Messages in this thread Patch in this message | | | Date | Tue, 27 Oct 2020 14:31:54 +0000 | From | Dave Martin <> | Subject | Re: [PATCH v4 06/21] perf arm-spe: Refactor printing string to buffer |
| |
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.
[...]
Cheers ---Dave
| |