[PATCH v2 5/9] tracing/probes: Support BTF field access from $retval
From: Masami Hiramatsu (Google)
Date: Mon Jul 17 2023 - 11:25:22 EST
From: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
Support BTF argument on '$retval' for function return events including
kretprobe and fprobe for accessing the return value.
This also allows user to access its fields if the return value is a
pointer of a data structure.
E.g.
# echo 'f getname_flags%return +0($retval->name):string' \
> dynamic_events
# echo 1 > events/fprobes/getname_flags__exit/enable
# ls > /dev/null
# head -n 40 trace | tail
ls-87 [000] ...1. 8067.616101: getname_flags__exit: (vfs_fstatat+0x3c/0x70 <- getname_flags) arg1="./function_profile_enabled"
ls-87 [000] ...1. 8067.616108: getname_flags__exit: (vfs_fstatat+0x3c/0x70 <- getname_flags) arg1="./trace_stat"
ls-87 [000] ...1. 8067.616115: getname_flags__exit: (vfs_fstatat+0x3c/0x70 <- getname_flags) arg1="./set_graph_notrace"
ls-87 [000] ...1. 8067.616122: getname_flags__exit: (vfs_fstatat+0x3c/0x70 <- getname_flags) arg1="./set_graph_function"
ls-87 [000] ...1. 8067.616129: getname_flags__exit: (vfs_fstatat+0x3c/0x70 <- getname_flags) arg1="./set_ftrace_notrace"
ls-87 [000] ...1. 8067.616135: getname_flags__exit: (vfs_fstatat+0x3c/0x70 <- getname_flags) arg1="./set_ftrace_filter"
ls-87 [000] ...1. 8067.616143: getname_flags__exit: (vfs_fstatat+0x3c/0x70 <- getname_flags) arg1="./touched_functions"
ls-87 [000] ...1. 8067.616237: getname_flags__exit: (vfs_fstatat+0x3c/0x70 <- getname_flags) arg1="./enabled_functions"
ls-87 [000] ...1. 8067.616245: getname_flags__exit: (vfs_fstatat+0x3c/0x70 <- getname_flags) arg1="./available_filter_functions"
ls-87 [000] ...1. 8067.616253: getname_flags__exit: (vfs_fstatat+0x3c/0x70 <- getname_flags) arg1="./set_ftrace_notrace_pid"
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
---
Changes in v2:
- Use '$retval' instead of 'retval' because it is confusing.
---
kernel/trace/trace_probe.c | 98 +++++++++++++++++---------------------------
1 file changed, 37 insertions(+), 61 deletions(-)
diff --git a/kernel/trace/trace_probe.c b/kernel/trace/trace_probe.c
index dd646d35637d..4442ff9c2728 100644
--- a/kernel/trace/trace_probe.c
+++ b/kernel/trace/trace_probe.c
@@ -536,6 +536,22 @@ static int parse_btf_arg(char *varname,
return -EOPNOTSUPP;
}
+ if (ctx->flags & TPARG_FL_RETURN) {
+ if (strcmp(varname, "$retval") != 0) {
+ trace_probe_log_err(ctx->offset, NO_BTFARG);
+ return -ENOENT;
+ }
+ /* Check whether the function return type is not void */
+ type = btf_find_func_proto(btf, ctx->funcname);
+ if (!IS_ERR_OR_NULL(type) && type->type == 0) {
+ trace_probe_log_err(ctx->offset, NO_RETVAL);
+ return -ENOENT;
+ }
+ code->op = FETCH_OP_RETVAL;
+ tid = type->type;
+ goto found;
+ }
+
if (!ctx->params) {
params = find_btf_func_param(ctx->funcname, &ctx->nr_params,
ctx->flags & TPARG_FL_TPOINT);
@@ -556,7 +572,6 @@ static int parse_btf_arg(char *varname,
code->param = i + 1;
else
code->param = i;
-
tid = params[i].type;
goto found;
}
@@ -581,7 +596,7 @@ static int parse_btf_arg(char *varname,
return 0;
}
-static const struct fetch_type *parse_btf_arg_type(
+static const struct fetch_type *find_fetch_type_from_btf_type(
struct traceprobe_parse_context *ctx)
{
struct btf *btf = traceprobe_get_btf();
@@ -593,26 +608,6 @@ static const struct fetch_type *parse_btf_arg_type(
return find_fetch_type(typestr, ctx->flags);
}
-static const struct fetch_type *parse_btf_retval_type(
- struct traceprobe_parse_context *ctx)
-{
- struct btf *btf = traceprobe_get_btf();
- const char *typestr = NULL;
- const struct btf_type *type;
- s32 tid;
-
- if (btf && ctx->funcname) {
- type = btf_find_func_proto(btf, ctx->funcname);
- if (!IS_ERR_OR_NULL(type)) {
- type = btf_type_skip_modifiers(btf, type->type, &tid);
- if (!IS_ERR_OR_NULL(type))
- typestr = fetch_type_from_btf_type(btf, type, ctx);
- }
- }
-
- return find_fetch_type(typestr, ctx->flags);
-}
-
static int parse_btf_bitfield(struct fetch_insn **pcode,
struct traceprobe_parse_context *ctx)
{
@@ -635,20 +630,6 @@ static int parse_btf_bitfield(struct fetch_insn **pcode,
return 0;
}
-static bool is_btf_retval_void(const char *funcname)
-{
- struct btf *btf = traceprobe_get_btf();
- const struct btf_type *t;
-
- if (!btf)
- return false;
-
- t = btf_find_func_proto(btf, funcname);
- if (IS_ERR_OR_NULL(t))
- return false;
-
- return t->type == 0;
-}
#else
static struct btf *traceprobe_get_btf(void)
{
@@ -676,24 +657,23 @@ static int parse_btf_bitfield(struct fetch_insn **pcode,
return -EOPNOTSUPP;
}
-#define parse_btf_arg_type(ctx) \
- find_fetch_type(NULL, ctx->flags)
-
-#define parse_btf_retval_type(ctx) \
+#define find_fetch_type_from_btf_type(ctx) \
find_fetch_type(NULL, ctx->flags)
-#define is_btf_retval_void(funcname) (false)
-
#endif
#define PARAM_MAX_STACK (THREAD_SIZE / sizeof(unsigned long))
-static int parse_probe_vars(char *arg, const struct fetch_type *t,
- struct fetch_insn *code,
+/* Parse $vars. @orig_arg points '$', which syncs to @ctx->offset */
+static int parse_probe_vars(char *orig_arg, const struct fetch_type *t,
+ struct fetch_insn **pcode,
+ struct fetch_insn *end,
struct traceprobe_parse_context *ctx)
{
- unsigned long param;
+ struct fetch_insn *code = *pcode;
int err = TP_ERR_BAD_VAR;
+ char *arg = orig_arg + 1;
+ unsigned long param;
int ret = 0;
int len;
@@ -712,18 +692,17 @@ static int parse_probe_vars(char *arg, const struct fetch_type *t,
goto inval;
}
- if (strcmp(arg, "retval") == 0) {
- if (ctx->flags & TPARG_FL_RETURN) {
- if ((ctx->flags & TPARG_FL_KERNEL) &&
- is_btf_retval_void(ctx->funcname)) {
- err = TP_ERR_NO_RETVAL;
- goto inval;
- }
+ if (str_has_prefix(arg, "retval")) {
+ if (!(ctx->flags & TPARG_FL_RETURN)) {
+ err = TP_ERR_RETVAL_ON_PROBE;
+ goto inval;
+ }
+ if (!(ctx->flags & TPARG_FL_KERNEL) ||
+ !IS_ENABLED(CONFIG_PROBE_EVENTS_BTF_ARGS)) {
code->op = FETCH_OP_RETVAL;
return 0;
}
- err = TP_ERR_RETVAL_ON_PROBE;
- goto inval;
+ return parse_btf_arg(orig_arg, pcode, end, ctx);
}
len = str_has_prefix(arg, "stack");
@@ -825,7 +804,7 @@ parse_probe_arg(char *arg, const struct fetch_type *type,
switch (arg[0]) {
case '$':
- ret = parse_probe_vars(arg + 1, type, code, ctx);
+ ret = parse_probe_vars(arg, type, pcode, end, ctx);
break;
case '%': /* named register */
@@ -1122,12 +1101,9 @@ static int traceprobe_parse_probe_arg_body(const char *argv, ssize_t *size,
goto fail;
/* Update storing type if BTF is available */
- if (IS_ENABLED(CONFIG_PROBE_EVENTS_BTF_ARGS) && !t) {
- if (ctx->last_type)
- parg->type = parse_btf_arg_type(ctx);
- else if (ctx->flags & TPARG_FL_RETURN)
- parg->type = parse_btf_retval_type(ctx);
- }
+ if (IS_ENABLED(CONFIG_PROBE_EVENTS_BTF_ARGS) &&
+ !t && ctx->last_type)
+ parg->type = find_fetch_type_from_btf_type(ctx);
ret = -EINVAL;
/* Store operation */