[PATCH v3 0/8] tracing/probes: Support function parameter access from return probe

[PATCH v3 0/8] tracing/probes: Support function parameter access from return probe

[Masami Hiramatsu (Google)]

Hi,

Here is version 3 series of patches to support accessing function entry data
from function *return* probes (including kretprobe and fprobe-exit event).
The previous version is here;

https://lore.kernel.org/all/170891987362.609861.6767830614537418260.stgit@devnote2/

In this version, [1/8] is a bugfix patch (but note that this is already pushed to
probes-fixes-v6.8-rc5, just for reference), updated [4/8] changelog and build error,
fixes selftests error [6/8], update document[8/8] and added Steve's reviewed-by.


This allows us to access the results of some functions, which returns the
error code and its results are passed via function parameter, such as an
structure-initialization function.

For example, vfs_open() will link the file structure to the inode and update
mode. Thus we can trace that changes.

 # echo 'f vfs_open mode=file->f_mode:x32 inode=file->f_inode:x64' >> dynamic_events
 # echo 'f vfs_open%return mode=file->f_mode:x32 inode=file->f_inode:x64' >> dynamic_events 
 # echo 1 > events/fprobes/enable 
 # cat trace
              sh-131     [006] ...1.  1945.714346: vfs_open__entry: (vfs_open+0x4/0x40) mode=0x2 inode=0x0
              sh-131     [006] ...1.  1945.714358: vfs_open__exit: (do_open+0x274/0x3d0 <- vfs_open) mode=0x4d801e inode=0xffff888008470168
             cat-143     [007] ...1.  1945.717949: vfs_open__entry: (vfs_open+0x4/0x40) mode=0x1 inode=0x0
             cat-143     [007] ...1.  1945.717956: vfs_open__exit: (do_open+0x274/0x3d0 <- vfs_open) mode=0x4a801d inode=0xffff888005f78d28
             cat-143     [007] ...1.  1945.720616: vfs_open__entry: (vfs_open+0x4/0x40) mode=0x1 inode=0x0
             cat-143     [007] ...1.  1945.728263: vfs_open__exit: (do_open+0x274/0x3d0 <- vfs_open) mode=0xa800d inode=0xffff888004ada8d8

So as you can see those fields are initialized at exit.

This series is based on v6.8-rc5 kernel or you can checkout from

https://git.kernel.org/pub/scm/linux/kernel/git/mhiramat/linux.git/log/?h=topic/entry-data

Thank you,

---

Masami Hiramatsu (Google) (8):
      fprobe: Fix to allocate entry_data_size buffer with rethook instances
      tracing/fprobe-event: cleanup: Fix a wrong comment in fprobe event
      tracing/probes: Cleanup probe argument parser
      tracing/probes: cleanup: Set trace_probe::nr_args at trace_probe_init
      tracing: Remove redundant #else block for BTF args from README
      tracing/probes: Support $argN in return probe (kprobe and fprobe)
      selftests/ftrace: Add test cases for entry args at function exit
      Documentation: tracing: Add entry argument access at function exit


 Documentation/trace/fprobetrace.rst                |   31 +
 Documentation/trace/kprobetrace.rst                |    9 
 kernel/trace/fprobe.c                              |   14 -
 kernel/trace/trace.c                               |    5 
 kernel/trace/trace_eprobe.c                        |    8 
 kernel/trace/trace_fprobe.c                        |   59 ++-
 kernel/trace/trace_kprobe.c                        |   58 ++-
 kernel/trace/trace_probe.c                         |  417 ++++++++++++++------
 kernel/trace/trace_probe.h                         |   30 +
 kernel/trace/trace_probe_tmpl.h                    |   10 
 kernel/trace/trace_uprobe.c                        |   14 -
 .../ftrace/test.d/dynevent/fprobe_entry_arg.tc     |   18 +
 .../ftrace/test.d/dynevent/fprobe_syntax_errors.tc |    4 
 .../ftrace/test.d/kprobe/kprobe_syntax_errors.tc   |    2 
 .../ftrace/test.d/kprobe/kretprobe_entry_arg.tc    |   18 +
 15 files changed, 521 insertions(+), 176 deletions(-)
 create mode 100644 tools/testing/selftests/ftrace/test.d/dynevent/fprobe_entry_arg.tc
 create mode 100644 tools/testing/selftests/ftrace/test.d/kprobe/kretprobe_entry_arg.tc

--
Masami Hiramatsu (Google) <mhiramat@kernel.org>

[PATCH v3 1/8] fprobe: Fix to allocate entry_data_size buffer with rethook instances

[Masami Hiramatsu (Google)]

From: Masami Hiramatsu (Google) <mhiramat@kernel.org>

Fix to allocate fprobe::entry_data_size buffer with rethook instances.
If fprobe doesn't allocate entry_data_size buffer for each rethook instance,
fprobe entry handler can cause a buffer overrun when storing entry data in
entry handler.

Link: https://lore.kernel.org/all/170920576727.107552.638161246679734051.stgit@devnote2/

Reported-by: Jiri Olsa <olsajiri@gmail.com>
Closes: https://lore.kernel.org/all/Zd9eBn2FTQzYyg7L@krava/
Fixes: 4bbd93455659 ("kprobes: kretprobe scalability improvement")
Cc: stable@vger.kernel.org
Tested-by: Jiri Olsa <olsajiri@gmail.com>
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
---
 kernel/trace/fprobe.c |   14 ++++++--------
 1 file changed, 6 insertions(+), 8 deletions(-)

diff --git a/kernel/trace/fprobe.c b/kernel/trace/fprobe.c
index 6cd2a4e3afb8..9ff018245840 100644
--- a/kernel/trace/fprobe.c
+++ b/kernel/trace/fprobe.c
@@ -189,9 +189,6 @@ static int fprobe_init_rethook(struct fprobe *fp, int num)
 {
 	int size;
 
-	if (num <= 0)
-		return -EINVAL;
-
 	if (!fp->exit_handler) {
 		fp->rethook = NULL;
 		return 0;
@@ -199,15 +196,16 @@ static int fprobe_init_rethook(struct fprobe *fp, int num)
 
 	/* Initialize rethook if needed */
 	if (fp->nr_maxactive)
-		size = fp->nr_maxactive;
+		num = fp->nr_maxactive;
 	else
-		size = num * num_possible_cpus() * 2;
-	if (size <= 0)
+		num *= num_possible_cpus() * 2;
+	if (num <= 0)
 		return -EINVAL;
 
+	size = sizeof(struct fprobe_rethook_node) + fp->entry_data_size;
+
 	/* Initialize rethook */
-	fp->rethook = rethook_alloc((void *)fp, fprobe_exit_handler,
-				sizeof(struct fprobe_rethook_node), size);
+	fp->rethook = rethook_alloc((void *)fp, fprobe_exit_handler, size, num);
 	if (IS_ERR(fp->rethook))
 		return PTR_ERR(fp->rethook);
 

[PATCH v3 2/8] tracing/fprobe-event: cleanup: Fix a wrong comment in fprobe event

[Masami Hiramatsu (Google)]

From: Masami Hiramatsu (Google) <mhiramat@kernel.org>

Despite the fprobe event,  "Kretprobe" was commented. So fix it.

Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
 kernel/trace/trace_fprobe.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/trace/trace_fprobe.c b/kernel/trace/trace_fprobe.c
index 7d2ddbcfa377..3ccef4d82235 100644
--- a/kernel/trace/trace_fprobe.c
+++ b/kernel/trace/trace_fprobe.c
@@ -210,7 +210,7 @@ fentry_trace_func(struct trace_fprobe *tf, unsigned long entry_ip,
 }
 NOKPROBE_SYMBOL(fentry_trace_func);
 
-/* Kretprobe handler */
+/* function exit handler */
 static nokprobe_inline void
 __fexit_trace_func(struct trace_fprobe *tf, unsigned long entry_ip,
 		   unsigned long ret_ip, struct pt_regs *regs,

[PATCH v3 3/8] tracing/probes: Cleanup probe argument parser

[Masami Hiramatsu (Google)]

From: Masami Hiramatsu (Google) <mhiramat@kernel.org>

Cleanup traceprobe_parse_probe_arg_body() to split out the
type parser and post-processing part of fetch_insn.
This makes no functional change.

Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
 kernel/trace/trace_probe.c |  230 ++++++++++++++++++++++++++------------------
 1 file changed, 137 insertions(+), 93 deletions(-)

diff --git a/kernel/trace/trace_probe.c b/kernel/trace/trace_probe.c
index 34289f9c6707..67a0b9cbb648 100644
--- a/kernel/trace/trace_probe.c
+++ b/kernel/trace/trace_probe.c
@@ -1090,67 +1090,45 @@ static int __parse_bitfield_probe_arg(const char *bf,
 	return (BYTES_TO_BITS(t->size) < (bw + bo)) ? -EINVAL : 0;
 }
 
-/* String length checking wrapper */
-static int traceprobe_parse_probe_arg_body(const char *argv, ssize_t *size,
-					   struct probe_arg *parg,
-					   struct traceprobe_parse_context *ctx)
+/* Split type part from @arg and return it. */
+static char *parse_probe_arg_type(char *arg, struct probe_arg *parg,
+				  struct traceprobe_parse_context *ctx)
 {
-	struct fetch_insn *code, *scode, *tmp = NULL;
-	char *t, *t2, *t3;
-	int ret, len;
-	char *arg;
+	char *t = NULL, *t2, *t3;
+	int offs;
 
-	arg = kstrdup(argv, GFP_KERNEL);
-	if (!arg)
-		return -ENOMEM;
-
-	ret = -EINVAL;
-	len = strlen(arg);
-	if (len > MAX_ARGSTR_LEN) {
-		trace_probe_log_err(ctx->offset, ARG_TOO_LONG);
-		goto out;
-	} else if (len == 0) {
-		trace_probe_log_err(ctx->offset, NO_ARG_BODY);
-		goto out;
-	}
-
-	ret = -ENOMEM;
-	parg->comm = kstrdup(arg, GFP_KERNEL);
-	if (!parg->comm)
-		goto out;
-
-	ret = -EINVAL;
 	t = strchr(arg, ':');
 	if (t) {
-		*t = '\0';
-		t2 = strchr(++t, '[');
+		*t++ = '\0';
+		t2 = strchr(t, '[');
 		if (t2) {
 			*t2++ = '\0';
 			t3 = strchr(t2, ']');
 			if (!t3) {
-				int offs = t2 + strlen(t2) - arg;
+				offs = t2 + strlen(t2) - arg;
 
 				trace_probe_log_err(ctx->offset + offs,
 						    ARRAY_NO_CLOSE);
-				goto out;
+				return ERR_PTR(-EINVAL);
 			} else if (t3[1] != '\0') {
 				trace_probe_log_err(ctx->offset + t3 + 1 - arg,
 						    BAD_ARRAY_SUFFIX);
-				goto out;
+				return ERR_PTR(-EINVAL);
 			}
 			*t3 = '\0';
 			if (kstrtouint(t2, 0, &parg->count) || !parg->count) {
 				trace_probe_log_err(ctx->offset + t2 - arg,
 						    BAD_ARRAY_NUM);
-				goto out;
+				return ERR_PTR(-EINVAL);
 			}
 			if (parg->count > MAX_ARRAY_LEN) {
 				trace_probe_log_err(ctx->offset + t2 - arg,
 						    ARRAY_TOO_BIG);
-				goto out;
+				return ERR_PTR(-EINVAL);
 			}
 		}
 	}
+	offs = t ? t - arg : 0;
 
 	/*
 	 * Since $comm and immediate string can not be dereferenced,
@@ -1161,74 +1139,52 @@ static int traceprobe_parse_probe_arg_body(const char *argv, ssize_t *size,
 	     strncmp(arg, "\\\"", 2) == 0)) {
 		/* The type of $comm must be "string", and not an array type. */
 		if (parg->count || (t && strcmp(t, "string"))) {
-			trace_probe_log_err(ctx->offset + (t ? (t - arg) : 0),
-					NEED_STRING_TYPE);
-			goto out;
+			trace_probe_log_err(ctx->offset + offs, NEED_STRING_TYPE);
+			return ERR_PTR(-EINVAL);
 		}
 		parg->type = find_fetch_type("string", ctx->flags);
 	} else
 		parg->type = find_fetch_type(t, ctx->flags);
+
 	if (!parg->type) {
-		trace_probe_log_err(ctx->offset + (t ? (t - arg) : 0), BAD_TYPE);
-		goto out;
+		trace_probe_log_err(ctx->offset + offs, BAD_TYPE);
+		return ERR_PTR(-EINVAL);
 	}
 
-	code = tmp = kcalloc(FETCH_INSN_MAX, sizeof(*code), GFP_KERNEL);
-	if (!code)
-		goto out;
-	code[FETCH_INSN_MAX - 1].op = FETCH_OP_END;
-
-	ctx->last_type = NULL;
-	ret = parse_probe_arg(arg, parg->type, &code, &code[FETCH_INSN_MAX - 1],
-			      ctx);
-	if (ret)
-		goto fail;
-
-	/* Update storing type if BTF is available */
-	if (IS_ENABLED(CONFIG_PROBE_EVENTS_BTF_ARGS) &&
-	    ctx->last_type) {
-		if (!t) {
-			parg->type = find_fetch_type_from_btf_type(ctx);
-		} else if (strstr(t, "string")) {
-			ret = check_prepare_btf_string_fetch(t, &code, ctx);
-			if (ret)
-				goto fail;
-		}
-	}
-	parg->offset = *size;
-	*size += parg->type->size * (parg->count ?: 1);
+	return t;
+}
 
-	if (parg->count) {
-		len = strlen(parg->type->fmttype) + 6;
-		parg->fmt = kmalloc(len, GFP_KERNEL);
-		if (!parg->fmt) {
-			ret = -ENOMEM;
-			goto out;
-		}
-		snprintf(parg->fmt, len, "%s[%d]", parg->type->fmttype,
-			 parg->count);
-	}
+/* After parsing, adjust the fetch_insn according to the probe_arg */
+static int finalize_fetch_insn(struct fetch_insn *code,
+			       struct probe_arg *parg,
+			       char *type,
+			       int type_offset,
+			       struct traceprobe_parse_context *ctx)
+{
+	struct fetch_insn *scode;
+	int ret;
 
-	ret = -EINVAL;
 	/* Store operation */
 	if (parg->type->is_string) {
+		/* Check bad combination of the type and the last fetch_insn. */
 		if (!strcmp(parg->type->name, "symstr")) {
 			if (code->op != FETCH_OP_REG && code->op != FETCH_OP_STACK &&
 			    code->op != FETCH_OP_RETVAL && code->op != FETCH_OP_ARG &&
 			    code->op != FETCH_OP_DEREF && code->op != FETCH_OP_TP_ARG) {
-				trace_probe_log_err(ctx->offset + (t ? (t - arg) : 0),
+				trace_probe_log_err(ctx->offset + type_offset,
 						    BAD_SYMSTRING);
-				goto fail;
+				return -EINVAL;
 			}
 		} else {
 			if (code->op != FETCH_OP_DEREF && code->op != FETCH_OP_UDEREF &&
 			    code->op != FETCH_OP_IMM && code->op != FETCH_OP_COMM &&
 			    code->op != FETCH_OP_DATA && code->op != FETCH_OP_TP_ARG) {
-				trace_probe_log_err(ctx->offset + (t ? (t - arg) : 0),
+				trace_probe_log_err(ctx->offset + type_offset,
 						    BAD_STRING);
-				goto fail;
+				return -EINVAL;
 			}
 		}
+
 		if (!strcmp(parg->type->name, "symstr") ||
 		    (code->op == FETCH_OP_IMM || code->op == FETCH_OP_COMM ||
 		     code->op == FETCH_OP_DATA) || code->op == FETCH_OP_TP_ARG ||
@@ -1244,9 +1200,10 @@ static int traceprobe_parse_probe_arg_body(const char *argv, ssize_t *size,
 			code++;
 			if (code->op != FETCH_OP_NOP) {
 				trace_probe_log_err(ctx->offset, TOO_MANY_OPS);
-				goto fail;
+				return -EINVAL;
 			}
 		}
+
 		/* If op == DEREF, replace it with STRING */
 		if (!strcmp(parg->type->name, "ustring") ||
 		    code->op == FETCH_OP_UDEREF)
@@ -1267,47 +1224,134 @@ static int traceprobe_parse_probe_arg_body(const char *argv, ssize_t *size,
 		code++;
 		if (code->op != FETCH_OP_NOP) {
 			trace_probe_log_err(ctx->offset, TOO_MANY_OPS);
-			goto fail;
+			return -E2BIG;
 		}
 		code->op = FETCH_OP_ST_RAW;
 		code->size = parg->type->size;
 	}
+
+	/* Save storing fetch_insn. */
 	scode = code;
+
 	/* Modify operation */
-	if (t != NULL) {
-		ret = __parse_bitfield_probe_arg(t, parg->type, &code);
+	if (type != NULL) {
+		/* Bitfield needs a special fetch_insn. */
+		ret = __parse_bitfield_probe_arg(type, parg->type, &code);
 		if (ret) {
-			trace_probe_log_err(ctx->offset + t - arg, BAD_BITFIELD);
-			goto fail;
+			trace_probe_log_err(ctx->offset + type_offset, BAD_BITFIELD);
+			return ret;
 		}
 	} else if (IS_ENABLED(CONFIG_PROBE_EVENTS_BTF_ARGS) &&
 		   ctx->last_type) {
+		/* If user not specified the type, try parsing BTF bitfield. */
 		ret = parse_btf_bitfield(&code, ctx);
 		if (ret)
-			goto fail;
+			return ret;
 	}
-	ret = -EINVAL;
+
 	/* Loop(Array) operation */
 	if (parg->count) {
 		if (scode->op != FETCH_OP_ST_MEM &&
 		    scode->op != FETCH_OP_ST_STRING &&
 		    scode->op != FETCH_OP_ST_USTRING) {
-			trace_probe_log_err(ctx->offset + (t ? (t - arg) : 0),
-					    BAD_STRING);
-			goto fail;
+			trace_probe_log_err(ctx->offset + type_offset, BAD_STRING);
+			return -EINVAL;
 		}
 		code++;
 		if (code->op != FETCH_OP_NOP) {
 			trace_probe_log_err(ctx->offset, TOO_MANY_OPS);
-			goto fail;
+			return -E2BIG;
 		}
 		code->op = FETCH_OP_LP_ARRAY;
 		code->param = parg->count;
 	}
+
+	/* Finalize the fetch_insn array. */
 	code++;
 	code->op = FETCH_OP_END;
 
-	ret = 0;
+	return 0;
+}
+
+/* String length checking wrapper */
+static int traceprobe_parse_probe_arg_body(const char *argv, ssize_t *size,
+					   struct probe_arg *parg,
+					   struct traceprobe_parse_context *ctx)
+{
+	struct fetch_insn *code, *tmp = NULL;
+	char *type, *arg;
+	int ret, len;
+
+	len = strlen(argv);
+	if (len > MAX_ARGSTR_LEN) {
+		trace_probe_log_err(ctx->offset, ARG_TOO_LONG);
+		return -E2BIG;
+	} else if (len == 0) {
+		trace_probe_log_err(ctx->offset, NO_ARG_BODY);
+		return -EINVAL;
+	}
+
+	arg = kstrdup(argv, GFP_KERNEL);
+	if (!arg)
+		return -ENOMEM;
+
+	parg->comm = kstrdup(arg, GFP_KERNEL);
+	if (!parg->comm) {
+		ret = -ENOMEM;
+		goto out;
+	}
+
+	type = parse_probe_arg_type(arg, parg, ctx);
+	if (IS_ERR(type)) {
+		ret = PTR_ERR(type);
+		goto out;
+	}
+
+	code = tmp = kcalloc(FETCH_INSN_MAX, sizeof(*code), GFP_KERNEL);
+	if (!code) {
+		ret = -ENOMEM;
+		goto out;
+	}
+	code[FETCH_INSN_MAX - 1].op = FETCH_OP_END;
+
+	ctx->last_type = NULL;
+	ret = parse_probe_arg(arg, parg->type, &code, &code[FETCH_INSN_MAX - 1],
+			      ctx);
+	if (ret < 0)
+		goto fail;
+
+	/* Update storing type if BTF is available */
+	if (IS_ENABLED(CONFIG_PROBE_EVENTS_BTF_ARGS) &&
+	    ctx->last_type) {
+		if (!type) {
+			parg->type = find_fetch_type_from_btf_type(ctx);
+		} else if (strstr(type, "string")) {
+			ret = check_prepare_btf_string_fetch(type, &code, ctx);
+			if (ret)
+				goto fail;
+		}
+	}
+	parg->offset = *size;
+	*size += parg->type->size * (parg->count ?: 1);
+
+	if (parg->count) {
+		len = strlen(parg->type->fmttype) + 6;
+		parg->fmt = kmalloc(len, GFP_KERNEL);
+		if (!parg->fmt) {
+			ret = -ENOMEM;
+			goto out;
+		}
+		snprintf(parg->fmt, len, "%s[%d]", parg->type->fmttype,
+			 parg->count);
+	}
+
+	ret = finalize_fetch_insn(code, parg, type, type ? type - arg : 0, ctx);
+	if (ret < 0)
+		goto fail;
+
+	for (; code < tmp + FETCH_INSN_MAX; code++)
+		if (code->op == FETCH_OP_END)
+			break;
 	/* Shrink down the code buffer */
 	parg->code = kcalloc(code - tmp + 1, sizeof(*code), GFP_KERNEL);
 	if (!parg->code)
@@ -1316,7 +1360,7 @@ static int traceprobe_parse_probe_arg_body(const char *argv, ssize_t *size,
 		memcpy(parg->code, tmp, sizeof(*code) * (code - tmp + 1));
 
 fail:
-	if (ret) {
+	if (ret < 0) {
 		for (code = tmp; code < tmp + FETCH_INSN_MAX; code++)
 			if (code->op == FETCH_NOP_SYMBOL ||
 			    code->op == FETCH_OP_DATA)

[PATCH v3 4/8] tracing/probes: cleanup: Set trace_probe::nr_args at trace_probe_init

[Masami Hiramatsu (Google)]

From: Masami Hiramatsu (Google) <mhiramat@kernel.org>

Instead of incrementing the trace_probe::nr_args, init it at
trace_probe_init(). Without this change, there is no way to get the number
of trace_probe arguments while parsing it.
This is a cleanup, so the behavior is not changed.

Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
---
 Changes in v3:
  - Fix build error in trace_{kprobe,fprobe}.c.
  - Update changelog.
---
 kernel/trace/trace_eprobe.c |    2 +-
 kernel/trace/trace_fprobe.c |    2 +-
 kernel/trace/trace_kprobe.c |    2 +-
 kernel/trace/trace_probe.c  |   10 ++++++----
 kernel/trace/trace_probe.h  |    2 +-
 kernel/trace/trace_uprobe.c |    2 +-
 6 files changed, 11 insertions(+), 9 deletions(-)

diff --git a/kernel/trace/trace_eprobe.c b/kernel/trace/trace_eprobe.c
index 03c851f57969..eb72def7410f 100644
--- a/kernel/trace/trace_eprobe.c
+++ b/kernel/trace/trace_eprobe.c
@@ -220,7 +220,7 @@ static struct trace_eprobe *alloc_event_probe(const char *group,
 	if (!ep->event_system)
 		goto error;
 
-	ret = trace_probe_init(&ep->tp, this_event, group, false);
+	ret = trace_probe_init(&ep->tp, this_event, group, false, nargs);
 	if (ret < 0)
 		goto error;
 
diff --git a/kernel/trace/trace_fprobe.c b/kernel/trace/trace_fprobe.c
index 3ccef4d82235..5109650b0d82 100644
--- a/kernel/trace/trace_fprobe.c
+++ b/kernel/trace/trace_fprobe.c
@@ -389,7 +389,7 @@ static struct trace_fprobe *alloc_trace_fprobe(const char *group,
 	tf->tpoint = tpoint;
 	tf->fp.nr_maxactive = maxactive;
 
-	ret = trace_probe_init(&tf->tp, event, group, false);
+	ret = trace_probe_init(&tf->tp, event, group, false, nargs);
 	if (ret < 0)
 		goto error;
 
diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
index c4c6e0e0068b..843f13f839df 100644
--- a/kernel/trace/trace_kprobe.c
+++ b/kernel/trace/trace_kprobe.c
@@ -290,7 +290,7 @@ static struct trace_kprobe *alloc_trace_kprobe(const char *group,
 	INIT_HLIST_NODE(&tk->rp.kp.hlist);
 	INIT_LIST_HEAD(&tk->rp.kp.list);
 
-	ret = trace_probe_init(&tk->tp, event, group, false);
+	ret = trace_probe_init(&tk->tp, event, group, false, nargs);
 	if (ret < 0)
 		goto error;
 
diff --git a/kernel/trace/trace_probe.c b/kernel/trace/trace_probe.c
index 67a0b9cbb648..93f36f8a108e 100644
--- a/kernel/trace/trace_probe.c
+++ b/kernel/trace/trace_probe.c
@@ -1423,9 +1423,6 @@ int traceprobe_parse_probe_arg(struct trace_probe *tp, int i, const char *arg,
 	struct probe_arg *parg = &tp->args[i];
 	const char *body;
 
-	/* Increment count for freeing args in error case */
-	tp->nr_args++;
-
 	body = strchr(arg, '=');
 	if (body) {
 		if (body - arg > MAX_ARG_NAME_LEN) {
@@ -1810,7 +1807,7 @@ void trace_probe_cleanup(struct trace_probe *tp)
 }
 
 int trace_probe_init(struct trace_probe *tp, const char *event,
-		     const char *group, bool alloc_filter)
+		     const char *group, bool alloc_filter, int nargs)
 {
 	struct trace_event_call *call;
 	size_t size = sizeof(struct trace_probe_event);
@@ -1846,6 +1843,11 @@ int trace_probe_init(struct trace_probe *tp, const char *event,
 		goto error;
 	}
 
+	tp->nr_args = nargs;
+	/* Make sure pointers in args[] are NULL */
+	if (nargs)
+		memset(tp->args, 0, sizeof(tp->args[0]) * nargs);
+
 	return 0;
 
 error:
diff --git a/kernel/trace/trace_probe.h b/kernel/trace/trace_probe.h
index c1877d018269..ed8d1052f8a7 100644
--- a/kernel/trace/trace_probe.h
+++ b/kernel/trace/trace_probe.h
@@ -338,7 +338,7 @@ static inline bool trace_probe_has_single_file(struct trace_probe *tp)
 }
 
 int trace_probe_init(struct trace_probe *tp, const char *event,
-		     const char *group, bool alloc_filter);
+		     const char *group, bool alloc_filter, int nargs);
 void trace_probe_cleanup(struct trace_probe *tp);
 int trace_probe_append(struct trace_probe *tp, struct trace_probe *to);
 void trace_probe_unlink(struct trace_probe *tp);
diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c
index a84b85d8aac1..796ebcae9b38 100644
--- a/kernel/trace/trace_uprobe.c
+++ b/kernel/trace/trace_uprobe.c
@@ -337,7 +337,7 @@ alloc_trace_uprobe(const char *group, const char *event, int nargs, bool is_ret)
 	if (!tu)
 		return ERR_PTR(-ENOMEM);
 
-	ret = trace_probe_init(&tu->tp, event, group, true);
+	ret = trace_probe_init(&tu->tp, event, group, true, nargs);
 	if (ret < 0)
 		goto error;
 

[PATCH v3 5/8] tracing: Remove redundant #else block for BTF args from README

[Masami Hiramatsu (Google)]

From: Masami Hiramatsu (Google) <mhiramat@kernel.org>

Remove redundant #else block for BTF args from README message.
This is a cleanup, so no change on the message.

Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
 kernel/trace/trace.c |    4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 8198bfc54b58..516c585f5879 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -5747,11 +5747,9 @@ static const char readme_msg[] =
 	"\t     args: <name>=fetcharg[:type]\n"
 	"\t fetcharg: (%<register>|$<efield>), @<address>, @<symbol>[+|-<offset>],\n"
 #ifdef CONFIG_HAVE_FUNCTION_ARG_ACCESS_API
-#ifdef CONFIG_PROBE_EVENTS_BTF_ARGS
 	"\t           $stack<index>, $stack, $retval, $comm, $arg<N>,\n"
+#ifdef CONFIG_PROBE_EVENTS_BTF_ARGS
 	"\t           <argname>[->field[->field|.field...]],\n"
-#else
-	"\t           $stack<index>, $stack, $retval, $comm, $arg<N>,\n"
 #endif
 #else
 	"\t           $stack<index>, $stack, $retval, $comm,\n"

[PATCH v3 6/8] tracing/probes: Support $argN in return probe (kprobe and fprobe)

[Masami Hiramatsu (Google)]

From: Masami Hiramatsu (Google) <mhiramat@kernel.org>

Support accessing $argN in the return probe events. This will help users to
record entry data in function return (exit) event for simplfing the function
entry/exit information in one event, and record the result values (e.g.
allocated object/initialized object) at function exit.

For example, if we have a function `int init_foo(struct foo *obj, int param)`
sometimes we want to check how `obj` is initialized. In such case, we can
define a new return event like below;

 # echo 'r init_foo retval=$retval param=$arg2 field1=+0($arg1)' >> kprobe_events

Thus it records the function parameter `param` and its result `obj->field1`
(the dereference will be done in the function exit timing) value at once.

This also support fprobe, BTF args and'$arg*'. So if CONFIG_DEBUG_INFO_BTF
is enabled, we can trace both function parameters and the return value
by following command.

 # echo 'f target_function%return $arg* $retval' >> dynamic_events

Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
---
 Changes in v3:
   - Fix syntax error check selftests because now some syntax error
     will not happen.
 Changes in v2:
   - Update README message
---
 kernel/trace/trace.c                               |    1 
 kernel/trace/trace_eprobe.c                        |    6 -
 kernel/trace/trace_fprobe.c                        |   55 ++++--
 kernel/trace/trace_kprobe.c                        |   56 +++++-
 kernel/trace/trace_probe.c                         |  177 ++++++++++++++++++--
 kernel/trace/trace_probe.h                         |   28 +++
 kernel/trace/trace_probe_tmpl.h                    |   10 +
 kernel/trace/trace_uprobe.c                        |   12 +
 .../ftrace/test.d/dynevent/fprobe_syntax_errors.tc |    4 
 .../ftrace/test.d/kprobe/kprobe_syntax_errors.tc   |    2 
 10 files changed, 289 insertions(+), 62 deletions(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 516c585f5879..71a96decc276 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -5755,6 +5755,7 @@ static const char readme_msg[] =
 	"\t           $stack<index>, $stack, $retval, $comm,\n"
 #endif
 	"\t           +|-[u]<offset>(<fetcharg>), \\imm-value, \\\"imm-string\"\n"
+	"\t     kernel return probes support: $retval, $arg<N>, $comm\n"
 	"\t     type: s8/16/32/64, u8/16/32/64, x8/16/32/64, char, string, symbol,\n"
 	"\t           b<bit-width>@<bit-offset>/<container-size>, ustring,\n"
 	"\t           symstr, <type>\\[<array-size>\\]\n"
diff --git a/kernel/trace/trace_eprobe.c b/kernel/trace/trace_eprobe.c
index eb72def7410f..b0e0ec85912e 100644
--- a/kernel/trace/trace_eprobe.c
+++ b/kernel/trace/trace_eprobe.c
@@ -390,8 +390,8 @@ static int get_eprobe_size(struct trace_probe *tp, void *rec)
 
 /* Note that we don't verify it, since the code does not come from user space */
 static int
-process_fetch_insn(struct fetch_insn *code, void *rec, void *dest,
-		   void *base)
+process_fetch_insn(struct fetch_insn *code, void *rec, void *edata,
+		   void *dest, void *base)
 {
 	unsigned long val;
 	int ret;
@@ -438,7 +438,7 @@ __eprobe_trace_func(struct eprobe_data *edata, void *rec)
 		return;
 
 	entry = fbuffer.entry = ring_buffer_event_data(fbuffer.event);
-	store_trace_args(&entry[1], &edata->ep->tp, rec, sizeof(*entry), dsize);
+	store_trace_args(&entry[1], &edata->ep->tp, rec, NULL, sizeof(*entry), dsize);
 
 	trace_event_buffer_commit(&fbuffer);
 }
diff --git a/kernel/trace/trace_fprobe.c b/kernel/trace/trace_fprobe.c
index 5109650b0d82..4f4280815522 100644
--- a/kernel/trace/trace_fprobe.c
+++ b/kernel/trace/trace_fprobe.c
@@ -4,6 +4,7 @@
  * Copyright (C) 2022 Google LLC.
  */
 #define pr_fmt(fmt)	"trace_fprobe: " fmt
+#include <asm/ptrace.h>
 
 #include <linux/fprobe.h>
 #include <linux/module.h>
@@ -129,8 +130,8 @@ static bool trace_fprobe_is_registered(struct trace_fprobe *tf)
  * from user space.
  */
 static int
-process_fetch_insn(struct fetch_insn *code, void *rec, void *dest,
-		   void *base)
+process_fetch_insn(struct fetch_insn *code, void *rec, void *edata,
+		   void *dest, void *base)
 {
 	struct pt_regs *regs = rec;
 	unsigned long val;
@@ -152,6 +153,9 @@ process_fetch_insn(struct fetch_insn *code, void *rec, void *dest,
 	case FETCH_OP_ARG:
 		val = regs_get_kernel_argument(regs, code->param);
 		break;
+	case FETCH_OP_EDATA:
+		val = *(unsigned long *)((unsigned long)edata + code->offset);
+		break;
 #endif
 	case FETCH_NOP_SYMBOL:	/* Ignore a place holder */
 		code++;
@@ -184,7 +188,7 @@ __fentry_trace_func(struct trace_fprobe *tf, unsigned long entry_ip,
 	if (trace_trigger_soft_disabled(trace_file))
 		return;
 
-	dsize = __get_data_size(&tf->tp, regs);
+	dsize = __get_data_size(&tf->tp, regs, NULL);
 
 	entry = trace_event_buffer_reserve(&fbuffer, trace_file,
 					   sizeof(*entry) + tf->tp.size + dsize);
@@ -194,7 +198,7 @@ __fentry_trace_func(struct trace_fprobe *tf, unsigned long entry_ip,
 	fbuffer.regs = regs;
 	entry = fbuffer.entry = ring_buffer_event_data(fbuffer.event);
 	entry->ip = entry_ip;
-	store_trace_args(&entry[1], &tf->tp, regs, sizeof(*entry), dsize);
+	store_trace_args(&entry[1], &tf->tp, regs, NULL, sizeof(*entry), dsize);
 
 	trace_event_buffer_commit(&fbuffer);
 }
@@ -211,10 +215,23 @@ fentry_trace_func(struct trace_fprobe *tf, unsigned long entry_ip,
 NOKPROBE_SYMBOL(fentry_trace_func);
 
 /* function exit handler */
+static int trace_fprobe_entry_handler(struct fprobe *fp, unsigned long entry_ip,
+				unsigned long ret_ip, struct pt_regs *regs,
+				void *entry_data)
+{
+	struct trace_fprobe *tf = container_of(fp, struct trace_fprobe, fp);
+
+	if (tf->tp.entry_arg)
+		store_trace_entry_data(entry_data, &tf->tp, regs);
+
+	return 0;
+}
+NOKPROBE_SYMBOL(trace_fprobe_entry_handler)
+
 static nokprobe_inline void
 __fexit_trace_func(struct trace_fprobe *tf, unsigned long entry_ip,
 		   unsigned long ret_ip, struct pt_regs *regs,
-		   struct trace_event_file *trace_file)
+		   void *entry_data, struct trace_event_file *trace_file)
 {
 	struct fexit_trace_entry_head *entry;
 	struct trace_event_buffer fbuffer;
@@ -227,7 +244,7 @@ __fexit_trace_func(struct trace_fprobe *tf, unsigned long entry_ip,
 	if (trace_trigger_soft_disabled(trace_file))
 		return;
 
-	dsize = __get_data_size(&tf->tp, regs);
+	dsize = __get_data_size(&tf->tp, regs, entry_data);
 
 	entry = trace_event_buffer_reserve(&fbuffer, trace_file,
 					   sizeof(*entry) + tf->tp.size + dsize);
@@ -238,19 +255,19 @@ __fexit_trace_func(struct trace_fprobe *tf, unsigned long entry_ip,
 	entry = fbuffer.entry = ring_buffer_event_data(fbuffer.event);
 	entry->func = entry_ip;
 	entry->ret_ip = ret_ip;
-	store_trace_args(&entry[1], &tf->tp, regs, sizeof(*entry), dsize);
+	store_trace_args(&entry[1], &tf->tp, regs, entry_data, sizeof(*entry), dsize);
 
 	trace_event_buffer_commit(&fbuffer);
 }
 
 static void
 fexit_trace_func(struct trace_fprobe *tf, unsigned long entry_ip,
-		 unsigned long ret_ip, struct pt_regs *regs)
+		 unsigned long ret_ip, struct pt_regs *regs, void *entry_data)
 {
 	struct event_file_link *link;
 
 	trace_probe_for_each_link_rcu(link, &tf->tp)
-		__fexit_trace_func(tf, entry_ip, ret_ip, regs, link->file);
+		__fexit_trace_func(tf, entry_ip, ret_ip, regs, entry_data, link->file);
 }
 NOKPROBE_SYMBOL(fexit_trace_func);
 
@@ -269,7 +286,7 @@ static int fentry_perf_func(struct trace_fprobe *tf, unsigned long entry_ip,
 	if (hlist_empty(head))
 		return 0;
 
-	dsize = __get_data_size(&tf->tp, regs);
+	dsize = __get_data_size(&tf->tp, regs, NULL);
 	__size = sizeof(*entry) + tf->tp.size + dsize;
 	size = ALIGN(__size + sizeof(u32), sizeof(u64));
 	size -= sizeof(u32);
@@ -280,7 +297,7 @@ static int fentry_perf_func(struct trace_fprobe *tf, unsigned long entry_ip,
 
 	entry->ip = entry_ip;
 	memset(&entry[1], 0, dsize);
-	store_trace_args(&entry[1], &tf->tp, regs, sizeof(*entry), dsize);
+	store_trace_args(&entry[1], &tf->tp, regs, NULL, sizeof(*entry), dsize);
 	perf_trace_buf_submit(entry, size, rctx, call->event.type, 1, regs,
 			      head, NULL);
 	return 0;
@@ -289,7 +306,8 @@ NOKPROBE_SYMBOL(fentry_perf_func);
 
 static void
 fexit_perf_func(struct trace_fprobe *tf, unsigned long entry_ip,
-		unsigned long ret_ip, struct pt_regs *regs)
+		unsigned long ret_ip, struct pt_regs *regs,
+		void *entry_data)
 {
 	struct trace_event_call *call = trace_probe_event_call(&tf->tp);
 	struct fexit_trace_entry_head *entry;
@@ -301,7 +319,7 @@ fexit_perf_func(struct trace_fprobe *tf, unsigned long entry_ip,
 	if (hlist_empty(head))
 		return;
 
-	dsize = __get_data_size(&tf->tp, regs);
+	dsize = __get_data_size(&tf->tp, regs, entry_data);
 	__size = sizeof(*entry) + tf->tp.size + dsize;
 	size = ALIGN(__size + sizeof(u32), sizeof(u64));
 	size -= sizeof(u32);
@@ -312,7 +330,7 @@ fexit_perf_func(struct trace_fprobe *tf, unsigned long entry_ip,
 
 	entry->func = entry_ip;
 	entry->ret_ip = ret_ip;
-	store_trace_args(&entry[1], &tf->tp, regs, sizeof(*entry), dsize);
+	store_trace_args(&entry[1], &tf->tp, regs, entry_data, sizeof(*entry), dsize);
 	perf_trace_buf_submit(entry, size, rctx, call->event.type, 1, regs,
 			      head, NULL);
 }
@@ -343,10 +361,10 @@ static void fexit_dispatcher(struct fprobe *fp, unsigned long entry_ip,
 	struct trace_fprobe *tf = container_of(fp, struct trace_fprobe, fp);
 
 	if (trace_probe_test_flag(&tf->tp, TP_FLAG_TRACE))
-		fexit_trace_func(tf, entry_ip, ret_ip, regs);
+		fexit_trace_func(tf, entry_ip, ret_ip, regs, entry_data);
 #ifdef CONFIG_PERF_EVENTS
 	if (trace_probe_test_flag(&tf->tp, TP_FLAG_PROFILE))
-		fexit_perf_func(tf, entry_ip, ret_ip, regs);
+		fexit_perf_func(tf, entry_ip, ret_ip, regs, entry_data);
 #endif
 }
 NOKPROBE_SYMBOL(fexit_dispatcher);
@@ -1109,6 +1127,11 @@ static int __trace_fprobe_create(int argc, const char *argv[])
 			goto error;	/* This can be -ENOMEM */
 	}
 
+	if (is_return && tf->tp.entry_arg) {
+		tf->fp.entry_handler = trace_fprobe_entry_handler;
+		tf->fp.entry_data_size = traceprobe_get_entry_data_size(&tf->tp);
+	}
+
 	ret = traceprobe_set_print_fmt(&tf->tp,
 			is_return ? PROBE_PRINT_RETURN : PROBE_PRINT_NORMAL);
 	if (ret < 0)
diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
index 843f13f839df..14099cc17fc9 100644
--- a/kernel/trace/trace_kprobe.c
+++ b/kernel/trace/trace_kprobe.c
@@ -740,6 +740,9 @@ static unsigned int number_of_same_symbols(char *func_name)
 	return ctx.count;
 }
 
+static int trace_kprobe_entry_handler(struct kretprobe_instance *ri,
+				      struct pt_regs *regs);
+
 static int __trace_kprobe_create(int argc, const char *argv[])
 {
 	/*
@@ -948,6 +951,11 @@ static int __trace_kprobe_create(int argc, const char *argv[])
 		if (ret)
 			goto error;	/* This can be -ENOMEM */
 	}
+	/* entry handler for kretprobe */
+	if (is_return && tk->tp.entry_arg) {
+		tk->rp.entry_handler = trace_kprobe_entry_handler;
+		tk->rp.data_size = traceprobe_get_entry_data_size(&tk->tp);
+	}
 
 	ptype = is_return ? PROBE_PRINT_RETURN : PROBE_PRINT_NORMAL;
 	ret = traceprobe_set_print_fmt(&tk->tp, ptype);
@@ -1303,8 +1311,8 @@ static const struct file_operations kprobe_profile_ops = {
 
 /* Note that we don't verify it, since the code does not come from user space */
 static int
-process_fetch_insn(struct fetch_insn *code, void *rec, void *dest,
-		   void *base)
+process_fetch_insn(struct fetch_insn *code, void *rec, void *edata,
+		   void *dest, void *base)
 {
 	struct pt_regs *regs = rec;
 	unsigned long val;
@@ -1329,6 +1337,9 @@ process_fetch_insn(struct fetch_insn *code, void *rec, void *dest,
 	case FETCH_OP_ARG:
 		val = regs_get_kernel_argument(regs, code->param);
 		break;
+	case FETCH_OP_EDATA:
+		val = *(unsigned long *)((unsigned long)edata + code->offset);
+		break;
 #endif
 	case FETCH_NOP_SYMBOL:	/* Ignore a place holder */
 		code++;
@@ -1359,7 +1370,7 @@ __kprobe_trace_func(struct trace_kprobe *tk, struct pt_regs *regs,
 	if (trace_trigger_soft_disabled(trace_file))
 		return;
 
-	dsize = __get_data_size(&tk->tp, regs);
+	dsize = __get_data_size(&tk->tp, regs, NULL);
 
 	entry = trace_event_buffer_reserve(&fbuffer, trace_file,
 					   sizeof(*entry) + tk->tp.size + dsize);
@@ -1368,7 +1379,7 @@ __kprobe_trace_func(struct trace_kprobe *tk, struct pt_regs *regs,
 
 	fbuffer.regs = regs;
 	entry->ip = (unsigned long)tk->rp.kp.addr;
-	store_trace_args(&entry[1], &tk->tp, regs, sizeof(*entry), dsize);
+	store_trace_args(&entry[1], &tk->tp, regs, NULL, sizeof(*entry), dsize);
 
 	trace_event_buffer_commit(&fbuffer);
 }
@@ -1384,6 +1395,31 @@ kprobe_trace_func(struct trace_kprobe *tk, struct pt_regs *regs)
 NOKPROBE_SYMBOL(kprobe_trace_func);
 
 /* Kretprobe handler */
+
+static int trace_kprobe_entry_handler(struct kretprobe_instance *ri,
+				      struct pt_regs *regs)
+{
+	struct kretprobe *rp = get_kretprobe(ri);
+	struct trace_kprobe *tk;
+
+	/*
+	 * There is a small chance that get_kretprobe(ri) returns NULL when
+	 * the kretprobe is unregister on another CPU between kretprobe's
+	 * trampoline_handler and this function.
+	 */
+	if (unlikely(!rp))
+		return -ENOENT;
+
+	tk = container_of(rp, struct trace_kprobe, rp);
+
+	/* store argument values into ri->data as entry data */
+	if (tk->tp.entry_arg)
+		store_trace_entry_data(ri->data, &tk->tp, regs);
+
+	return 0;
+}
+
+
 static nokprobe_inline void
 __kretprobe_trace_func(struct trace_kprobe *tk, struct kretprobe_instance *ri,
 		       struct pt_regs *regs,
@@ -1399,7 +1435,7 @@ __kretprobe_trace_func(struct trace_kprobe *tk, struct kretprobe_instance *ri,
 	if (trace_trigger_soft_disabled(trace_file))
 		return;
 
-	dsize = __get_data_size(&tk->tp, regs);
+	dsize = __get_data_size(&tk->tp, regs, ri->data);
 
 	entry = trace_event_buffer_reserve(&fbuffer, trace_file,
 					   sizeof(*entry) + tk->tp.size + dsize);
@@ -1409,7 +1445,7 @@ __kretprobe_trace_func(struct trace_kprobe *tk, struct kretprobe_instance *ri,
 	fbuffer.regs = regs;
 	entry->func = (unsigned long)tk->rp.kp.addr;
 	entry->ret_ip = get_kretprobe_retaddr(ri);
-	store_trace_args(&entry[1], &tk->tp, regs, sizeof(*entry), dsize);
+	store_trace_args(&entry[1], &tk->tp, regs, ri->data, sizeof(*entry), dsize);
 
 	trace_event_buffer_commit(&fbuffer);
 }
@@ -1557,7 +1593,7 @@ kprobe_perf_func(struct trace_kprobe *tk, struct pt_regs *regs)
 	if (hlist_empty(head))
 		return 0;
 
-	dsize = __get_data_size(&tk->tp, regs);
+	dsize = __get_data_size(&tk->tp, regs, NULL);
 	__size = sizeof(*entry) + tk->tp.size + dsize;
 	size = ALIGN(__size + sizeof(u32), sizeof(u64));
 	size -= sizeof(u32);
@@ -1568,7 +1604,7 @@ kprobe_perf_func(struct trace_kprobe *tk, struct pt_regs *regs)
 
 	entry->ip = (unsigned long)tk->rp.kp.addr;
 	memset(&entry[1], 0, dsize);
-	store_trace_args(&entry[1], &tk->tp, regs, sizeof(*entry), dsize);
+	store_trace_args(&entry[1], &tk->tp, regs, NULL, sizeof(*entry), dsize);
 	perf_trace_buf_submit(entry, size, rctx, call->event.type, 1, regs,
 			      head, NULL);
 	return 0;
@@ -1593,7 +1629,7 @@ kretprobe_perf_func(struct trace_kprobe *tk, struct kretprobe_instance *ri,
 	if (hlist_empty(head))
 		return;
 
-	dsize = __get_data_size(&tk->tp, regs);
+	dsize = __get_data_size(&tk->tp, regs, ri->data);
 	__size = sizeof(*entry) + tk->tp.size + dsize;
 	size = ALIGN(__size + sizeof(u32), sizeof(u64));
 	size -= sizeof(u32);
@@ -1604,7 +1640,7 @@ kretprobe_perf_func(struct trace_kprobe *tk, struct kretprobe_instance *ri,
 
 	entry->func = (unsigned long)tk->rp.kp.addr;
 	entry->ret_ip = get_kretprobe_retaddr(ri);
-	store_trace_args(&entry[1], &tk->tp, regs, sizeof(*entry), dsize);
+	store_trace_args(&entry[1], &tk->tp, regs, ri->data, sizeof(*entry), dsize);
 	perf_trace_buf_submit(entry, size, rctx, call->event.type, 1, regs,
 			      head, NULL);
 }
diff --git a/kernel/trace/trace_probe.c b/kernel/trace/trace_probe.c
index 93f36f8a108e..217169de0920 100644
--- a/kernel/trace/trace_probe.c
+++ b/kernel/trace/trace_probe.c
@@ -594,6 +594,8 @@ static int parse_btf_field(char *fieldname, const struct btf_type *type,
 	return 0;
 }
 
+static int __store_entry_arg(struct trace_probe *tp, int argnum);
+
 static int parse_btf_arg(char *varname,
 			 struct fetch_insn **pcode, struct fetch_insn *end,
 			 struct traceprobe_parse_context *ctx)
@@ -618,11 +620,7 @@ static int parse_btf_arg(char *varname,
 		return -EOPNOTSUPP;
 	}
 
-	if (ctx->flags & TPARG_FL_RETURN) {
-		if (strcmp(varname, "$retval") != 0) {
-			trace_probe_log_err(ctx->offset, NO_BTFARG);
-			return -ENOENT;
-		}
+	if (ctx->flags & TPARG_FL_RETURN && !strcmp(varname, "$retval")) {
 		code->op = FETCH_OP_RETVAL;
 		/* Check whether the function return type is not void */
 		if (query_btf_context(ctx) == 0) {
@@ -654,11 +652,21 @@ static int parse_btf_arg(char *varname,
 		const char *name = btf_name_by_offset(ctx->btf, params[i].name_off);
 
 		if (name && !strcmp(name, varname)) {
-			code->op = FETCH_OP_ARG;
-			if (ctx->flags & TPARG_FL_TPOINT)
-				code->param = i + 1;
-			else
-				code->param = i;
+			if (tparg_is_function_entry(ctx->flags)) {
+				code->op = FETCH_OP_ARG;
+				if (ctx->flags & TPARG_FL_TPOINT)
+					code->param = i + 1;
+				else
+					code->param = i;
+			} else if (tparg_is_function_return(ctx->flags)) {
+				code->op = FETCH_OP_EDATA;
+				ret = __store_entry_arg(ctx->tp, i);
+				if (ret < 0) {
+					/* internal error */
+					return ret;
+				}
+				code->offset = ret;
+			}
 			tid = params[i].type;
 			goto found;
 		}
@@ -755,6 +763,110 @@ static int check_prepare_btf_string_fetch(char *typename,
 
 #endif
 
+#ifdef CONFIG_HAVE_FUNCTION_ARG_ACCESS_API
+
+static int __store_entry_arg(struct trace_probe *tp, int argnum)
+{
+	struct probe_entry_arg *earg = tp->entry_arg;
+	bool match = false;
+	int i, offset;
+
+	if (!earg) {
+		earg = kzalloc(sizeof(*tp->entry_arg), GFP_KERNEL);
+		if (!earg)
+			return -ENOMEM;
+		earg->size = 2 * tp->nr_args + 1;
+		earg->code = kcalloc(earg->size, sizeof(struct fetch_insn),
+				     GFP_KERNEL);
+		if (!earg->code) {
+			kfree(earg);
+			return -ENOMEM;
+		}
+		/* Fill the code buffer with 'end' to simplify it */
+		for (i = 0; i < earg->size; i++)
+			earg->code[i].op = FETCH_OP_END;
+		tp->entry_arg = earg;
+	}
+
+	offset = 0;
+	for (i = 0; i < earg->size - 1; i++) {
+		switch (earg->code[i].op) {
+		case FETCH_OP_END:
+			earg->code[i].op = FETCH_OP_ARG;
+			earg->code[i].param = argnum;
+			earg->code[i + 1].op = FETCH_OP_ST_EDATA;
+			earg->code[i + 1].offset = offset;
+			return offset;
+		case FETCH_OP_ARG:
+			match = (earg->code[i].param == argnum);
+			break;
+		case FETCH_OP_ST_EDATA:
+			offset = earg->code[i].offset;
+			if (match)
+				return offset;
+			offset += sizeof(unsigned long);
+			break;
+		default:
+			break;
+		}
+	}
+	return -ENOSPC;
+}
+
+int traceprobe_get_entry_data_size(struct trace_probe *tp)
+{
+	struct probe_entry_arg *earg = tp->entry_arg;
+	int i, size = 0;
+
+	if (!earg)
+		return 0;
+
+	for (i = 0; i < earg->size; i++) {
+		switch (earg->code[i].op) {
+		case FETCH_OP_END:
+			goto out;
+		case FETCH_OP_ST_EDATA:
+			size = earg->code[i].offset + sizeof(unsigned long);
+			break;
+		default:
+			break;
+		}
+	}
+out:
+	return size;
+}
+
+void store_trace_entry_data(void *edata, struct trace_probe *tp, struct pt_regs *regs)
+{
+	struct probe_entry_arg *earg = tp->entry_arg;
+	unsigned long val;
+	int i;
+
+	if (!earg)
+		return;
+
+	for (i = 0; i < earg->size; i++) {
+		struct fetch_insn *code = &earg->code[i];
+
+		switch (code->op) {
+		case FETCH_OP_ARG:
+			val = regs_get_kernel_argument(regs, code->param);
+			break;
+		case FETCH_OP_ST_EDATA:
+			*(unsigned long *)((unsigned long)edata + code->offset) = val;
+			break;
+		case FETCH_OP_END:
+			goto end;
+		default:
+			break;
+		}
+	}
+end:
+	return;
+}
+NOKPROBE_SYMBOL(store_trace_entry_data)
+#endif
+
 #define PARAM_MAX_STACK (THREAD_SIZE / sizeof(unsigned long))
 
 /* Parse $vars. @orig_arg points '$', which syncs to @ctx->offset */
@@ -830,7 +942,7 @@ static int parse_probe_vars(char *orig_arg, const struct fetch_type *t,
 
 #ifdef CONFIG_HAVE_FUNCTION_ARG_ACCESS_API
 	len = str_has_prefix(arg, "arg");
-	if (len && tparg_is_function_entry(ctx->flags)) {
+	if (len) {
 		ret = kstrtoul(arg + len, 10, &param);
 		if (ret)
 			goto inval;
@@ -839,15 +951,29 @@ static int parse_probe_vars(char *orig_arg, const struct fetch_type *t,
 			err = TP_ERR_BAD_ARG_NUM;
 			goto inval;
 		}
+		param--; /* argN starts from 1, but internal arg[N] starts from 0 */
 
-		code->op = FETCH_OP_ARG;
-		code->param = (unsigned int)param - 1;
-		/*
-		 * The tracepoint probe will probe a stub function, and the
-		 * first parameter of the stub is a dummy and should be ignored.
-		 */
-		if (ctx->flags & TPARG_FL_TPOINT)
-			code->param++;
+		if (tparg_is_function_entry(ctx->flags)) {
+			code->op = FETCH_OP_ARG;
+			code->param = (unsigned int)param;
+			/*
+			 * The tracepoint probe will probe a stub function, and the
+			 * first parameter of the stub is a dummy and should be ignored.
+			 */
+			if (ctx->flags & TPARG_FL_TPOINT)
+				code->param++;
+		} else if (tparg_is_function_return(ctx->flags)) {
+			/* function entry argument access from return probe */
+			ret = __store_entry_arg(ctx->tp, param);
+			if (ret < 0)	/* This error should be an internal error */
+				return ret;
+
+			code->op = FETCH_OP_EDATA;
+			code->offset = ret;
+		} else {
+			err = TP_ERR_NOFENTRY_ARGS;
+			goto inval;
+		}
 		return 0;
 	}
 #endif
@@ -1037,7 +1163,8 @@ parse_probe_arg(char *arg, const struct fetch_type *type,
 		break;
 	default:
 		if (isalpha(arg[0]) || arg[0] == '_') {	/* BTF variable */
-			if (!tparg_is_function_entry(ctx->flags)) {
+			if (!tparg_is_function_entry(ctx->flags) &&
+			    !tparg_is_function_return(ctx->flags)) {
 				trace_probe_log_err(ctx->offset, NOSUP_BTFARG);
 				return -EINVAL;
 			}
@@ -1423,6 +1550,7 @@ int traceprobe_parse_probe_arg(struct trace_probe *tp, int i, const char *arg,
 	struct probe_arg *parg = &tp->args[i];
 	const char *body;
 
+	ctx->tp = tp;
 	body = strchr(arg, '=');
 	if (body) {
 		if (body - arg > MAX_ARG_NAME_LEN) {
@@ -1479,7 +1607,8 @@ static int argv_has_var_arg(int argc, const char *argv[], int *args_idx,
 		if (str_has_prefix(argv[i], "$arg")) {
 			trace_probe_log_set_index(i + 2);
 
-			if (!tparg_is_function_entry(ctx->flags)) {
+			if (!tparg_is_function_entry(ctx->flags) &&
+			    !tparg_is_function_return(ctx->flags)) {
 				trace_probe_log_err(0, NOFENTRY_ARGS);
 				return -EINVAL;
 			}
@@ -1802,6 +1931,12 @@ void trace_probe_cleanup(struct trace_probe *tp)
 	for (i = 0; i < tp->nr_args; i++)
 		traceprobe_free_probe_arg(&tp->args[i]);
 
+	if (tp->entry_arg) {
+		kfree(tp->entry_arg->code);
+		kfree(tp->entry_arg);
+		tp->entry_arg = NULL;
+	}
+
 	if (tp->event)
 		trace_probe_unlink(tp);
 }
diff --git a/kernel/trace/trace_probe.h b/kernel/trace/trace_probe.h
index ed8d1052f8a7..cef3a50628a3 100644
--- a/kernel/trace/trace_probe.h
+++ b/kernel/trace/trace_probe.h
@@ -92,6 +92,7 @@ enum fetch_op {
 	FETCH_OP_ARG,		/* Function argument : .param */
 	FETCH_OP_FOFFS,		/* File offset: .immediate */
 	FETCH_OP_DATA,		/* Allocated data: .data */
+	FETCH_OP_EDATA,		/* Entry data: .offset */
 	// Stage 2 (dereference) op
 	FETCH_OP_DEREF,		/* Dereference: .offset */
 	FETCH_OP_UDEREF,	/* User-space Dereference: .offset */
@@ -102,6 +103,7 @@ enum fetch_op {
 	FETCH_OP_ST_STRING,	/* String: .offset, .size */
 	FETCH_OP_ST_USTRING,	/* User String: .offset, .size */
 	FETCH_OP_ST_SYMSTR,	/* Kernel Symbol String: .offset, .size */
+	FETCH_OP_ST_EDATA,	/* Store Entry Data: .offset */
 	// Stage 4 (modify) op
 	FETCH_OP_MOD_BF,	/* Bitfield: .basesize, .lshift, .rshift */
 	// Stage 5 (loop) op
@@ -232,6 +234,11 @@ struct probe_arg {
 	const struct fetch_type	*type;	/* Type of this argument */
 };
 
+struct probe_entry_arg {
+	struct fetch_insn	*code;
+	unsigned int		size;	/* The entry data size */
+};
+
 struct trace_uprobe_filter {
 	rwlock_t		rwlock;
 	int			nr_systemwide;
@@ -253,6 +260,7 @@ struct trace_probe {
 	struct trace_probe_event	*event;
 	ssize_t				size;	/* trace entry size */
 	unsigned int			nr_args;
+	struct probe_entry_arg		*entry_arg;	/* This is only for return probe */
 	struct probe_arg		args[];
 };
 
@@ -355,6 +363,18 @@ int trace_probe_create(const char *raw_command, int (*createfn)(int, const char
 int trace_probe_print_args(struct trace_seq *s, struct probe_arg *args, int nr_args,
 		 u8 *data, void *field);
 
+#ifdef CONFIG_HAVE_FUNCTION_ARG_ACCESS_API
+int traceprobe_get_entry_data_size(struct trace_probe *tp);
+/* This is a runtime function to store entry data */
+void store_trace_entry_data(void *edata, struct trace_probe *tp, struct pt_regs *regs);
+#else /* !CONFIG_HAVE_FUNCTION_ARG_ACCESS_API */
+static inline int traceprobe_get_entry_data_size(struct trace_probe *tp)
+{
+	return 0;
+}
+#define store_trace_entry_data(edata, tp, regs) do { } while (0)
+#endif
+
 #define trace_probe_for_each_link(pos, tp)	\
 	list_for_each_entry(pos, &(tp)->event->files, list)
 #define trace_probe_for_each_link_rcu(pos, tp)	\
@@ -381,6 +401,11 @@ static inline bool tparg_is_function_entry(unsigned int flags)
 	return (flags & TPARG_FL_LOC_MASK) == (TPARG_FL_KERNEL | TPARG_FL_FENTRY);
 }
 
+static inline bool tparg_is_function_return(unsigned int flags)
+{
+	return (flags & TPARG_FL_LOC_MASK) == (TPARG_FL_KERNEL | TPARG_FL_RETURN);
+}
+
 struct traceprobe_parse_context {
 	struct trace_event_call *event;
 	/* BTF related parameters */
@@ -392,6 +417,7 @@ struct traceprobe_parse_context {
 	const struct btf_type *last_type;	/* Saved type */
 	u32 last_bitoffs;		/* Saved bitoffs */
 	u32 last_bitsize;		/* Saved bitsize */
+	struct trace_probe *tp;
 	unsigned int flags;
 	int offset;
 };
@@ -506,7 +532,7 @@ extern int traceprobe_define_arg_fields(struct trace_event_call *event_call,
 	C(NO_BTFARG,		"This variable is not found at this probe point"),\
 	C(NO_BTF_ENTRY,		"No BTF entry for this probe point"),	\
 	C(BAD_VAR_ARGS,		"$arg* must be an independent parameter without name etc."),\
-	C(NOFENTRY_ARGS,	"$arg* can be used only on function entry"),	\
+	C(NOFENTRY_ARGS,	"$arg* can be used only on function entry or exit"),	\
 	C(DOUBLE_ARGS,		"$arg* can be used only once in the parameters"),	\
 	C(ARGS_2LONG,		"$arg* failed because the argument list is too long"),	\
 	C(ARGIDX_2BIG,		"$argN index is too big"),		\
diff --git a/kernel/trace/trace_probe_tmpl.h b/kernel/trace/trace_probe_tmpl.h
index 3935b347f874..2caf0d2afb32 100644
--- a/kernel/trace/trace_probe_tmpl.h
+++ b/kernel/trace/trace_probe_tmpl.h
@@ -54,7 +54,7 @@ fetch_apply_bitfield(struct fetch_insn *code, void *buf)
  * If dest is NULL, don't store result and return required dynamic data size.
  */
 static int
-process_fetch_insn(struct fetch_insn *code, void *rec,
+process_fetch_insn(struct fetch_insn *code, void *rec, void *edata,
 		   void *dest, void *base);
 static nokprobe_inline int fetch_store_strlen(unsigned long addr);
 static nokprobe_inline int
@@ -232,7 +232,7 @@ process_fetch_insn_bottom(struct fetch_insn *code, unsigned long val,
 
 /* Sum up total data length for dynamic arrays (strings) */
 static nokprobe_inline int
-__get_data_size(struct trace_probe *tp, struct pt_regs *regs)
+__get_data_size(struct trace_probe *tp, struct pt_regs *regs, void *edata)
 {
 	struct probe_arg *arg;
 	int i, len, ret = 0;
@@ -240,7 +240,7 @@ __get_data_size(struct trace_probe *tp, struct pt_regs *regs)
 	for (i = 0; i < tp->nr_args; i++) {
 		arg = tp->args + i;
 		if (unlikely(arg->dynamic)) {
-			len = process_fetch_insn(arg->code, regs, NULL, NULL);
+			len = process_fetch_insn(arg->code, regs, edata, NULL, NULL);
 			if (len > 0)
 				ret += len;
 		}
@@ -251,7 +251,7 @@ __get_data_size(struct trace_probe *tp, struct pt_regs *regs)
 
 /* Store the value of each argument */
 static nokprobe_inline void
-store_trace_args(void *data, struct trace_probe *tp, void *rec,
+store_trace_args(void *data, struct trace_probe *tp, void *rec, void *edata,
 		 int header_size, int maxlen)
 {
 	struct probe_arg *arg;
@@ -266,7 +266,7 @@ store_trace_args(void *data, struct trace_probe *tp, void *rec,
 		/* Point the dynamic data area if needed */
 		if (unlikely(arg->dynamic))
 			*dl = make_data_loc(maxlen, dyndata - base);
-		ret = process_fetch_insn(arg->code, rec, dl, base);
+		ret = process_fetch_insn(arg->code, rec, edata, dl, base);
 		if (arg->dynamic && likely(ret > 0)) {
 			dyndata += ret;
 			maxlen -= ret;
diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c
index 796ebcae9b38..9e461362450a 100644
--- a/kernel/trace/trace_uprobe.c
+++ b/kernel/trace/trace_uprobe.c
@@ -211,8 +211,8 @@ static unsigned long translate_user_vaddr(unsigned long file_offset)
 
 /* Note that we don't verify it, since the code does not come from user space */
 static int
-process_fetch_insn(struct fetch_insn *code, void *rec, void *dest,
-		   void *base)
+process_fetch_insn(struct fetch_insn *code, void *rec, void *edata,
+		   void *dest, void *base)
 {
 	struct pt_regs *regs = rec;
 	unsigned long val;
@@ -1490,11 +1490,11 @@ static int uprobe_dispatcher(struct uprobe_consumer *con, struct pt_regs *regs)
 	if (WARN_ON_ONCE(!uprobe_cpu_buffer))
 		return 0;
 
-	dsize = __get_data_size(&tu->tp, regs);
+	dsize = __get_data_size(&tu->tp, regs, NULL);
 	esize = SIZEOF_TRACE_ENTRY(is_ret_probe(tu));
 
 	ucb = uprobe_buffer_get();
-	store_trace_args(ucb->buf, &tu->tp, regs, esize, dsize);
+	store_trace_args(ucb->buf, &tu->tp, regs, NULL, esize, dsize);
 
 	if (trace_probe_test_flag(&tu->tp, TP_FLAG_TRACE))
 		ret |= uprobe_trace_func(tu, regs, ucb, dsize);
@@ -1525,11 +1525,11 @@ static int uretprobe_dispatcher(struct uprobe_consumer *con,
 	if (WARN_ON_ONCE(!uprobe_cpu_buffer))
 		return 0;
 
-	dsize = __get_data_size(&tu->tp, regs);
+	dsize = __get_data_size(&tu->tp, regs, NULL);
 	esize = SIZEOF_TRACE_ENTRY(is_ret_probe(tu));
 
 	ucb = uprobe_buffer_get();
-	store_trace_args(ucb->buf, &tu->tp, regs, esize, dsize);
+	store_trace_args(ucb->buf, &tu->tp, regs, NULL, esize, dsize);
 
 	if (trace_probe_test_flag(&tu->tp, TP_FLAG_TRACE))
 		uretprobe_trace_func(tu, func, regs, ucb, dsize);
diff --git a/tools/testing/selftests/ftrace/test.d/dynevent/fprobe_syntax_errors.tc b/tools/testing/selftests/ftrace/test.d/dynevent/fprobe_syntax_errors.tc
index 20e42c030095..61877d166451 100644
--- a/tools/testing/selftests/ftrace/test.d/dynevent/fprobe_syntax_errors.tc
+++ b/tools/testing/selftests/ftrace/test.d/dynevent/fprobe_syntax_errors.tc
@@ -34,7 +34,9 @@ check_error 'f vfs_read ^$stack10000'	# BAD_STACK_NUM
 
 check_error 'f vfs_read ^$arg10000'	# BAD_ARG_NUM
 
+if !grep -q 'kernel return probes support:' README; then
 check_error 'f vfs_read $retval ^$arg1' # BAD_VAR
+fi
 check_error 'f vfs_read ^$none_var'	# BAD_VAR
 check_error 'f vfs_read ^'$REG		# BAD_VAR
 
@@ -99,7 +101,9 @@ if grep -q "<argname>" README; then
 check_error 'f vfs_read args=^$arg*'		# BAD_VAR_ARGS
 check_error 'f vfs_read +0(^$arg*)'		# BAD_VAR_ARGS
 check_error 'f vfs_read $arg* ^$arg*'		# DOUBLE_ARGS
+if !grep -q 'kernel return probes support:' README; then
 check_error 'f vfs_read%return ^$arg*'		# NOFENTRY_ARGS
+fi
 check_error 'f vfs_read ^hoge'			# NO_BTFARG
 check_error 'f kfree ^$arg10'			# NO_BTFARG (exceed the number of parameters)
 check_error 'f kfree%return ^$retval'		# NO_RETVAL
diff --git a/tools/testing/selftests/ftrace/test.d/kprobe/kprobe_syntax_errors.tc b/tools/testing/selftests/ftrace/test.d/kprobe/kprobe_syntax_errors.tc
index 65fbb26fd58c..a16c6a6f6055 100644
--- a/tools/testing/selftests/ftrace/test.d/kprobe/kprobe_syntax_errors.tc
+++ b/tools/testing/selftests/ftrace/test.d/kprobe/kprobe_syntax_errors.tc
@@ -108,7 +108,9 @@ if grep -q "<argname>" README; then
 check_error 'p vfs_read args=^$arg*'		# BAD_VAR_ARGS
 check_error 'p vfs_read +0(^$arg*)'		# BAD_VAR_ARGS
 check_error 'p vfs_read $arg* ^$arg*'		# DOUBLE_ARGS
+if !grep -q 'kernel return probes support:' README; then
 check_error 'r vfs_read ^$arg*'			# NOFENTRY_ARGS
+fi
 check_error 'p vfs_read+8 ^$arg*'		# NOFENTRY_ARGS
 check_error 'p vfs_read ^hoge'			# NO_BTFARG
 check_error 'p kfree ^$arg10'			# NO_BTFARG (exceed the number of parameters)

[PATCH v3 7/8] selftests/ftrace: Add test cases for entry args at function exit

[Masami Hiramatsu (Google)]

From: Masami Hiramatsu (Google) <mhiramat@kernel.org>

Add kretprobe and function exit probe test cases for checking whether
those can access entry arguments at function exit correctly.

Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
---
 .../ftrace/test.d/dynevent/fprobe_entry_arg.tc     |   18 ++++++++++++++++++
 .../ftrace/test.d/kprobe/kretprobe_entry_arg.tc    |   18 ++++++++++++++++++
 2 files changed, 36 insertions(+)
 create mode 100644 tools/testing/selftests/ftrace/test.d/dynevent/fprobe_entry_arg.tc
 create mode 100644 tools/testing/selftests/ftrace/test.d/kprobe/kretprobe_entry_arg.tc

diff --git a/tools/testing/selftests/ftrace/test.d/dynevent/fprobe_entry_arg.tc b/tools/testing/selftests/ftrace/test.d/dynevent/fprobe_entry_arg.tc
new file mode 100644
index 000000000000..d183b8a8ecf8
--- /dev/null
+++ b/tools/testing/selftests/ftrace/test.d/dynevent/fprobe_entry_arg.tc
@@ -0,0 +1,18 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+# description: Function return probe entry argument access
+# requires: dynamic_events 'f[:[<group>/][<event>]] <func-name>':README 'kernel return probes support:':README
+
+echo 'f:tests/myevent1 vfs_open arg=$arg1' >> dynamic_events
+echo 'f:tests/myevent2 vfs_open%return arg=$arg1' >> dynamic_events
+
+echo 1 > events/tests/enable
+
+echo > trace
+cat trace > /dev/null
+
+function streq() {
+	test $1 = $2
+}
+
+streq `grep -A 1 -m 1 myevent1 trace | sed -r 's/^.*(arg=.*)/\1/' `
diff --git a/tools/testing/selftests/ftrace/test.d/kprobe/kretprobe_entry_arg.tc b/tools/testing/selftests/ftrace/test.d/kprobe/kretprobe_entry_arg.tc
new file mode 100644
index 000000000000..53b82f36a1d0
--- /dev/null
+++ b/tools/testing/selftests/ftrace/test.d/kprobe/kretprobe_entry_arg.tc
@@ -0,0 +1,18 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+# description: Kretprobe entry argument access
+# requires: kprobe_events 'kernel return probes support:':README
+
+echo 'p:myevent1 vfs_open arg=$arg1' >> kprobe_events
+echo 'r:myevent2 vfs_open arg=$arg1' >> kprobe_events
+
+echo 1 > events/kprobes/enable
+
+echo > trace
+cat trace > /dev/null
+
+function streq() {
+	test $1 = $2
+}
+
+streq `grep -A 1 -m 1 myevent1 trace | sed -r 's/^.*(arg=.*)/\1/' `

[PATCH v3 8/8] Documentation: tracing: Add entry argument access at function exit

[Masami Hiramatsu (Google)]

From: Masami Hiramatsu (Google) <mhiramat@kernel.org>

Add a notes about the entry argument access at function exit probes for
kprobes and fprobe trace event.

Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
---
 Changes in v3:
  - Add usage example in fprobetrace.rst.
---
 Documentation/trace/fprobetrace.rst |   31 +++++++++++++++++++++++++++++++
 Documentation/trace/kprobetrace.rst |    9 +++++++++
 2 files changed, 40 insertions(+)

diff --git a/Documentation/trace/fprobetrace.rst b/Documentation/trace/fprobetrace.rst
index e35e6b18df40..0f187e3796e4 100644
--- a/Documentation/trace/fprobetrace.rst
+++ b/Documentation/trace/fprobetrace.rst
@@ -70,6 +70,14 @@ Synopsis of fprobe-events
 
 For the details of TYPE, see :ref:`kprobetrace documentation <kprobetrace_types>`.
 
+Function arguments at exit
+--------------------------
+Function arguments can be accessed at exit probe using $arg<N> fetcharg. This
+is useful to record the function parameter and return value at once, and
+trace the difference of structure fields (for debuging a function whether it
+correctly updates the given data structure or not)
+See the :ref:`sample<fprobetrace_exit_args_sample>` below for how it works.
+
 BTF arguments
 -------------
 BTF (BPF Type Format) argument allows user to trace function and tracepoint
@@ -218,3 +226,26 @@ traceprobe event, you can trace that field as below.
            <idle>-0       [000] d..3.  5606.690317: sched_switch: (__probestub_sched_switch+0x4/0x10) comm="kworker/0:1" usage=1 start_time=137000000
       kworker/0:1-14      [000] d..3.  5606.690339: sched_switch: (__probestub_sched_switch+0x4/0x10) comm="swapper/0" usage=2 start_time=0
            <idle>-0       [000] d..3.  5606.692368: sched_switch: (__probestub_sched_switch+0x4/0x10) comm="kworker/0:1" usage=1 start_time=137000000
+
+.. _fprobetrace_exit_args_sample:
+
+The return probe allows us to access the results of some functions, which returns
+the error code and its results are passed via function parameter, such as an
+structure-initialization function.
+
+For example, vfs_open() will link the file structure to the inode and update
+mode. You can trace that changes with return probe.
+::
+
+ # echo 'f vfs_open mode=file->f_mode:x32 inode=file->f_inode:x64' >> dynamic_events
+ # echo 'f vfs_open%%return mode=file->f_mode:x32 inode=file->f_inode:x64' >> dynamic_events
+ # echo 1 > events/fprobes/enable
+ # cat trace
+              sh-131     [006] ...1.  1945.714346: vfs_open__entry: (vfs_open+0x4/0x40) mode=0x2 inode=0x0
+              sh-131     [006] ...1.  1945.714358: vfs_open__exit: (do_open+0x274/0x3d0 <- vfs_open) mode=0x4d801e inode=0xffff888008470168
+             cat-143     [007] ...1.  1945.717949: vfs_open__entry: (vfs_open+0x4/0x40) mode=0x1 inode=0x0
+             cat-143     [007] ...1.  1945.717956: vfs_open__exit: (do_open+0x274/0x3d0 <- vfs_open) mode=0x4a801d inode=0xffff888005f78d28
+             cat-143     [007] ...1.  1945.720616: vfs_open__entry: (vfs_open+0x4/0x40) mode=0x1 inode=0x0
+             cat-143     [007] ...1.  1945.728263: vfs_open__exit: (do_open+0x274/0x3d0 <- vfs_open) mode=0xa800d inode=0xffff888004ada8d8
+
+You can see the `file::f_mode` and `file::f_inode` are upated in `vfs_open()`.
diff --git a/Documentation/trace/kprobetrace.rst b/Documentation/trace/kprobetrace.rst
index bf9cecb69fc9..a49662ccd53c 100644
--- a/Documentation/trace/kprobetrace.rst
+++ b/Documentation/trace/kprobetrace.rst
@@ -70,6 +70,15 @@ Synopsis of kprobe_events
   (\*3) this is useful for fetching a field of data structures.
   (\*4) "u" means user-space dereference. See :ref:`user_mem_access`.
 
+Function arguments at kretprobe
+-------------------------------
+Function arguments can be accessed at kretprobe using $arg<N> fetcharg. This
+is useful to record the function parameter and return value at once, and
+trace the difference of structure fields (for debuging a function whether it
+correctly updates the given data structure or not).
+See the :ref:`sample<fprobetrace_exit_args_sample>` in fprobe event for how
+it works.
+
 .. _kprobetrace_types:
 
 Types