linux-kernel - [PATCH] perf script python: Fix buffer size to report iregs in perf script

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Date:   Mon, 28 Jun 2021 11:53:41 +0530
From:   Kajol Jain <kjain@...ux.ibm.com>
To:     acme@...nel.org
Cc:     maddy@...ux.vnet.ibm.com, atrajeev@...ux.vnet.ibm.com,
        kjain@...ux.ibm.com, pc@...ibm.com, linux-kernel@...r.kernel.org,
        jolsa@...hat.com, ravi.bangoria@...ux.ibm.com,
        linux-perf-users@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        rnsastry@...ux.ibm.com
Subject: [PATCH] perf script python: Fix buffer size to report iregs in perf script

Commit 48a1f565261d ("perf script python: Add more PMU fields
to event handler dict") added functionality to report fields like
weight, iregs, uregs etc via perf report.
That commit predefined buffer size to 512 bytes to print those fields.

But incase of powerpc, since we added extended regs support
in commits:

Commit 068aeea3773a ("perf powerpc: Support exposing Performance Monitor
Counter SPRs as part of extended regs")
Commit d735599a069f ("powerpc/perf: Add extended regs support for
power10 platform")

Now iregs can carry more bytes of data and this predefined buffer size
can result to data loss in perf script output.

Patch resolve this issue by making buffer size dynamic based on number
of registers needed to print. It also changed return type for function
"regs_map" from int to void, as the return value is not being used by
the caller function "set_regs_in_dict".

Fixes: 068aeea3773a ("perf powerpc: Support exposing Performance Monitor
Counter SPRs as part of extended regs")
Signed-off-by: Kajol Jain <kjain@...ux.ibm.com>
---
 .../util/scripting-engines/trace-event-python.c | 17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)

diff --git a/tools/perf/util/scripting-engines/trace-event-python.c b/tools/perf/util/scripting-engines/trace-event-python.c
index 4e4aa4c97ac5..c8c9706b4643 100644
--- a/tools/perf/util/scripting-engines/trace-event-python.c
+++ b/tools/perf/util/scripting-engines/trace-event-python.c
@@ -687,7 +687,7 @@ static void set_sample_datasrc_in_dict(PyObject *dict,
 			_PyUnicode_FromString(decode));
 }
 
-static int regs_map(struct regs_dump *regs, uint64_t mask, char *bf, int size)
+static void regs_map(struct regs_dump *regs, uint64_t mask, char *bf, int size)
 {
 	unsigned int i = 0, r;
 	int printed = 0;
@@ -695,7 +695,7 @@ static int regs_map(struct regs_dump *regs, uint64_t mask, char *bf, int size)
 	bf[0] = 0;
 
 	if (!regs || !regs->regs)
-		return 0;
+		return;
 
 	for_each_set_bit(r, (unsigned long *) &mask, sizeof(mask) * 8) {
 		u64 val = regs->regs[i++];
@@ -704,8 +704,6 @@ static int regs_map(struct regs_dump *regs, uint64_t mask, char *bf, int size)
 				     "%5s:0x%" PRIx64 " ",
 				     perf_reg_name(r), val);
 	}
-
-	return printed;
 }
 
 static void set_regs_in_dict(PyObject *dict,
@@ -713,7 +711,16 @@ static void set_regs_in_dict(PyObject *dict,
 			     struct evsel *evsel)
 {
 	struct perf_event_attr *attr = &evsel->core.attr;
-	char bf[512];
+
+	/*
+	 * Here value 28 is a constant size which can be used to print
+	 * one register value and its corresponds to:
+	 * 16 chars is to specify 64 bit register in hexadecimal.
+	 * 2 chars is for appending "0x" to the hexadecimal value and
+	 * 10 chars is for register name.
+	 */
+	int size = __sw_hweight64(attr->sample_regs_intr) * 28;
+	char bf[size];
 
 	regs_map(&sample->intr_regs, attr->sample_regs_intr, bf, sizeof(bf));
 
-- 
2.31.1