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Subject[PATCH 3/8] coresight: etm3x: Adding missing features of Coresight PTM components
Date
From: Muhammad Abdul WAHAB <muhammadabdul.wahab@centralesupelec.fr>

In the current driver for Coresight components, two features of PTM
components are missing:

1. Branch Broadcasting (present also in ETM but called Branch Output)
2. Return Stack (only present in PTM v1.0 and PTMv1.1)

These features can be added simply to the code using `mode` field of
`etm_config` struct.

1. **Branch Broadcast** : The branch broadcast feature is present in ETM
components as well and is called Branch output. It allows to retrieve
addresses for direct branch addresses alongside the indirect branch
addresses. For example, it could be useful in cases when tracing without
source code.
2. **Return Stack** : The return stack option allows to retrieve the
return addresses of function calls. It can be useful to avoid CRA
(Code Reuse Attacks) by keeping a shadowstack.

Signed-off-by: Muhammad Abdul Wahab <muhammadabdul.wahab@centralesupelec.fr>
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
---
drivers/hwtracing/coresight/coresight-etm.h | 5 +++++
drivers/hwtracing/coresight/coresight-etm3x-sysfs.c | 10 ++++++++++
2 files changed, 15 insertions(+)

diff --git a/drivers/hwtracing/coresight/coresight-etm.h b/drivers/hwtracing/coresight/coresight-etm.h
index 4a18ee499965..ad063d7444e1 100644
--- a/drivers/hwtracing/coresight/coresight-etm.h
+++ b/drivers/hwtracing/coresight/coresight-etm.h
@@ -89,11 +89,13 @@
/* ETMCR - 0x00 */
#define ETMCR_PWD_DWN BIT(0)
#define ETMCR_STALL_MODE BIT(7)
+#define ETMCR_BRANCH_BROADCAST BIT(8)
#define ETMCR_ETM_PRG BIT(10)
#define ETMCR_ETM_EN BIT(11)
#define ETMCR_CYC_ACC BIT(12)
#define ETMCR_CTXID_SIZE (BIT(14)|BIT(15))
#define ETMCR_TIMESTAMP_EN BIT(28)
+#define ETMCR_RETURN_STACK BIT(29)
/* ETMCCR - 0x04 */
#define ETMCCR_FIFOFULL BIT(23)
/* ETMPDCR - 0x310 */
@@ -110,8 +112,11 @@
#define ETM_MODE_STALL BIT(2)
#define ETM_MODE_TIMESTAMP BIT(3)
#define ETM_MODE_CTXID BIT(4)
+#define ETM_MODE_BBROAD BIT(5)
+#define ETM_MODE_RET_STACK BIT(6)
#define ETM_MODE_ALL (ETM_MODE_EXCLUDE | ETM_MODE_CYCACC | \
ETM_MODE_STALL | ETM_MODE_TIMESTAMP | \
+ ETM_MODE_BBROAD | ETM_MODE_RET_STACK | \
ETM_MODE_CTXID | ETM_MODE_EXCL_KERN | \
ETM_MODE_EXCL_USER)

diff --git a/drivers/hwtracing/coresight/coresight-etm3x-sysfs.c b/drivers/hwtracing/coresight/coresight-etm3x-sysfs.c
index 5ea090955c08..ca98ad13bb8c 100644
--- a/drivers/hwtracing/coresight/coresight-etm3x-sysfs.c
+++ b/drivers/hwtracing/coresight/coresight-etm3x-sysfs.c
@@ -164,6 +164,16 @@ static ssize_t mode_store(struct device *dev,
else
config->ctrl &= ~ETMCR_CTXID_SIZE;

+ if (config->mode & ETM_MODE_BBROAD)
+ config->ctrl |= ETMCR_BRANCH_BROADCAST;
+ else
+ config->ctrl &= ~ETMCR_BRANCH_BROADCAST;
+
+ if (config->mode & ETM_MODE_RET_STACK)
+ config->ctrl |= ETMCR_RETURN_STACK;
+ else
+ config->ctrl &= ~ETMCR_RETURN_STACK;
+
if (config->mode & (ETM_MODE_EXCL_KERN | ETM_MODE_EXCL_USER))
etm_config_trace_mode(config);

--
2.7.4
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