Messages in this thread Patch in this message | | | Date | Tue, 27 Oct 2020 22:50:38 +0800 | From | Leo Yan <> | Subject | Re: [PATCH v4 06/21] perf arm-spe: Refactor printing string to buffer |
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Hi Dave,
On Tue, Oct 27, 2020 at 02:31:54PM +0000, Dave Martin wrote: > On Tue, Oct 27, 2020 at 03:09:02AM +0000, Leo Yan wrote: > > When outputs strings to the decoding buffer with function snprintf(), > > SPE decoder needs to detects if any error returns from snprintf() and if > > so needs to directly bail out. If snprintf() returns success, it needs > > to update buffer pointer and reduce the buffer length so can continue to > > output the next string into the consequent memory space. > > > > This complex logics are spreading in the function arm_spe_pkt_desc() so > > there has many duplicate codes for handling error detecting, increment > > buffer pointer and decrement buffer size. > > > > To avoid the duplicate code, this patch introduces a new helper function > > arm_spe_pkt_snprintf() which is used to wrap up the complex logics, and > > the caller arm_spe_pkt_desc() will call it and simply check the returns > > value. > > > > This patch also moves the variable 'blen' as the function's local > > variable, this allows to remove the unnecessary braces and improve the > > readability. > > > > Suggested-by: Dave Martin <Dave.Martin@arm.com> > > Signed-off-by: Leo Yan <leo.yan@linaro.org> > > Reviewed-by: Andre Przywara <andre.przywara@arm.com> > > --- > > .../arm-spe-decoder/arm-spe-pkt-decoder.c | 247 ++++++++++-------- > > 1 file changed, 135 insertions(+), 112 deletions(-) > > > > diff --git a/tools/perf/util/arm-spe-decoder/arm-spe-pkt-decoder.c b/tools/perf/util/arm-spe-decoder/arm-spe-pkt-decoder.c > > index 04fd7fd7c15f..b400636e6da2 100644 > > --- a/tools/perf/util/arm-spe-decoder/arm-spe-pkt-decoder.c > > +++ b/tools/perf/util/arm-spe-decoder/arm-spe-pkt-decoder.c > > @@ -9,6 +9,7 @@ > > #include <endian.h> > > #include <byteswap.h> > > #include <linux/bitops.h> > > +#include <stdarg.h> > > > > #include "arm-spe-pkt-decoder.h" > > > > @@ -258,192 +259,214 @@ int arm_spe_get_packet(const unsigned char *buf, size_t len, > > return ret; > > } > > > > +static int arm_spe_pkt_snprintf(char **buf_p, size_t *blen, > > + const char *fmt, ...) > > +{ > > + va_list ap; > > + int ret; > > + > > + va_start(ap, fmt); > > + ret = vsnprintf(*buf_p, *blen, fmt, ap); > > + va_end(ap); > > + > > + if (ret < 0) > > + return ret; > > + > > + *buf_p += ret; > > + *blen -= ret; > > + return ret; > > +} > > + > > This approach seems OK, though I wonder whether all the > "if (ret < 0) return;" logic is really needed. > > In case of failure, it probably doesn't matter what ends up in buf. > If not, we could just implement a cumulative error: > > static int arm_spe_pkt_snprintf(int *err, char **buf_p, size_t *blen, > { > > /* ... */ > > if (ret < 0) { > if (err && !*err) > *err = ret; > } else { > *buf_p += ret; > *blen -= ret; > } > > return err ? *err : ret; > } > > and just return the final value of err. > > > > > int arm_spe_pkt_desc(const struct arm_spe_pkt *packet, char *buf, > > size_t buf_len) > > { > > int ret, ns, el, idx = packet->index; > > unsigned long long payload = packet->payload; > > const char *name = arm_spe_pkt_name(packet->type); > > + size_t blen = buf_len; > > > > switch (packet->type) { > > case ARM_SPE_BAD: > > case ARM_SPE_PAD: > > case ARM_SPE_END: > > - return snprintf(buf, buf_len, "%s", name); > > - case ARM_SPE_EVENTS: { > > - size_t blen = buf_len; > > - > > - ret = 0; > > - ret = snprintf(buf, buf_len, "EV"); > > - buf += ret; > > - blen -= ret; > > + return arm_spe_pkt_snprintf(&buf, &blen, "%s", name); > > + case ARM_SPE_EVENTS: > > + ret = arm_spe_pkt_snprintf(&buf, &blen, "EV"); > > + if (ret < 0) > > + return ret; > > + > > ... > > Then this becomes > > case ARM_SPE_END: > return arm_spe_pkt_snprintf(&err, &buf, &blen, "%s", name); > case ARM_SPE_EVENTS: > arm_spe_pkt_snprintf(&ret, &buf, &blen, "%s", name); > > if (payload & 0x1) > arm_spe_pkt_snprintf(&err, &buf, &blen, " EXCEPTION-GEN"); > if (payload & 0x2) > arm_spe_pkt_snprintf(&err, &buf, &blen, " RETIRED"); > > /* ... */ > > > This might be over-engineering, but it does help to condense the code.
I agree this approach is more neat; will follow it to refine code.
Thanks a lot for detailed explaination.
Leo
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