Re: [RFC PATCH] tracing/kprobe: Support $$args for function entry
From: Alan Maguire
Date: Fri Sep 24 2021 - 13:51:51 EST
On 23/09/2021 13:39, Masami Hiramatsu wrote:
Support $$args fetch arg for function entry. This uses
BTF for finding the function argument. Thus it depends
on CONFIG_BPF_SYSCALL.
/sys/kernel/tracing # echo 'p vfs_read $$args' >> kprobe_events
/sys/kernel/tracing # cat kprobe_events
p:kprobes/p_vfs_read_0 vfs_read file=$arg1:x64 buf=$arg2:x64 count=$arg3:u64 pos=$arg4:x64
Note that $$args must be used without argument name.
This looks great! Can I ask which tree you're building on
top of so I can play around with this a bit?
I also wonder if we could rework btf_show_name() to help
render full type info for the args? in kernel/bpf/btf.c:
/*
* Populate show->state.name with type name information.
* Format of type name is
*
* [.member_name = ] (type_name)
*/
The (type_name) part is what we'd want from here; no reason
we can't refactor that function to make the type name available
as a cast. It would rework the output to be something like
p:kprobes/p_vfs_read_0 vfs_read struct file *file=$arg1 , char *buf=$arg2 , size_t count=$arg3 , loff_t pos=$arg4
...if that's wanted of course (not sure what the constraints on format are here)? Thanks for pushing this along!
Alan
Signed-off-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
---
kernel/trace/trace_kprobe.c | 60 ++++++++++++++++++++++++-
kernel/trace/trace_probe.c | 105 +++++++++++++++++++++++++++++++++++++++++++
kernel/trace/trace_probe.h | 5 ++
3 files changed, 168 insertions(+), 2 deletions(-)
diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
index 3dd4fb719aa3..fe88ee8c8cd8 100644
--- a/kernel/trace/trace_kprobe.c
+++ b/kernel/trace/trace_kprobe.c
@@ -712,6 +712,58 @@ static int trace_kprobe_module_callback(struct notifier_block *nb,
return NOTIFY_DONE;
}
+#ifdef CONFIG_BPF_SYSCALL
+
+static int trace_kprobe_parse_btf_args(struct trace_kprobe *tk, int i,
+ const char *arg, unsigned int flags)
+{
+ struct trace_probe *tp = &tk->tp;
+ static struct btf *btf;
+ const struct btf_type *t;
+ const struct btf_param *args;
+ s32 id, nargs;
+ int ret;
+
+ if (!(flags & TPARG_FL_FENTRY))
+ return -EINVAL;
+ if (!tk->symbol)
+ return -EINVAL;
+
+ if (!btf)
+ btf = btf_parse_vmlinux();
+
+ id = btf_find_by_name_kind(btf, tk->symbol, BTF_KIND_FUNC);
+ if (id <= 0)
+ return -ENOENT;
+
+ /* Get BTF_KIND_FUNC type */
+ t = btf_type_by_id(btf, id);
+ if (!btf_type_is_func(t))
+ return -ENOENT;
+
+ /* The type of BTF_KIND_FUNC is BTF_KIND_FUNC_PROTO */
+ t = btf_type_by_id(btf, t->type);
+ if (!btf_type_is_func_proto(t))
+ return -ENOENT;
+
+ args = (const struct btf_param *)(t + 1);
+ nargs = btf_type_vlen(t);
+ for (i = 0; i < nargs; i++) {
+ ret = traceprobe_parse_btf_arg(tp, i, btf, &args[i]);
+ if (ret < 0)
+ break;
+ }
+
+ return ret;
+}
+#else
+static int trace_kprobe_parse_btf_args(struct trace_kprobe *tk, int i,
+ const char *arg, unsigned int flags)
+{
+ return -EOPNOTSUPP;
+}
+#endif
+
static struct notifier_block trace_kprobe_module_nb = {
.notifier_call = trace_kprobe_module_callback,
.priority = 1 /* Invoked after kprobe module callback */
@@ -733,12 +785,13 @@ static int __trace_kprobe_create(int argc, const char *argv[])
* $stack : fetch stack address
* $stackN : fetch Nth of stack (N:0-)
* $comm : fetch current task comm
+ * $$args : fetch parameters using BTF
* @ADDR : fetch memory at ADDR (ADDR should be in kernel)
* @SYM[+|-offs] : fetch memory at SYM +|- offs (SYM is a data symbol)
* %REG : fetch register REG
* Dereferencing memory fetch:
* +|-offs(ARG) : fetch memory at ARG +|- offs address.
- * Alias name of args:
+ * Alias name of args (except for $$args) :
* NAME=FETCHARG : set NAME as alias of FETCHARG.
* Type of args:
* FETCHARG:TYPE : use TYPE instead of unsigned long.
@@ -877,7 +930,10 @@ static int __trace_kprobe_create(int argc, const char *argv[])
/* parse arguments */
for (i = 0; i < argc && i < MAX_TRACE_ARGS; i++) {
trace_probe_log_set_index(i + 2);
- ret = traceprobe_parse_probe_arg(&tk->tp, i, argv[i], flags);
+ if (strcmp(argv[i], "$$args") == 0)
+ ret = trace_kprobe_parse_btf_args(tk, i, argv[i], flags);
+ else
+ ret = traceprobe_parse_probe_arg(&tk->tp, i, argv[i], flags);
if (ret)
goto error; /* This can be -ENOMEM */
}
diff --git a/kernel/trace/trace_probe.c b/kernel/trace/trace_probe.c
index 2fe104109525..bbac261b1688 100644
--- a/kernel/trace/trace_probe.c
+++ b/kernel/trace/trace_probe.c
@@ -765,6 +765,111 @@ static int traceprobe_conflict_field_name(const char *name,
return 0;
}
+#ifdef CONFIG_BPF_SYSCALL
+
+static u32 btf_type_int(const struct btf_type *t)
+{
+ return *(u32 *)(t + 1);
+}
+
+static const char *traceprobe_type_from_btf(struct btf *btf, s32 id)
+{
+ const struct btf_type *t;
+ u32 intdata;
+ s32 tid;
+
+ /* TODO: const char * could be converted as a string */
+ t = btf_type_skip_modifiers(btf, id, &tid);
+
+ switch (BTF_INFO_KIND(t->info)) {
+ case BTF_KIND_ENUM:
+ /* enum is "int", so convert to "s32" */
+ return "s32";
+ case BTF_KIND_PTR:
+ /* pointer will be converted to "x??" */
+ if (IS_ENABLED(CONFIG_64BIT))
+ return "x64";
+ else
+ return "x32";
+ case BTF_KIND_INT:
+ intdata = btf_type_int(t);
+ if (BTF_INT_ENCODING(intdata) & BTF_INT_SIGNED) {
+ switch (BTF_INT_BITS(intdata)) {
+ case 8:
+ return "s8";
+ case 16:
+ return "s16";
+ case 32:
+ return "s32";
+ case 64:
+ return "s64";
+ }
+ } else { /* unsigned */
+ switch (BTF_INT_BITS(intdata)) {
+ case 8:
+ return "u8";
+ case 16:
+ return "u16";
+ case 32:
+ return "u32";
+ case 64:
+ return "u64";
+ }
+ }
+ }
+
+ /* Default type */
+ if (IS_ENABLED(CONFIG_64BIT))
+ return "x64";
+ else
+ return "x32";
+}
+
+int traceprobe_parse_btf_arg(struct trace_probe *tp, int i, struct btf *btf,
+ const struct btf_param *arg)
+{
+ struct probe_arg *parg = &tp->args[i];
+ const char *name, *tname;
+ char *body;
+ int ret;
+
+ tp->nr_args++;
+ name = btf_name_by_offset(btf, arg->name_off);
+ parg->name = kstrdup(name, GFP_KERNEL);
+ if (!parg->name)
+ return -ENOMEM;
+
+ if (!is_good_name(parg->name)) {
+ trace_probe_log_err(0, BAD_ARG_NAME);
+ return -EINVAL;
+ }
+ if (traceprobe_conflict_field_name(parg->name, tp->args, i)) {
+ trace_probe_log_err(0, USED_ARG_NAME);
+ return -EINVAL;
+ }
+
+ /*
+ * Since probe event needs an appropriate command for dyn_event interface,
+ * convert BTF type to corresponding fetch-type string.
+ */
+ tname = traceprobe_type_from_btf(btf, arg->type);
+ if (tname)
+ body = kasprintf(GFP_KERNEL, "$arg%d:%s", i + 1, tname);
+ else
+ body = kasprintf(GFP_KERNEL, "$arg%d", i + 1);
+
+ if (!body)
+ return -ENOMEM;
+ /* Parse fetch argument */
+ ret = traceprobe_parse_probe_arg_body(body, &tp->size, parg,
+ TPARG_FL_KERNEL | TPARG_FL_FENTRY, 0);
+
+ kfree(body);
+
+ return ret;
+}
+#endif
+
int traceprobe_parse_probe_arg(struct trace_probe *tp, int i, const char *arg,
unsigned int flags)
{
diff --git a/kernel/trace/trace_probe.h b/kernel/trace/trace_probe.h
index 355c78a930f8..857b946afe29 100644
--- a/kernel/trace/trace_probe.h
+++ b/kernel/trace/trace_probe.h
@@ -23,6 +23,7 @@
#include <linux/limits.h>
#include <linux/uaccess.h>
#include <linux/bitops.h>
+#include <linux/btf.h>
#include <asm/bitsperlong.h>
#include "trace.h"
@@ -359,6 +360,10 @@ int trace_probe_create(const char *raw_command, int (*createfn)(int, const char
extern int traceprobe_parse_probe_arg(struct trace_probe *tp, int i,
const char *argv, unsigned int flags);
+#ifdef CONFIG_BPF_SYSCALL
+int traceprobe_parse_btf_arg(struct trace_probe *tp, int i, struct btf *btf,
+ const struct btf_param *arg);
+#endif
extern int traceprobe_update_arg(struct probe_arg *arg);
extern void traceprobe_free_probe_arg(struct probe_arg *arg);