:
I started with a random vmlinux file, already with BTF:
$ bpftool btf dump file vmlinux.v5.19.0-rc5+ format raw > vmlinux.v5.19.0-rc5+.dump.original
$ wc -l vmlinux.v5.19.0-rc5+.dump.original
291961 vmlinux.v5.19.0-rc5+.dump.original
$ grep -i enum64 vmlinux.v5.19.0-rc5+.dump.original | wc -l
0
$
$ grep -i enum vmlinux.v5.19.0-rc5+.dump.original | wc -l
2175
$
Ok, now I want to encode just with enum64, i.e. all the other features
will not be enabled via this new option and only the enum64 will, if
present in the DWARF info:
$ cp vmlinux.v5.19.0-rc5+ vmlinux.v5.19.0-rc5+.enum64 ; pahole --btf_encode --btf_features=enum64 vmlinux.v5.19.0-rc5+.enum64
$
I tried using --btf_encode_detached=file but then couldn't find a way to
make 'bpftool btf' to consume detached BTF, it seems that "file" means
"ELF file containing BTF" so I copied the original file to then reencode
BTF selecting just the enum64 feature, the resulting file continues to
have the original DWARF and the BTF using that --btf_features set:
[acme@quaco pahole]$ pahole -F btf vmlinux.v5.19.0-rc5+.enum64 | wc -l
143161
[acme@quaco pahole]$ pahole -F dwarf vmlinux.v5.19.0-rc5+.enum64 | wc -l
143589
[acme@quaco pahole]$
[acme@quaco pahole]$ pahole --expand_types -F btf vmlinux.v5.19.0-rc5+.enum64 -C spinlock
struct spinlock {
union {
struct raw_spinlock {
/* typedef arch_spinlock_t */ struct qspinlock {
union {
/* typedef atomic_t */ struct {
int counter; /* 0 4 */
} val; /* 0 4 */
struct {
/* typedef u8 -> __u8 */ unsigned char locked; /* 0 1 */
/* typedef u8 -> __u8 */ unsigned char pending; /* 1 1 */
}; /* 0 2 */
struct {
/* typedef u16 -> __u16 */ short unsigned int locked_pending; /* 0 2 */
/* typedef u16 -> __u16 */ short unsigned int tail; /* 2 2 */
}; /* 0 4 */
}; /* 0 4 */
} raw_lock; /* 0 4 */
}rlock; /* 0 4 */
}; /* 0 4 */
/* size: 4, cachelines: 1, members: 1 */
/* last cacheline: 4 bytes */
};
[acme@quaco pahole]$
But 'bpftool bpf' doesn't like it:
$ bpftool btf dump file vmlinux.v5.19.0-rc5+.enum64 raw
Error: failed to load BTF from vmlinux.v5.19.0-rc5+.enum64: Invalid argument
$
But it doesn't like it even when not using --btf_features :-\
$ cp vmlinux.v5.19.0-rc5+ vmlinux.v5.19.0-rc5+.default_btf_encode ; pahole --btf_encode vmlinux.v5.19.0-rc5+.default_btf_encode
$ bpftool btf dump file vmlinux.v5.19.0-rc5+.default_btf_encode raw | wc -l
Error: failed to load BTF from vmlinux.v5.19.0-rc5+.default_btf_encode: Invalid argument
0
$
I'll try to root cause this problem...
- Arnaldo
