Re: [PATCH v6 06/21] perf arm-spe: Refactor printing string to buffer

From: André Przywara
Date: Mon Nov 02 2020 - 10:51:08 EST

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On 30/10/2020 02:57, 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
> it's used by the caller arm_spe_pkt_desc(); if printing buffer is called
> for multiple times in a flow, the error is a cumulative value and simply
> returns its final 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@xxxxxxx>
> Signed-off-by: Leo Yan <leo.yan@xxxxxxxxxx>

Wow, that's a bit tricky to review in its current incarnation, but it
looks alright to me.
I have some optimisation idea below, but that's a nit and the patch as
is seems correct to me (checked twice, the second time in an editor,
matching the lines), so:

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

...

> ---
> .../arm-spe-decoder/arm-spe-pkt-decoder.c | 267 ++++++++----------
> 1 file changed, 117 insertions(+), 150 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..1ecaf9805b79 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 +259,158 @@ int arm_spe_get_packet(const unsigned char *buf, size_t len,
> return ret;
> }
>
> +static int arm_spe_pkt_snprintf(int *err, char **buf_p, size_t *blen,
> + const char *fmt, ...)
> +{
> + va_list ap;
> + int ret;
> +
> + /* Bail out if any error occurred */
> + if (err && *err)
> + return *err;
> +
> + va_start(ap, fmt);
> + ret = vsnprintf(*buf_p, *blen, fmt, ap);
> + va_end(ap);
> +
> + if (ret < 0) {
> + if (err && !*err)
> + *err = ret;
> + } else {
> + *buf_p += ret;
> + *blen -= ret;
> + }
> +
> + return ret;
> +}
> +
> 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);
> + size_t blen = buf_len;
> + int err = 0;
>
> 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;
> - if (payload & 0x1) {
> - ret = snprintf(buf, buf_len, " EXCEPTION-GEN");
> - buf += ret;
> - blen -= ret;
> - }
> - if (payload & 0x2) {
> - ret = snprintf(buf, buf_len, " RETIRED");
> - buf += ret;
> - blen -= ret;
> - }
> - if (payload & 0x4) {
> - ret = snprintf(buf, buf_len, " L1D-ACCESS");
> - buf += ret;
> - blen -= ret;
> - }
> - if (payload & 0x8) {
> - ret = snprintf(buf, buf_len, " L1D-REFILL");
> - buf += ret;
> - blen -= ret;
> - }
> - if (payload & 0x10) {
> - ret = snprintf(buf, buf_len, " TLB-ACCESS");
> - buf += ret;
> - blen -= ret;
> - }
> - if (payload & 0x20) {
> - ret = snprintf(buf, buf_len, " TLB-REFILL");
> - buf += ret;
> - blen -= ret;
> - }
> - if (payload & 0x40) {
> - ret = snprintf(buf, buf_len, " NOT-TAKEN");
> - buf += ret;
> - blen -= ret;
> - }
> - if (payload & 0x80) {
> - ret = snprintf(buf, buf_len, " MISPRED");
> - buf += ret;
> - blen -= ret;
> - }
> + return arm_spe_pkt_snprintf(&err, &buf, &blen, "%s", name);

Nothing critical, but in case you need to respin this series for
whatever reason, you might want to use NULL for the first argument,
since you return here and there is little point in setting err. Same for
other cases where you return directly from an arm_spe_pkt_snprintf() call.
But it doesn't hurt, so you could leave it as well, and it's more robust
in case someone extends the code later.

> + case ARM_SPE_EVENTS:
> + arm_spe_pkt_snprintf(&err, &buf, &blen, "EV");
> +
> + if (payload & 0x1)
> + arm_spe_pkt_snprintf(&err, &buf, &blen, " EXCEPTION-GEN");
> + if (payload & 0x2)
> + arm_spe_pkt_snprintf(&err, &buf, &blen, " RETIRED");
> + if (payload & 0x4)
> + arm_spe_pkt_snprintf(&err, &buf, &blen, " L1D-ACCESS");
> + if (payload & 0x8)
> + arm_spe_pkt_snprintf(&err, &buf, &blen, " L1D-REFILL");
> + if (payload & 0x10)
> + arm_spe_pkt_snprintf(&err, &buf, &blen, " TLB-ACCESS");
> + if (payload & 0x20)
> + arm_spe_pkt_snprintf(&err, &buf, &blen, " TLB-REFILL");
> + if (payload & 0x40)
> + arm_spe_pkt_snprintf(&err, &buf, &blen, " NOT-TAKEN");
> + if (payload & 0x80)
> + arm_spe_pkt_snprintf(&err, &buf, &blen, " MISPRED");
> if (idx > 1) {
> - if (payload & 0x100) {
> - ret = snprintf(buf, buf_len, " LLC-ACCESS");
> - buf += ret;
> - blen -= ret;
> - }
> - if (payload & 0x200) {
> - ret = snprintf(buf, buf_len, " LLC-REFILL");
> - buf += ret;
> - blen -= ret;
> - }
> - if (payload & 0x400) {
> - ret = snprintf(buf, buf_len, " REMOTE-ACCESS");
> - buf += ret;
> - blen -= ret;
> - }
> + if (payload & 0x100)
> + arm_spe_pkt_snprintf(&err, &buf, &blen, " LLC-ACCESS");
> + if (payload & 0x200)
> + arm_spe_pkt_snprintf(&err, &buf, &blen, " LLC-REFILL");
> + if (payload & 0x400)
> + arm_spe_pkt_snprintf(&err, &buf, &blen, " REMOTE-ACCESS");
> }
> - if (ret < 0)
> - return ret;
> - blen -= ret;
> - return buf_len - blen;
> - }
> + return err ?: (int)(buf_len - blen);
> +
> case ARM_SPE_OP_TYPE:
> switch (idx) {
> - case 0: return snprintf(buf, buf_len, "%s", payload & 0x1 ?
> - "COND-SELECT" : "INSN-OTHER");
> - case 1: {
> - size_t blen = buf_len;
> + case 0:
> + return arm_spe_pkt_snprintf(&err, &buf, &blen,
> + payload & 0x1 ? "COND-SELECT" : "INSN-OTHER");

same here (and below, you get the idea ...)

Cheers,
Andre

> + case 1:
> + arm_spe_pkt_snprintf(&err, &buf, &blen,
> + payload & 0x1 ? "ST" : "LD");
>
> - if (payload & 0x1)
> - ret = snprintf(buf, buf_len, "ST");
> - else
> - ret = snprintf(buf, buf_len, "LD");
> - buf += ret;
> - blen -= ret;
> if (payload & 0x2) {
> - if (payload & 0x4) {
> - ret = snprintf(buf, buf_len, " AT");
> - buf += ret;
> - blen -= ret;
> - }
> - if (payload & 0x8) {
> - ret = snprintf(buf, buf_len, " EXCL");
> - buf += ret;
> - blen -= ret;
> - }
> - if (payload & 0x10) {
> - ret = snprintf(buf, buf_len, " AR");
> - buf += ret;
> - blen -= ret;
> - }
> + if (payload & 0x4)
> + arm_spe_pkt_snprintf(&err, &buf, &blen, " AT");
> + if (payload & 0x8)
> + arm_spe_pkt_snprintf(&err, &buf, &blen, " EXCL");
> + if (payload & 0x10)
> + arm_spe_pkt_snprintf(&err, &buf, &blen, " AR");
> } else if (payload & 0x4) {
> - ret = snprintf(buf, buf_len, " SIMD-FP");
> - buf += ret;
> - blen -= ret;
> - }
> - if (ret < 0)
> - return ret;
> - blen -= ret;
> - return buf_len - blen;
> - }
> - case 2: {
> - size_t blen = buf_len;
> -
> - ret = snprintf(buf, buf_len, "B");
> - buf += ret;
> - blen -= ret;
> - if (payload & 0x1) {
> - ret = snprintf(buf, buf_len, " COND");
> - buf += ret;
> - blen -= ret;
> - }
> - if (payload & 0x2) {
> - ret = snprintf(buf, buf_len, " IND");
> - buf += ret;
> - blen -= ret;
> + arm_spe_pkt_snprintf(&err, &buf, &blen, " SIMD-FP");
> }
> - if (ret < 0)
> - return ret;
> - blen -= ret;
> - return buf_len - blen;
> - }
> - default: return 0;
> +
> + return err ?: (int)(buf_len - blen);
> +
> + case 2:
> + arm_spe_pkt_snprintf(&err, &buf, &blen, "B");
> +
> + if (payload & 0x1)
> + arm_spe_pkt_snprintf(&err, &buf, &blen, " COND");
> + if (payload & 0x2)
> + arm_spe_pkt_snprintf(&err, &buf, &blen, " IND");
> +
> + return err ?: (int)(buf_len - blen);
> +
> + default:
> + return 0;
> }
> case ARM_SPE_DATA_SOURCE:
> case ARM_SPE_TIMESTAMP:
> - return snprintf(buf, buf_len, "%s %lld", name, payload);
> + return arm_spe_pkt_snprintf(&err, &buf, &blen, "%s %lld", name, payload);
> case ARM_SPE_ADDRESS:
> switch (idx) {
> case 0:
> case 1: ns = !!(packet->payload & NS_FLAG);
> el = (packet->payload & EL_FLAG) >> 61;
> payload &= ~(0xffULL << 56);
> - return snprintf(buf, buf_len, "%s 0x%llx el%d ns=%d",
> + return arm_spe_pkt_snprintf(&err, &buf, &blen,
> + "%s 0x%llx el%d ns=%d",
> (idx == 1) ? "TGT" : "PC", payload, el, ns);
> - case 2: return snprintf(buf, buf_len, "VA 0x%llx", payload);
> + case 2:
> + return arm_spe_pkt_snprintf(&err, &buf, &blen,
> + "VA 0x%llx", payload);
> case 3: ns = !!(packet->payload & NS_FLAG);
> payload &= ~(0xffULL << 56);
> - return snprintf(buf, buf_len, "PA 0x%llx ns=%d",
> - payload, ns);
> - default: return 0;
> + return arm_spe_pkt_snprintf(&err, &buf, &blen,
> + "PA 0x%llx ns=%d", payload, ns);
> + default:
> + return 0;
> }
> case ARM_SPE_CONTEXT:
> - return snprintf(buf, buf_len, "%s 0x%lx el%d", name,
> - (unsigned long)payload, idx + 1);
> - case ARM_SPE_COUNTER: {
> - size_t blen = buf_len;
> -
> - ret = snprintf(buf, buf_len, "%s %d ", name,
> - (unsigned short)payload);
> - buf += ret;
> - blen -= ret;
> + return arm_spe_pkt_snprintf(&err, &buf, &blen, "%s 0x%lx el%d",
> + name, (unsigned long)payload, idx + 1);
> + case ARM_SPE_COUNTER:
> + arm_spe_pkt_snprintf(&err, &buf, &blen, "%s %d ", name,
> + (unsigned short)payload);
> +
> switch (idx) {
> - case 0: ret = snprintf(buf, buf_len, "TOT"); break;
> - case 1: ret = snprintf(buf, buf_len, "ISSUE"); break;
> - case 2: ret = snprintf(buf, buf_len, "XLAT"); break;
> - default: ret = 0;
> + case 0:
> + arm_spe_pkt_snprintf(&err, &buf, &blen, "TOT");
> + break;
> + case 1:
> + arm_spe_pkt_snprintf(&err, &buf, &blen, "ISSUE");
> + break;
> + case 2:
> + arm_spe_pkt_snprintf(&err, &buf, &blen, "XLAT");
> + break;
> + default:
> + break;
> }
> - if (ret < 0)
> - return ret;
> - blen -= ret;
> - return buf_len - blen;
> - }
> +
> + return err ?: (int)(buf_len - blen);
> +
> default:
> break;
> }
>
> - return snprintf(buf, buf_len, "%s 0x%llx (%d)",
> - name, payload, packet->index);
> + return arm_spe_pkt_snprintf(&err, &buf, &blen, "%s 0x%llx (%d)",
> + name, payload, packet->index);
> }
>

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