Re: [PATCH v7 07/22] perf arm-spe: Consolidate arm_spe_pkt_desc()'s return value

From: André Przywara
Date: Mon Nov 09 2020 - 11:52:43 EST

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On 06/11/2020 01:41, Leo Yan wrote:
> arm_spe_pkt_desc() returns the length of consumed the buffer for
> the success case; otherwise, it delivers the return value from
> arm_spe_pkt_snprintf(), and returns the last return value if there have
> multiple calling arm_spe_pkt_snprintf().
>
> Since arm_spe_pkt_snprintf() has the same semantics with vsnprintf() for
> the return value, and vsnprintf() might return value equals to or bigger
> than the parameter 'size' to indicate the truncation. Because the
> return value is >= 0 when the string is truncated, this condition will
> be returned up the stack as "success".
>
> This patch simplifies the return value for arm_spe_pkt_desc(): '0' means
> success and other values mean an error has occurred. To realize this,
> it relies on arm_spe_pkt_snprintf()'s parameter 'err', the 'err' is a
> cumulative value, returns its final value if printing buffer is called
> for one time or multiple times.
>
> To unify the error value generation, this patch handles error in a
> central place, rather than directly bailing out in switch-cases,
> it returns error at the end of arm_spe_pkt_desc().

And the but-last hunk means it will basically always return 0?
Just checking, it's probably fine (and I don't want to review a v8 ;-)

> This patch changes the caller arm_spe_dump() to respect the updated
> return value semantics of arm_spe_pkt_desc().
>
> Suggested-by: Dave Martin <Dave.Martin@xxxxxxx>
> Signed-off-by: Leo Yan <leo.yan@xxxxxxxxxx>

One tiny thing below ...

> ---
> .../arm-spe-decoder/arm-spe-pkt-decoder.c | 128 +++++++++---------
> tools/perf/util/arm-spe.c | 2 +-
> 2 files changed, 68 insertions(+), 62 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 1970686f7020..33baef0c2c0b 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
> @@ -301,9 +301,10 @@ static int arm_spe_pkt_snprintf(int *err, char **buf_p, size_t *blen,
> int arm_spe_pkt_desc(const struct arm_spe_pkt *packet, char *buf,
> size_t buf_len)
> {
> - int ret, ns, el, idx = packet->index;
> + int ns, el, idx = packet->index;
> unsigned long long payload = packet->payload;
> const char *name = arm_spe_pkt_name(packet->type);
> + char *buf_orig = buf;
> size_t blen = buf_len;
> int err = 0;
>
> @@ -311,82 +312,76 @@ int arm_spe_pkt_desc(const struct arm_spe_pkt *packet, char *buf,
> case ARM_SPE_BAD:
> case ARM_SPE_PAD:
> case ARM_SPE_END:
> - return arm_spe_pkt_snprintf(&err, &buf, &blen, "%s", name);
> + arm_spe_pkt_snprintf(&err, &buf, &blen, "%s", name);
> + break;
> case ARM_SPE_EVENTS:
> - ret = arm_spe_pkt_snprintf(&err, &buf, &blen, "EV");
> + arm_spe_pkt_snprintf(&err, &buf, &blen, "EV");
>
> if (payload & 0x1)
> - ret = arm_spe_pkt_snprintf(&err, &buf, &blen, " EXCEPTION-GEN");
> + arm_spe_pkt_snprintf(&err, &buf, &blen, " EXCEPTION-GEN");
> if (payload & 0x2)
> - ret = arm_spe_pkt_snprintf(&err, &buf, &blen, " RETIRED");
> + arm_spe_pkt_snprintf(&err, &buf, &blen, " RETIRED");
> if (payload & 0x4)
> - ret = arm_spe_pkt_snprintf(&err, &buf, &blen, " L1D-ACCESS");
> + arm_spe_pkt_snprintf(&err, &buf, &blen, " L1D-ACCESS");
> if (payload & 0x8)
> - ret = arm_spe_pkt_snprintf(&err, &buf, &blen, " L1D-REFILL");
> + arm_spe_pkt_snprintf(&err, &buf, &blen, " L1D-REFILL");
> if (payload & 0x10)
> - ret = arm_spe_pkt_snprintf(&err, &buf, &blen, " TLB-ACCESS");
> + arm_spe_pkt_snprintf(&err, &buf, &blen, " TLB-ACCESS");
> if (payload & 0x20)
> - ret = arm_spe_pkt_snprintf(&err, &buf, &blen, " TLB-REFILL");
> + arm_spe_pkt_snprintf(&err, &buf, &blen, " TLB-REFILL");
> if (payload & 0x40)
> - ret = arm_spe_pkt_snprintf(&err, &buf, &blen, " NOT-TAKEN");
> + arm_spe_pkt_snprintf(&err, &buf, &blen, " NOT-TAKEN");
> if (payload & 0x80)
> - ret = arm_spe_pkt_snprintf(&err, &buf, &blen, " MISPRED");
> + arm_spe_pkt_snprintf(&err, &buf, &blen, " MISPRED");
> if (idx > 1) {
> if (payload & 0x100)
> - ret = arm_spe_pkt_snprintf(&err, &buf, &blen, " LLC-ACCESS");
> + arm_spe_pkt_snprintf(&err, &buf, &blen, " LLC-ACCESS");
> if (payload & 0x200)
> - ret = arm_spe_pkt_snprintf(&err, &buf, &blen, " LLC-REFILL");
> + arm_spe_pkt_snprintf(&err, &buf, &blen, " LLC-REFILL");
> if (payload & 0x400)
> - ret = arm_spe_pkt_snprintf(&err, &buf, &blen, " REMOTE-ACCESS");
> + arm_spe_pkt_snprintf(&err, &buf, &blen, " REMOTE-ACCESS");
> }
> - if (ret < 0)
> - return ret;
> - blen -= ret;
> - return buf_len - blen;
> + break;
> case ARM_SPE_OP_TYPE:
> switch (idx) {
> case 0:
> - return arm_spe_pkt_snprintf(&err, &buf, &blen,
> + arm_spe_pkt_snprintf(&err, &buf, &blen,
> payload & 0x1 ? "COND-SELECT" : "INSN-OTHER");
> + break;
> case 1:
> - ret = arm_spe_pkt_snprintf(&err, &buf, &blen,
> - payload & 0x1 ? "ST" : "LD");
> + arm_spe_pkt_snprintf(&err, &buf, &blen,
> + payload & 0x1 ? "ST" : "LD");
>
> if (payload & 0x2) {
> if (payload & 0x4)
> - ret = arm_spe_pkt_snprintf(&err, &buf, &blen, " AT");
> + arm_spe_pkt_snprintf(&err, &buf, &blen, " AT");
> if (payload & 0x8)
> - ret = arm_spe_pkt_snprintf(&err, &buf, &blen, " EXCL");
> + arm_spe_pkt_snprintf(&err, &buf, &blen, " EXCL");
> if (payload & 0x10)
> - ret = arm_spe_pkt_snprintf(&err, &buf, &blen, " AR");
> + arm_spe_pkt_snprintf(&err, &buf, &blen, " AR");
> } else if (payload & 0x4) {
> - ret = arm_spe_pkt_snprintf(&err, &buf, &blen, " SIMD-FP");
> + arm_spe_pkt_snprintf(&err, &buf, &blen, " SIMD-FP");
> }
> -
> - if (ret < 0)
> - return ret;
> - blen -= ret;
> - return buf_len - blen;
> -
> + break;
> case 2:
> - ret = arm_spe_pkt_snprintf(&err, &buf, &blen, "B");
> + arm_spe_pkt_snprintf(&err, &buf, &blen, "B");
>
> if (payload & 0x1)
> - ret = arm_spe_pkt_snprintf(&err, &buf, &blen, " COND");
> + arm_spe_pkt_snprintf(&err, &buf, &blen, " COND");
> if (payload & 0x2)
> - ret = arm_spe_pkt_snprintf(&err, &buf, &blen, " IND");
> -
> - if (ret < 0)
> - return ret;
> - blen -= ret;
> - return buf_len - blen;
> + arm_spe_pkt_snprintf(&err, &buf, &blen, " IND");
>
> + break;
> default:
> - return 0;
> + /* Unknown index */
> + err = -1;
> + break;
> }
> + break;
> case ARM_SPE_DATA_SOURCE:
> case ARM_SPE_TIMESTAMP:
> - return arm_spe_pkt_snprintf(&err, &buf, &blen, "%s %lld", name, payload);
> + arm_spe_pkt_snprintf(&err, &buf, &blen, "%s %lld", name, payload);
> + break;
> case ARM_SPE_ADDRESS:
> switch (idx) {
> case 0:
> @@ -394,48 +389,59 @@ int arm_spe_pkt_desc(const struct arm_spe_pkt *packet, char *buf,
> ns = !!(packet->payload & NS_FLAG);
> el = (packet->payload & EL_FLAG) >> 61;
> payload &= ~(0xffULL << 56);
> - return arm_spe_pkt_snprintf(&err, &buf, &blen,
> + arm_spe_pkt_snprintf(&err, &buf, &blen,
> "%s 0x%llx el%d ns=%d",
> (idx == 1) ? "TGT" : "PC", payload, el, ns);
> + break;
> case 2:
> - return arm_spe_pkt_snprintf(&err, &buf, &blen,
> - "VA 0x%llx", payload);
> + arm_spe_pkt_snprintf(&err, &buf, &blen,
> + "VA 0x%llx", payload);
> + break;
> case 3:
> ns = !!(packet->payload & NS_FLAG);
> payload &= ~(0xffULL << 56);
> - return arm_spe_pkt_snprintf(&err, &buf, &blen,
> - "PA 0x%llx ns=%d", payload, ns);
> + arm_spe_pkt_snprintf(&err, &buf, &blen,
> + "PA 0x%llx ns=%d", payload, ns);
> + break;
> default:
> - return 0;
> + /* Unknown index */
> + err = -1;
> + break;
> }
> + break;
> case ARM_SPE_CONTEXT:
> - return arm_spe_pkt_snprintf(&err, &buf, &blen, "%s 0x%lx el%d",
> - name, (unsigned long)payload, idx + 1);
> + arm_spe_pkt_snprintf(&err, &buf, &blen, "%s 0x%lx el%d",
> + name, (unsigned long)payload, idx + 1);
> + break;
> case ARM_SPE_COUNTER:
> - ret = arm_spe_pkt_snprintf(&err, &buf, &blen, "%s %d ", name,
> - (unsigned short)payload);
> + arm_spe_pkt_snprintf(&err, &buf, &blen, "%s %d ", name,
> + (unsigned short)payload);
> switch (idx) {
> case 0:
> - ret = arm_spe_pkt_snprintf(&err, &buf, &blen, "TOT");
> + arm_spe_pkt_snprintf(&err, &buf, &blen, "TOT");
> break;
> case 1:
> - ret = arm_spe_pkt_snprintf(&err, &buf, &blen, "ISSUE");
> + arm_spe_pkt_snprintf(&err, &buf, &blen, "ISSUE");
> break;
> case 2:
> - ret = arm_spe_pkt_snprintf(&err, &buf, &blen, "XLAT");
> + arm_spe_pkt_snprintf(&err, &buf, &blen, "XLAT");
> break;
> default:
> - ret = 0;
> break;
> }
> - if (ret < 0)
> - return ret;
> - blen -= ret;
> - return buf_len - blen;
> + break;
> default:
> + /* Unknown index */
> + err = -1;
> break;
> }
>
> - return arm_spe_pkt_snprintf(&err, &buf, &blen, "%s 0x%llx (%d)",
> - name, payload, packet->index);
> + /* Output raw data if detect any error */
> + if (err) {
> + err = 0;
> + arm_spe_pkt_snprintf(&err, &buf_orig, &blen, "%s 0x%llx (%d)",

That needs to be &buf_len here, doesn't it?

With that fixed:

Reviewed-by: Andre Przywara <andre.przywara@xxxxxxx>

Cheers,
Andre

> + name, payload, packet->index);
> + }
> +
> + return err;
> }
> diff --git a/tools/perf/util/arm-spe.c b/tools/perf/util/arm-spe.c
> index 3882a5360ada..8901a1656a41 100644
> --- a/tools/perf/util/arm-spe.c
> +++ b/tools/perf/util/arm-spe.c
> @@ -113,7 +113,7 @@ static void arm_spe_dump(struct arm_spe *spe __maybe_unused,
> if (ret > 0) {
> ret = arm_spe_pkt_desc(&packet, desc,
> ARM_SPE_PKT_DESC_MAX);
> - if (ret > 0)
> + if (!ret)
> color_fprintf(stdout, color, " %s\n", desc);
> } else {
> color_fprintf(stdout, color, " Bad packet!\n");
>

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Next in thread: Leo Yan: "Re: [PATCH v7 07/22] perf arm-spe: Consolidate arm_spe_pkt_desc()'s return value"
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