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Message-Id: <1643645554-28723-3-git-send-email-alan.maguire@oracle.com>
Date: Mon, 31 Jan 2022 16:12:32 +0000
From: Alan Maguire <alan.maguire@...cle.com>
To: andrii@...nel.org, ast@...nel.org, daniel@...earbox.net
Cc: kafai@...com, songliubraving@...com, yhs@...com,
john.fastabend@...il.com, kpsingh@...nel.org, jolsa@...nel.org,
sunyucong@...il.com, netdev@...r.kernel.org, bpf@...r.kernel.org,
Alan Maguire <alan.maguire@...cle.com>
Subject: [PATCH v3 bpf-next 2/4] libbpf: add auto-attach for uprobes based on section name
Now that u[ret]probes can use name-based specification, it makes
sense to add support for auto-attach based on SEC() definition.
The format proposed is
SEC("u[ret]probe//path/to/prog:[raw_offset|[function_name[+offset]]")
For example, to trace malloc() in libc:
SEC("uprobe//usr/lib64/libc.so.6:malloc")
Auto-attach is done for all tasks (pid -1).
Note that there is a backwards-compatibility issue here. Consider a BPF
object consisting of a set of BPF programs, including a uprobe program.
Because uprobes did not previously support auto-attach, it's possible that
because the uprobe section name is not in auto-attachable form, overall
BPF skeleton attach would now fail due to the failure of the uprobe program
to auto-attach. So we need to handle the case of auto-attach failure where
the form of the section name is not suitable for auto-attach without
a complete attach failure. On surveying the code, bpf_program__attach()
already returns -ESRCH in cases where no auto-attach function is
supplied, so for consistency with that - and because that return value
is less likely to collide with actual attach failures than -EOPNOTSUPP -
it is used as the attach function return value signalling auto-attach
is not possible.
Signed-off-by: Alan Maguire <alan.maguire@...cle.com>
---
tools/lib/bpf/libbpf.c | 77 ++++++++++++++++++++++++++++++++++++++++++++++++--
1 file changed, 74 insertions(+), 3 deletions(-)
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index eb95629..e2b4415 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -8581,6 +8581,7 @@ int bpf_program__set_log_buf(struct bpf_program *prog, char *log_buf, size_t log
}
static struct bpf_link *attach_kprobe(const struct bpf_program *prog, long cookie);
+static struct bpf_link *attach_uprobe(const struct bpf_program *prog, long cookie);
static struct bpf_link *attach_tp(const struct bpf_program *prog, long cookie);
static struct bpf_link *attach_raw_tp(const struct bpf_program *prog, long cookie);
static struct bpf_link *attach_trace(const struct bpf_program *prog, long cookie);
@@ -8592,9 +8593,9 @@ int bpf_program__set_log_buf(struct bpf_program *prog, char *log_buf, size_t log
SEC_DEF("sk_reuseport/migrate", SK_REUSEPORT, BPF_SK_REUSEPORT_SELECT_OR_MIGRATE, SEC_ATTACHABLE | SEC_SLOPPY_PFX),
SEC_DEF("sk_reuseport", SK_REUSEPORT, BPF_SK_REUSEPORT_SELECT, SEC_ATTACHABLE | SEC_SLOPPY_PFX),
SEC_DEF("kprobe/", KPROBE, 0, SEC_NONE, attach_kprobe),
- SEC_DEF("uprobe/", KPROBE, 0, SEC_NONE),
+ SEC_DEF("uprobe/", KPROBE, 0, SEC_NONE, attach_uprobe),
SEC_DEF("kretprobe/", KPROBE, 0, SEC_NONE, attach_kprobe),
- SEC_DEF("uretprobe/", KPROBE, 0, SEC_NONE),
+ SEC_DEF("uretprobe/", KPROBE, 0, SEC_NONE, attach_uprobe),
SEC_DEF("tc", SCHED_CLS, 0, SEC_NONE),
SEC_DEF("classifier", SCHED_CLS, 0, SEC_NONE | SEC_SLOPPY_PFX),
SEC_DEF("action", SCHED_ACT, 0, SEC_NONE | SEC_SLOPPY_PFX),
@@ -10525,6 +10526,64 @@ static long elf_find_func_offset(const char *binary_path, const char *name)
}
+/* Format of u[ret]probe section definition supporting auto-attach:
+ * u[ret]probe//path/to/prog:function[+offset]
+ *
+ * Many uprobe programs do not avail of auto-attach, so we need to handle the
+ * case where the format is uprobe/myfunc by returning NULL rather than an
+ * error.
+ */
+static struct bpf_link *attach_uprobe(const struct bpf_program *prog, long cookie)
+{
+ DECLARE_LIBBPF_OPTS(bpf_uprobe_opts, opts);
+ char *func_name, binary_path[512];
+ unsigned int raw_offset;
+ char *func, *probe_name;
+ struct bpf_link *link;
+ size_t offset = 0;
+ int n, err;
+
+ opts.retprobe = str_has_pfx(prog->sec_name, "uretprobe/");
+ if (opts.retprobe)
+ probe_name = prog->sec_name + sizeof("uretprobe/") - 1;
+ else
+ probe_name = prog->sec_name + sizeof("uprobe/") - 1;
+
+ snprintf(binary_path, sizeof(binary_path), "%s", probe_name);
+ /* ':' should be prior to function+offset */
+ func_name = strrchr(binary_path, ':');
+ if (!func_name) {
+ pr_debug("section '%s' is old-style u[ret]probe/function, cannot auto-attach\n",
+ prog->sec_name);
+ return libbpf_err_ptr(-ESRCH);
+ }
+ func_name[0] = '\0';
+ func_name++;
+ n = sscanf(func_name, "%m[a-zA-Z0-9_.]+%li", &func, &offset);
+ if (n < 1) {
+ err = -EINVAL;
+ pr_warn("uprobe name is invalid: %s\n", func_name);
+ return libbpf_err_ptr(err);
+ }
+ /* Is func a raw address? */
+ if (n == 1 && sscanf(func, "%x", &raw_offset) == 1) {
+ free(func);
+ func = NULL;
+ offset = (size_t)raw_offset;
+ }
+ if (opts.retprobe && offset != 0) {
+ free(func);
+ err = -EINVAL;
+ pr_warn("uretprobes do not support offset specification\n");
+ return libbpf_err_ptr(err);
+ }
+ opts.func_name = func;
+
+ link = bpf_program__attach_uprobe_opts(prog, -1, binary_path, offset, &opts);
+ free(func);
+ return link;
+}
+
struct bpf_link *bpf_program__attach_uprobe(const struct bpf_program *prog,
bool retprobe, pid_t pid,
const char *binary_path,
@@ -12041,7 +12100,19 @@ int bpf_object__attach_skeleton(struct bpf_object_skeleton *s)
*link = bpf_program__attach(prog);
err = libbpf_get_error(*link);
- if (err) {
+ switch (err) {
+ case 0:
+ break;
+ case -ESRCH:
+ /* -ESRCH is used as it is less likely to collide with other error
+ * cases in program attach while being consistent with the value
+ * returned by bpf_program__attach() where no auto-attach function
+ * is provided.
+ */
+ pr_warn("auto-attach not supported for program '%s'\n",
+ bpf_program__name(prog));
+ break;
+ default:
pr_warn("failed to auto-attach program '%s': %d\n",
bpf_program__name(prog), err);
return libbpf_err(err);
--
1.8.3.1
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