tracing/probes: Support function parameters if BTF is available

Support function or tracepoint parameters by name if BTF support is enabled
and the event is for function entry (this feature can be used with kprobe-
events, fprobe-events and tracepoint probe events.)

Note that the BTF variable syntax does not require a prefix. If it starts
with an alphabetic character or an underscore ('_') without a prefix like
'$' and '%', it is considered as a BTF variable.
If you specify only the BTF variable name, the argument name will also
be the same name instead of 'arg*'.

 # echo 'p vfs_read count pos' >> dynamic_events
 # echo 'f vfs_write count pos' >> dynamic_events
 # echo 't sched_overutilized_tp rd overutilized' >> dynamic_events
 # cat dynamic_events
p:kprobes/p_vfs_read_0 vfs_read count=count pos=pos
f:fprobes/vfs_write__entry vfs_write count=count pos=pos
t:tracepoints/sched_overutilized_tp sched_overutilized_tp rd=rd overutilized=overutilized

Link: https://lore.kernel.org/all/168507474014.913472.16963996883278039183.stgit@mhiramat.roam.corp.google.com/

Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Reviewed-by: Alan Maguire <alan.maguire@oracle.com>
Tested-by: Alan Maguire <alan.maguire@oracle.com>

1 files changed, 209 insertions, 2 deletions

diff --git a/kernel/trace/trace_probe.c b/kernel/trace/trace_probe.c
index 9ebefacb6372..08c18d9d4cf2 100644
--- a/kernel/trace/trace_probe.c
+++ b/kernel/trace/trace_probe.c
@@ -11,6 +11,8 @@
  */
 #define pr_fmt(fmt)	"trace_probe: " fmt
 
+#include <linux/bpf.h>
+
 #include "trace_probe.h"
 
 #undef C
@@ -300,6 +302,171 @@ static int parse_trace_event_arg(char *arg, struct fetch_insn *code,
 	return -ENOENT;
 }
 
+#ifdef CONFIG_PROBE_EVENTS_BTF_ARGS
+
+static struct btf *traceprobe_get_btf(void)
+{
+	struct btf *btf = bpf_get_btf_vmlinux();
+
+	if (IS_ERR_OR_NULL(btf))
+		return NULL;
+
+	return btf;
+}
+
+static u32 btf_type_int(const struct btf_type *t)
+{
+	return *(u32 *)(t + 1);
+}
+
+static const char *type_from_btf_id(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_ENUM64:
+		return "s64";
+	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";
+			}
+		}
+	}
+	/* TODO: support other types */
+
+	return NULL;
+}
+
+static const struct btf_param *find_btf_func_param(const char *funcname, s32 *nr)
+{
+	struct btf *btf = traceprobe_get_btf();
+	const struct btf_type *t;
+	s32 id;
+
+	if (!btf || !funcname || !nr)
+		return ERR_PTR(-EINVAL);
+
+	id = btf_find_by_name_kind(btf, funcname, BTF_KIND_FUNC);
+	if (id <= 0)
+		return ERR_PTR(-ENOENT);
+
+	/* Get BTF_KIND_FUNC type */
+	t = btf_type_by_id(btf, id);
+	if (!btf_type_is_func(t))
+		return ERR_PTR(-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 ERR_PTR(-ENOENT);
+
+	*nr = btf_type_vlen(t);
+
+	if (*nr)
+		return (const struct btf_param *)(t + 1);
+	else
+		return NULL;
+}
+
+static int parse_btf_arg(const char *varname, struct fetch_insn *code,
+			 struct traceprobe_parse_context *ctx)
+{
+	struct btf *btf = traceprobe_get_btf();
+	const struct btf_param *params;
+	int i;
+
+	if (!btf) {
+		trace_probe_log_err(ctx->offset, NOSUP_BTFARG);
+		return -EOPNOTSUPP;
+	}
+
+	if (WARN_ON_ONCE(!ctx->funcname))
+		return -EINVAL;
+
+	if (!ctx->params) {
+		params = find_btf_func_param(ctx->funcname, &ctx->nr_params);
+		if (IS_ERR(params)) {
+			trace_probe_log_err(ctx->offset, NO_BTF_ENTRY);
+			return PTR_ERR(params);
+		}
+		ctx->params = params;
+	} else
+		params = ctx->params;
+
+	for (i = 0; i < ctx->nr_params; i++) {
+		const char *name = btf_name_by_offset(btf, params[i].name_off);
+
+		if (name && !strcmp(name, varname)) {
+			code->op = FETCH_OP_ARG;
+			code->param = i;
+			return 0;
+		}
+	}
+	trace_probe_log_err(ctx->offset, NO_BTFARG);
+	return -ENOENT;
+}
+
+static const struct fetch_type *parse_btf_arg_type(int arg_idx,
+					struct traceprobe_parse_context *ctx)
+{
+	struct btf *btf = traceprobe_get_btf();
+	const char *typestr = NULL;
+
+	if (btf && ctx->params)
+		typestr = type_from_btf_id(btf, ctx->params[arg_idx].type);
+
+	return find_fetch_type(typestr, ctx->flags);
+}
+#else
+static struct btf *traceprobe_get_btf(void)
+{
+	return NULL;
+}
+
+static int parse_btf_arg(const char *varname, struct fetch_insn *code,
+			 struct traceprobe_parse_context *ctx)
+{
+	trace_probe_log_err(ctx->offset, NOSUP_BTFARG);
+	return -EOPNOTSUPP;
+}
+#define parse_btf_arg_type(idx, ctx)		\
+	find_fetch_type(NULL, ctx->flags)
+#endif
+
 #define PARAM_MAX_STACK (THREAD_SIZE / sizeof(unsigned long))
 
 static int parse_probe_vars(char *arg, const struct fetch_type *t,
@@ -570,6 +737,15 @@ parse_probe_arg(char *arg, const struct fetch_type *type,
 				code->op = FETCH_OP_IMM;
 		}
 		break;
+	default:
+		if (isalpha(arg[0]) || arg[0] == '_') {	/* BTF variable */
+			if (!tparg_is_function_entry(ctx->flags)) {
+				trace_probe_log_err(ctx->offset, NOSUP_BTFARG);
+				return -EINVAL;
+			}
+			ret = parse_btf_arg(arg, code, ctx);
+			break;
+		}
 	}
 	if (!ret && code->op == FETCH_OP_NOP) {
 		/* Parsed, but do not find fetch method */
@@ -718,6 +894,11 @@ static int traceprobe_parse_probe_arg_body(const char *argv, ssize_t *size,
 	if (ret)
 		goto fail;
 
+	/* Update storing type if BTF is available */
+	if (IS_ENABLED(CONFIG_PROBE_EVENTS_BTF_ARGS) &&
+	    !t && code->op == FETCH_OP_ARG)
+		parg->type = parse_btf_arg_type(code->param, ctx);
+
 	ret = -EINVAL;
 	/* Store operation */
 	if (parg->type->is_string) {
@@ -850,6 +1031,33 @@ static int traceprobe_conflict_field_name(const char *name,
 	return 0;
 }
 
+static char *generate_probe_arg_name(const char *arg, int idx)
+{
+	char *name = NULL;
+	const char *end;
+
+	/*
+	 * If argument name is omitted, try arg as a name (BTF variable)
+	 * or "argN".
+	 */
+	if (IS_ENABLED(CONFIG_PROBE_EVENTS_BTF_ARGS)) {
+		end = strchr(arg, ':');
+		if (!end)
+			end = arg + strlen(arg);
+
+		name = kmemdup_nul(arg, end - arg, GFP_KERNEL);
+		if (!name || !is_good_name(name)) {
+			kfree(name);
+			name = NULL;
+		}
+	}
+
+	if (!name)
+		name = kasprintf(GFP_KERNEL, "arg%d", idx + 1);
+
+	return name;
+}
+
 int traceprobe_parse_probe_arg(struct trace_probe *tp, int i, const char *arg,
 			       struct traceprobe_parse_context *ctx)
 {
@@ -871,8 +1079,7 @@ int traceprobe_parse_probe_arg(struct trace_probe *tp, int i, const char *arg,
 		parg->name = kmemdup_nul(arg, body - arg, GFP_KERNEL);
 		body++;
 	} else {
-		/* If argument name is omitted, set "argN" */
-		parg->name = kasprintf(GFP_KERNEL, "arg%d", i + 1);
+		parg->name = generate_probe_arg_name(arg, i);
 		body = arg;
 	}
 	if (!parg->name)