linux-kernel - [PATCH] perf probe: support signedness casting

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Date:	Fri, 5 Aug 2016 14:33:53 +0900
From:	Naohiro Aota <naohiro.aota@...t.com>
To:	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Masami Hiramatsu <mhiramat@...nel.org>
CC:	Wang Nan <wangnan0@...wei.com>,
	Hemant Kumar <hemant@...ux.vnet.ibm.com>,
	<linux-kernel@...r.kernel.org>,
	Naohiro Aota <naohiro.aota@...t.com>
Subject: [PATCH] perf probe: support signedness casting

Perf-probe detects a variable's type and use the detected type to add new
probe. Then, kprobes prints its variable in hexadecimal format if the
variable is unsigned and prints in decimal if it is signed.

We sometimes want to see unsigned variable in decimal format (e.g.
sector_t or size_t). In that case, we need to investigate variable's
size manually to specify just signedness.

This patch add signedness casting support. By specifying "s" or "u" as a
type, perf-probe will investigate variable size as usual and use
the specified signedness.

Signed-off-by: Naohiro Aota <naohiro.aota@...t.com>
---
 tools/perf/util/probe-finder.c | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/tools/perf/util/probe-finder.c b/tools/perf/util/probe-finder.c
index f2d9ff0..5c290c6 100644
--- a/tools/perf/util/probe-finder.c
+++ b/tools/perf/util/probe-finder.c
@@ -297,10 +297,13 @@ static int convert_variable_type(Dwarf_Die *vr_die,
 	char sbuf[STRERR_BUFSIZE];
 	int bsize, boffs, total;
 	int ret;
+	char sign;

 	/* TODO: check all types */
-	if (cast && strcmp(cast, "string") != 0) {
+	if (cast && strcmp(cast, "string") != 0 &&
+	    strcmp(cast, "s") != 0 && strcmp(cast, "u") != 0) {
 		/* Non string type is OK */
+		/* and respect signedness cast */
 		tvar->type = strdup(cast);
 		return (tvar->type == NULL) ? -ENOMEM : 0;
 	}
@@ -361,6 +364,13 @@ static int convert_variable_type(Dwarf_Die *vr_die,
 		return (tvar->type == NULL) ? -ENOMEM : 0;
 	}

+	if (cast && (strcmp(cast, "u") == 0))
+		sign = 'u';
+	else if (cast && (strcmp(cast, "s") == 0))
+		sign = 's';
+	else
+		sign = die_is_signed_type(&type) ? 's' : 'u';
+
 	ret = dwarf_bytesize(&type);
 	if (ret <= 0)
 		/* No size ... try to use default type */
@@ -373,8 +383,7 @@ static int convert_variable_type(Dwarf_Die *vr_die,
 			dwarf_diename(&type), MAX_BASIC_TYPE_BITS);
 		ret = MAX_BASIC_TYPE_BITS;
 	}
-	ret = snprintf(buf, 16, "%c%d",
-		       die_is_signed_type(&type) ? 's' : 'u', ret);
+	ret = snprintf(buf, 16, "%c%d", sign, ret);

 formatted:
 	if (ret < 0 || ret >= 16) {
-- 
2.7.3

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