Hi Mathieu,

On Tue, Sep 03, 2019 at 04:22:15PM -0600, Mathieu Poirier wrote:

On Fri, Aug 30, 2019 at 02:24:19PM +0800, Leo Yan wrote:

quoted

There has several code pieces need to know the instruction size, but
now every place calculates the instruction size separately.

This patch refactors to create a new function cs_etm__instr_size() as
a central place to analyze the instruction length based on ISA type
and instruction value.

Signed-off-by: Leo Yan <redacted>
---
 tools/perf/util/cs-etm.c | 44 +++++++++++++++++++++++++++-------------
 1 file changed, 30 insertions(+), 14 deletions(-)

diff --git a/tools/perf/util/cs-etm.c b/tools/perf/util/cs-etm.c
index b3a5daaf1a8f..882a0718033d 100644
--- a/tools/perf/util/cs-etm.c
+++ b/tools/perf/util/cs-etm.c

@@ -914,6 +914,26 @@ static inline int cs_etm__t32_instr_size(struct cs_etm_queue *etmq,
 	return ((instrBytes[1] & 0xF8) >= 0xE8) ? 4 : 2;
 }
 
+static inline int cs_etm__instr_size(struct cs_etm_queue *etmq,
+				     u8 trace_chan_id,
+				     enum cs_etm_isa isa,
+				     u64 addr)
+{
+	int insn_len;
+
+	/*
+	 * T32 instruction size might be 32-bit or 16-bit, decide by calling
+	 * cs_etm__t32_instr_size().
+	 */
+	if (isa == CS_ETM_ISA_T32)
+		insn_len = cs_etm__t32_instr_size(etmq, trace_chan_id, addr);
+	/* Otherwise, A64 and A32 instruction size are always 32-bit. */
+	else
+		insn_len = 4;
+
+	return insn_len;
+}
+
 static inline u64 cs_etm__first_executed_instr(struct cs_etm_packet *packet)
 {
 	/* Returns 0 for the CS_ETM_DISCONTINUITY packet */

@@ -938,19 +958,23 @@ static inline u64 cs_etm__instr_addr(struct cs_etm_queue *etmq,
 				     const struct cs_etm_packet *packet,
 				     u64 offset)
 {
+	int insn_len;
+
 	if (packet->isa == CS_ETM_ISA_T32) {
 		u64 addr = packet->start_addr;
 
 		while (offset > 0) {
-			addr += cs_etm__t32_instr_size(etmq,
-						       trace_chan_id, addr);
+			addr += cs_etm__instr_size(etmq, trace_chan_id,
+						   packet->isa, addr);
 			offset--;
 		}
 		return addr;
 	}
 
-	/* Assume a 4 byte instruction size (A32/A64) */
-	return packet->start_addr + offset * 4;
+	/* Return instruction size for A32/A64 */
+	insn_len = cs_etm__instr_size(etmq, trace_chan_id,
+				      packet->isa, packet->start_addr);
+	return packet->start_addr + offset * insn_len;

This patch will work but from where I stand it makes things difficult to
understand more than anything else.  It is also adding coupling between function
cs_etm__instr_addr() and cs_etm__instr_size(), meaning the code needs to be
carefully inspected in order to make changes to either one.

My purpose is to use a same place to calculate the instruction
size, rather than to spread the duplicate codes in several different
functions.

Last but not least function cs_etm__instr_size() isn't used in the upcoming
patches.  I really don't see what is gained here. 

Sorry that I forgot to commit my final change into patch 02.

I planed to use cs_etm__instr_size() in patch 02; patch 02 has
function cs_etm__add_stack_event(), which also needs to get the
instruction size when it sends stack event.

After apply patch 02, tools/perf/util/cs-etm.c will have below three
functions to caculate instruction size; this is the main reason I want
to refactor the code for instruction size.

  cs_etm__instr_addr()
  cs_etm__copy_insn()
  cs_etm__add_stack_event()

If this lets code more difficult to understand, will drop it.

Thanks,
Leo Yan

quoted

 }
 
 static void cs_etm__update_last_branch_rb(struct cs_etm_queue *etmq,

@@ -1090,16 +1114,8 @@ static void cs_etm__copy_insn(struct cs_etm_queue *etmq,
 		return;
 	}
 
-	/*
-	 * T32 instruction size might be 32-bit or 16-bit, decide by calling
-	 * cs_etm__t32_instr_size().
-	 */
-	if (packet->isa == CS_ETM_ISA_T32)
-		sample->insn_len = cs_etm__t32_instr_size(etmq, trace_chan_id,
-							  sample->ip);
-	/* Otherwise, A64 and A32 instruction size are always 32-bit. */
-	else
-		sample->insn_len = 4;
+	sample->insn_len = cs_etm__instr_size(etmq, trace_chan_id,
+					      packet->isa, sample->ip);
 
 	cs_etm__mem_access(etmq, trace_chan_id, sample->ip,
 			   sample->insn_len, (void *)sample->insn);

-- 
2.17.1

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