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Subject: Re: [PATCH v8 06/22] perf arm-spe: Refactor printing string to buffer
To:     Arnaldo Carvalho de Melo <acme@kernel.org>,
        Leo Yan <leo.yan@linaro.org>
Cc:     Dave Martin <Dave.Martin@arm.com>,
        James Clark <james.clark@arm.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>,
        Mark Rutland <mark.rutland@arm.com>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Jiri Olsa <jolsa@redhat.com>,
        Namhyung Kim <namhyung@kernel.org>,
        Al Grant <Al.Grant@arm.com>, Wei Li <liwei391@huawei.com>,
        John Garry <john.garry@huawei.com>,
        Will Deacon <will@kernel.org>,
        Mathieu Poirier <mathieu.poirier@linaro.org>,
        linux-kernel@vger.kernel.org
References: <20201111071149.815-1-leo.yan@linaro.org>
 <20201111071149.815-7-leo.yan@linaro.org>
 <20201111153555.GG355344@kernel.org>
From:   =?UTF-8?Q?Andr=c3=a9_Przywara?= <andre.przywara@arm.com>
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Organization: ARM Ltd.
Message-ID: <a1ca3412-3815-e2a8-0334-f3059802df6a@arm.com>
Date:   Wed, 11 Nov 2020 15:45:23 +0000
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On 11/11/2020 15:35, Arnaldo Carvalho de Melo wrote:

Hi Arnaldo,

thanks for taking a look!

> Em Wed, Nov 11, 2020 at 03:11:33PM +0800, Leo Yan escreveu:
>> 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().
>>
>> 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     | 260 +++++++++---------
>>  1 file changed, 126 insertions(+), 134 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..1970686f7020 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 +259,183 @@ 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;
>> +
>> +	/*
>> +	 * A return value of (*blen - 1) or more means that the
>> +	 * output was truncated and the buffer is overrun.
>> +	 */
>> +	} else if (ret >= ((int)*blen - 1)) {
>> +		(*buf_p)[*blen - 1] = '\0';
>> +
>> +		/*
>> +		 * Set *err to 'ret' to avoid overflow if tries to
>> +		 * fill this buffer sequentially.
>> +		 */
>> +		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;
>>  	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);
>> +	case ARM_SPE_EVENTS:
>> +		ret = arm_spe_pkt_snprintf(&err, &buf, &blen, "EV");
>> +
>> +		if (payload & 0x1)
>> +			ret = arm_spe_pkt_snprintf(&err, &buf, &blen, " EXCEPTION-GEN");
> 
> Isn't this 'ret +=' ? Otherwise if any of these arm_spe_pkt_snprintf()
> calls are made the previous 'ret' value is simply discarded. Can you
> clarify this?

ret is the same as err. If err is negative (from previous calls), we
return that straight away, so it does nothing but propagating the error.
That redundancy gets cleaned up in the next patch.

This patch split is somewhat cumbersome, but was done to simplify review
(originally 06 and 07 were one patch). The combined patch made it hard
to match the individual changes. If you feel unsure about it, or you
feel it looks better, you could also merge both 06/22 and 07/22 into a
single patch.

Hope that helps.

Cheers,
Andre.


> 
> I applied all patches before this one.
> 
> - Arnaldo
> 
>> +		if (payload & 0x2)
>> +			ret = arm_spe_pkt_snprintf(&err, &buf, &blen, " RETIRED");
>> +		if (payload & 0x4)
>> +			ret = arm_spe_pkt_snprintf(&err, &buf, &blen, " L1D-ACCESS");
>> +		if (payload & 0x8)
>> +			ret = arm_spe_pkt_snprintf(&err, &buf, &blen, " L1D-REFILL");
>> +		if (payload & 0x10)
>> +			ret = arm_spe_pkt_snprintf(&err, &buf, &blen, " TLB-ACCESS");
>> +		if (payload & 0x20)
>> +			ret = arm_spe_pkt_snprintf(&err, &buf, &blen, " TLB-REFILL");
>> +		if (payload & 0x40)
>> +			ret = arm_spe_pkt_snprintf(&err, &buf, &blen, " NOT-TAKEN");
>> +		if (payload & 0x80)
>> +			ret = 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)
>> +				ret = arm_spe_pkt_snprintf(&err, &buf, &blen, " LLC-ACCESS");
>> +			if (payload & 0x200)
>> +				ret = arm_spe_pkt_snprintf(&err, &buf, &blen, " LLC-REFILL");
>> +			if (payload & 0x400)
>> +				ret = arm_spe_pkt_snprintf(&err, &buf, &blen, " REMOTE-ACCESS");
>>  		}
>>  		if (ret < 0)
>>  			return ret;
>>  		blen -= ret;
>>  		return 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");
>> +		case 1:
>> +			ret = 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)
>> +					ret = arm_spe_pkt_snprintf(&err, &buf, &blen, " AT");
>> +				if (payload & 0x8)
>> +					ret = arm_spe_pkt_snprintf(&err, &buf, &blen, " EXCL");
>> +				if (payload & 0x10)
>> +					ret = arm_spe_pkt_snprintf(&err, &buf, &blen, " AR");
>>  			} else if (payload & 0x4) {
>> -				ret = snprintf(buf, buf_len, " SIMD-FP");
>> -				buf += ret;
>> -				blen -= ret;
>> +				ret = arm_spe_pkt_snprintf(&err, &buf, &blen, " SIMD-FP");
>>  			}
>> +
>>  			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;
>> -			}
>> +		case 2:
>> +			ret = arm_spe_pkt_snprintf(&err, &buf, &blen, "B");
>> +
>> +			if (payload & 0x1)
>> +				ret = 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;
>> -			}
>> -		default: return 0;
>> +
>> +		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);
>> +		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 3:	ns = !!(packet->payload & NS_FLAG);
>> +		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:
>> +		ret = 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:
>> +			ret = arm_spe_pkt_snprintf(&err, &buf, &blen, "TOT");
>> +			break;
>> +		case 1:
>> +			ret = arm_spe_pkt_snprintf(&err, &buf, &blen, "ISSUE");
>> +			break;
>> +		case 2:
>> +			ret = arm_spe_pkt_snprintf(&err, &buf, &blen, "XLAT");
>> +			break;
>> +		default:
>> +			ret = 0;
>> +			break;
>>  		}
>>  		if (ret < 0)
>>  			return ret;
>>  		blen -= ret;
>>  		return 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);
>>  }
>> -- 
>> 2.17.1
>>
>