Em Thu, Oct 08, 2020 at 04:39:53PM -0700, Andrii Nakryiko escreveu:
> From: Andrii Nakryiko <andriin@xxxxxx>
>
> Switch BTF loading to completely use libbpf's own struct btf and related APIs.
> BTF encoding is still happening with pahole's own code, so these two code
> paths are not sharing anything now. String fetching is happening based on
> whether btfe->strings were set to non-NULL pointer by btf_encoder.
While testing this one I noticed a problem, but it isn't caused by this
particular patch:
[acme@five pahole]$ cp ~/git/build/v5.9-rc6+/net/ipv4/tcp_ipv4.o .
[acme@five pahole]$ readelf -SW tcp_ipv4.o | grep BTF
[acme@five pahole]$ pahole -J tcp_ipv4.o
[acme@five pahole]$ readelf -SW tcp_ipv4.o | grep BTF
[105] .BTF PROGBITS 0000000000000000 0fbb3c 03f697 00 0 0 1
[acme@five pahole]$ ./btfdiff tcp_ipv4.o
--- /tmp/btfdiff.dwarf.BDAvGi 2020-10-09 11:41:45.161509391 -0300
+++ /tmp/btfdiff.btf.p81icw 2020-10-09 11:41:45.177509720 -0300
@@ -4056,7 +4056,7 @@ struct tcp_congestion_ops {
u32 (*min_tso_segs)(struct sock *); /* 96 8 */
u32 (*sndbuf_expand)(struct sock *); /* 104 8 */
void (*cong_control)(struct sock *, const struct rate_sample *); /* 112 8 */
- size_t (*get_info)(struct sock *, u32, int *, union tcp_cc_info *); /* 120 8 */
+ size_t (*get_info)(struct sock *, u32, int *, struct tcp_cc_info *); /* 120 8 */
/* --- cacheline 2 boundary (128 bytes) --- */
char name[16]; /* 128 16 */
struct module * owner; /* 144 8 */
[acme@five pahole]$ git log --oneline -5
ef4f971a9cf745fc (HEAD) dwarf_loader: Conditionally define DW_AT_alignment
cc3f9dce3378280f pahole: Implement --packed
08f49262f474370a man-pages: Fix 'coimbine' typo
fdc639188cb514e4 (tag: v1.18) dwarves: Prep v1.18
70c3e669709b6351 spec: Set the build type to 'Release'
[acme@five pahole]$
And looking at the source code it is a union:
include/net/tcp.h
size_t (*get_info)(struct sock *sk, u32 ext, int *attr,
union tcp_cc_info *info);
So this tcp_cc_info isn't available in DWARF and thus isn't available in
the resulting BTF:
[acme@five pahole]$ pahole -F dwarf -C tcp_cc_info tcp_ipv4.o
pahole: type 'tcp_cc_info' not found
[acme@five pahole]$ pahole -F btf -C tcp_cc_info tcp_ipv4.o
pahole: type 'tcp_cc_info' not found
[acme@five pahole]$
If you look at /sys/kernel/btf/vmlinux it is there:
[acme@five pahole]$ pahole tcp_cc_info
union tcp_cc_info {
struct tcpvegas_info vegas; /* 0 16 */
struct tcp_dctcp_info dctcp; /* 0 16 */
struct tcp_bbr_info bbr; /* 0 20 */
};
[acme@five pahole]$
I.e. when encoding vmlinux we're good and for the BTF use case so far
this is thus not a problem, will continue processing your patches and
then later try to figure this out.
For completeness when looking at tcp_congestion_ops using
/sys/kernel/btf/vmlinux, all is ok:
[acme@five pahole]$ pahole tcp_congestion_ops
struct tcp_congestion_ops {
struct list_head list; /* 0 16 */
u32 key; /* 16 4 */
u32 flags; /* 20 4 */
void (*init)(struct sock *); /* 24 8 */
void (*release)(struct sock *); /* 32 8 */
u32 (*ssthresh)(struct sock *); /* 40 8 */
void (*cong_avoid)(struct sock *, u32, u32); /* 48 8 */
void (*set_state)(struct sock *, u8); /* 56 8 */
/* --- cacheline 1 boundary (64 bytes) --- */
void (*cwnd_event)(struct sock *, enum tcp_ca_event); /* 64 8 */
void (*in_ack_event)(struct sock *, u32); /* 72 8 */
u32 (*undo_cwnd)(struct sock *); /* 80 8 */
void (*pkts_acked)(struct sock *, const struct ack_sample *); /* 88 8 */
u32 (*min_tso_segs)(struct sock *); /* 96 8 */
u32 (*sndbuf_expand)(struct sock *); /* 104 8 */
void (*cong_control)(struct sock *, const struct rate_sample *); /* 112 8 */
size_t (*get_info)(struct sock *, u32, int *, union tcp_cc_info *); /* 120 8 */
/* --- cacheline 2 boundary (128 bytes) --- */
char name[16]; /* 128 16 */
struct module * owner; /* 144 8 */
/* size: 152, cachelines: 3, members: 18 */
/* last cacheline: 24 bytes */
};
[acme@five pahole]$
And a btfdiff on vmlinux also shows BTF and DWARF produce the same
results:
[acme@five pahole]$ cp ~/git/build/bpf-next-v5.9.0-rc8+/vmlinux .
[acme@five pahole]$ readelf -SW vmlinux | grep BTF
[24] .BTF PROGBITS ffffffff82494ac0 1694ac0 340207 00 A 0 0 1
[25] .BTF_ids PROGBITS ffffffff827d4cc8 19d4cc8 0000a4 00 A 0 0 1
[acme@five pahole]$ ./btfdiff vmlinux
[acme@five pahole]$
- Arnaldo
