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Message-Id: <20240123204437.1322700-1-irogers@google.com>
Date: Tue, 23 Jan 2024 12:44:37 -0800
From: Ian Rogers <irogers@...gle.com>
To: Alan Maguire <alan.maguire@...cle.com>, Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>, Andrii Nakryiko <andrii@...nel.org>,
Martin KaFai Lau <martin.lau@...ux.dev>, Song Liu <song@...nel.org>,
Yonghong Song <yonghong.song@...ux.dev>, John Fastabend <john.fastabend@...il.com>,
KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...gle.com>, Hao Luo <haoluo@...gle.com>,
Jiri Olsa <jolsa@...nel.org>, bpf@...r.kernel.org, linux-kernel@...r.kernel.org
Cc: Ian Rogers <irogers@...gle.com>
Subject: [PATCH v2] libbpf: Add some details for BTF parsing failures
As CONFIG_DEBUG_INFO_BTF is default off the existing "failed to find
valid kernel BTF" message makes diagnosing the kernel build issue some
what cryptic. Add a little more detail with the hope of helping users.
Before:
```
libbpf: failed to find valid kernel BTF
libbpf: Error loading vmlinux BTF: -3
libbpf: failed to load object 'lock_contention_bpf'
libbpf: failed to load BPF skeleton 'lock_contention_bpf': -3
```
After no access /sys/kernel/btf/vmlinux:
```
libbpf: Unable to access canonical vmlinux BTF from /sys/kernel/btf/vmlinux
libbpf: Error loading vmlinux BTF: -3
libbpf: failed to load object 'lock_contention_bpf'
libbpf: failed to load BPF skeleton 'lock_contention_bpf': -3
```
After no BTF /sys/kernel/btf/vmlinux:
```
libbpf: Failed to load vmlinux BTF from /sys/kernel/btf/vmlinux, was CONFIG_DEBUG_INFO_BTF enabled?
libbpf: Error loading vmlinux BTF: -3
libbpf: failed to load object 'lock_contention_bpf'
libbpf: failed to load BPF skeleton 'lock_contention_bpf': -3
```
Closes: https://lore.kernel.org/bpf/CAP-5=fU+DN_+Y=Y4gtELUsJxKNDDCOvJzPHvjUVaUoeFAzNnig@mail.gmail.com/
Signed-off-by: Ian Rogers <irogers@...gle.com>
---
v2. Try to address review comments from Andrii Nakryiko.
---
tools/lib/bpf/btf.c | 49 ++++++++++++++++++++++++++++++++-------------
1 file changed, 35 insertions(+), 14 deletions(-)
diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c
index ee95fd379d4d..d8a05dda0836 100644
--- a/tools/lib/bpf/btf.c
+++ b/tools/lib/bpf/btf.c
@@ -4920,16 +4920,25 @@ static int btf_dedup_remap_types(struct btf_dedup *d)
return 0;
}
+static struct btf *btf__load_vmlinux_btf_path(const char *path)
+{
+ struct btf *btf;
+ int err;
+
+ btf = btf__parse(path, NULL);
+ err = libbpf_get_error(btf);
+ pr_debug("loading kernel BTF '%s': %d\n", path, err);
+ return err ? NULL : btf;
+}
+
/*
* Probe few well-known locations for vmlinux kernel image and try to load BTF
* data out of it to use for target BTF.
*/
struct btf *btf__load_vmlinux_btf(void)
{
+ /* fall back locations, trying to find vmlinux on disk */
const char *locations[] = {
- /* try canonical vmlinux BTF through sysfs first */
- "/sys/kernel/btf/vmlinux",
- /* fall back to trying to find vmlinux on disk otherwise */
"/boot/vmlinux-%1$s",
"/lib/modules/%1$s/vmlinux-%1$s",
"/lib/modules/%1$s/build/vmlinux",
@@ -4938,29 +4947,41 @@ struct btf *btf__load_vmlinux_btf(void)
"/usr/lib/debug/boot/vmlinux-%1$s.debug",
"/usr/lib/debug/lib/modules/%1$s/vmlinux",
};
- char path[PATH_MAX + 1];
+ const char *location;
struct utsname buf;
struct btf *btf;
- int i, err;
+ int i;
- uname(&buf);
+ /* try canonical vmlinux BTF through sysfs first */
+ location = "/sys/kernel/btf/vmlinux";
+ if (faccessat(AT_FDCWD, location, R_OK, AT_EACCESS) == 0) {
+ btf = btf__load_vmlinux_btf_path(location);
+ if (btf)
+ return btf;
+
+ pr_warn("Failed to load vmlinux BTF from %s, was CONFIG_DEBUG_INFO_BTF enabled?\n",
+ location);
+ } else
+ pr_warn("Unable to access canonical vmlinux BTF from %s\n", location);
+ uname(&buf);
for (i = 0; i < ARRAY_SIZE(locations); i++) {
- snprintf(path, PATH_MAX, locations[i], buf.release);
+ char path[PATH_MAX + 1];
+
+ snprintf(path, sizeof(path), locations[i], buf.release);
+ btf = btf__load_vmlinux_btf_path(path);
if (faccessat(AT_FDCWD, path, R_OK, AT_EACCESS))
continue;
- btf = btf__parse(path, NULL);
- err = libbpf_get_error(btf);
- pr_debug("loading kernel BTF '%s': %d\n", path, err);
- if (err)
- continue;
+ btf = btf__load_vmlinux_btf_path(location);
+ if (btf)
+ return btf;
- return btf;
+ pr_warn("Failed to load vmlinux BTF from %s, was CONFIG_DEBUG_INFO_BTF enabled?\n",
+ path);
}
- pr_warn("failed to find valid kernel BTF\n");
return libbpf_err_ptr(-ESRCH);
}
--
2.43.0.429.g432eaa2c6b-goog
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