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SubjectRe: [PATCH v1 1/3] perf cs-etm: Refactor instruction size handling
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:
> > 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 <leo.yan@linaro.org>
> > ---
> > 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

> > }
> >
> > 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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