linux-kernel - [PATCH] tracing: Remove pointer (asterisk) from cpumask

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Date:   Mon, 12 Dec 2022 13:03:52 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     LKML <linux-kernel@...r.kernel.org>,
        Linux Trace Kernel <linux-trace-kernel@...r.kernel.org>
Cc:     Masami Hiramatsu <mhiramat@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Douglas Raillard <douglas.raillard@....com>,
        Valentin Schneider <vschneid@...hat.com>
Subject: [PATCH] tracing: Remove pointer (asterisk) from cpumask_t field

From: "Steven Rostedt (Google)" <rostedt@...dmis.org>

To differentiate between long arrays and cpumasks, the __cpumask() field
was created. Part of the TRACE_EVENT() macros test if the type is signed
or not by using the is_signed_type() macro. The __cpumask() field used the
__dynamic_array() helper but because cpumask_t is a structure, it could
not be used in the is_signed_type() macro as that would fail to build, so
instead it passed in the pointer to cpumask_t.

Unfortunately, that creates in the format file:

  field:__data_loc cpumask_t *[] mask;    offset:36;      size:4; signed:0;

Which looks like an array of pointers to cpumask_t and not a cpumask_t
type, which is misleading to user space parsers.

Instead, create another helper called __dynamic_array_sign() that can be
used directly by the __cpumaks() field macro where it passes in an
unsigned value to avoid using the is_signed_type() and have the
__dynamic_array() macro call it by passing it the is_signed_type() on the
type.

This now produces:

  field:__data_loc cpumask_t[] mask;    offset:36;      size:4; signed:0;

Which is the correct type of the field.

Link: https://lore.kernel.org/lkml/6dda5e1d-9416-b55e-88f3-31d148bc925f@arm.com/

Fixes: 8230f27b1ccc ("tracing: Add __cpumask to denote a trace event field that is a cpumask_t")
Reported-by: Douglas Raillard <douglas.raillard@....com>
Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.org>
---
 include/trace/stages/stage4_event_fields.h | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/include/trace/stages/stage4_event_fields.h b/include/trace/stages/stage4_event_fields.h
index f2990d22313c..9f0049c309f0 100644
--- a/include/trace/stages/stage4_event_fields.h
+++ b/include/trace/stages/stage4_event_fields.h
@@ -28,11 +28,15 @@
 	.size = sizeof(_type[_len]), .align = ALIGN_STRUCTFIELD(_type),	\
 	.is_signed = is_signed_type(_type), .filter_type = FILTER_OTHER },
 
-#undef __dynamic_array
-#define __dynamic_array(_type, _item, _len) {				\
+#undef __dynamic_array_sign
+#define __dynamic_array_sign(_type, _item, _len, _sign) {		\
 	.type = "__data_loc " #_type "[]", .name = #_item,		\
 	.size = 4, .align = 4,						\
-	.is_signed = is_signed_type(_type), .filter_type = FILTER_OTHER },
+	.is_signed = _sign, .filter_type = FILTER_OTHER },
+
+#undef __dynamic_array
+#define __dynamic_array(_type, _item, _len)				\
+	__dynamic_array_sign(_type, item, len, is_signed_type(_type))
 
 #undef __string
 #define __string(item, src) __dynamic_array(char, item, -1)
@@ -47,7 +51,7 @@
 #define __bitmask(item, nr_bits) __dynamic_array(unsigned long, item, -1)
 
 #undef __cpumask
-#define __cpumask(item) __dynamic_array(cpumask_t *, item, -1)
+#define __cpumask(item) __dynamic_array_sign(cpumask_t, item, -1, 0)
 
 #undef __sockaddr
 #define __sockaddr(field, len) __dynamic_array(u8, field, len)
-- 
2.35.1