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.mar...@arm.com>
> > Signed-off-by: Leo Yan <leo....@linaro.org>
> > Reviewed-by: Andre Przywara <andre.przyw...@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
