Re: [PATCH v2 05/14] perf arm-spe: Refactor printing string to buffer

["André Przywara" <andre.przywara@arm.com>]

On 29/09/2020 14:39, Leo Yan wrote:

Hi,

> 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.

Ah, many thanks for tackling this, I wondered about those code
duplications and missing error handling already.

So I tried some sed pattern on the "old" part of the patch, to get to
the new format and spot any differences apart from mechanically changing
"snprintf(buf, buf_len," to "arm_spe_pkt_snprintf(&buf, &blen,".
See below.

> 
> Suggested-by: Dave Martin <Dave.Martin@arm.com>
> Signed-off-by: Leo Yan <leo.yan@linaro.org>

Very nice cleanup! If you can address this one '"%s", name' comment
below, then:

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 4f0aeb62e97b..96b717a19163 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"
>  
> @@ -256,192 +257,214 @@ 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;
> +}
> +
>  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, name);

Isn't it considered safer to use '..., "%s", name)', because that would
handle percent signs in "name" correctly?
Not really an issue in the current code, but good style, I believe.

> +	case ARM_SPE_EVENTS:
> +		ret = arm_spe_pkt_snprintf(&buf, &blen, "EV");
> +		if (ret < 0)
> +			return ret;
> +
>  		if (payload & 0x1) {
> -			ret = snprintf(buf, buf_len, " EXCEPTION-GEN");

So this was actually a bug before, right? Because "buf" does no longer
have buf_len bytes available at this point, it should have been blen
here already. Which gets fixed with all your changes!

Thanks!
Andre

> -			buf += ret;
> -			blen -= ret;
> +			ret = arm_spe_pkt_snprintf(&buf, &blen, " EXCEPTION-GEN");
> +			if (ret < 0)
> +				return ret;
>  		}
>  		if (payload & 0x2) {
> -			ret = snprintf(buf, buf_len, " RETIRED");
> -			buf += ret;
> -			blen -= ret;
> +			ret = arm_spe_pkt_snprintf(&buf, &blen, " RETIRED");
> +			if (ret < 0)
> +				return ret;
>  		}
>  		if (payload & 0x4) {
> -			ret = snprintf(buf, buf_len, " L1D-ACCESS");
> -			buf += ret;
> -			blen -= ret;
> +			ret = arm_spe_pkt_snprintf(&buf, &blen, " L1D-ACCESS");
> +			if (ret < 0)
> +				return ret;
>  		}
>  		if (payload & 0x8) {
> -			ret = snprintf(buf, buf_len, " L1D-REFILL");
> -			buf += ret;
> -			blen -= ret;
> +			ret = arm_spe_pkt_snprintf(&buf, &blen, " L1D-REFILL");
> +			if (ret < 0)
> +				return ret;
>  		}
>  		if (payload & 0x10) {
> -			ret = snprintf(buf, buf_len, " TLB-ACCESS");
> -			buf += ret;
> -			blen -= ret;
> +			ret = arm_spe_pkt_snprintf(&buf, &blen, " TLB-ACCESS");
> +			if (ret < 0)
> +				return ret;
>  		}
>  		if (payload & 0x20) {
> -			ret = snprintf(buf, buf_len, " TLB-REFILL");
> -			buf += ret;
> -			blen -= ret;
> +			ret = arm_spe_pkt_snprintf(&buf, &blen, " TLB-REFILL");
> +			if (ret < 0)
> +				return ret;
>  		}
>  		if (payload & 0x40) {
> -			ret = snprintf(buf, buf_len, " NOT-TAKEN");
> -			buf += ret;
> -			blen -= ret;
> +			ret = arm_spe_pkt_snprintf(&buf, &blen, " NOT-TAKEN");
> +			if (ret < 0)
> +				return ret;
>  		}
>  		if (payload & 0x80) {
> -			ret = snprintf(buf, buf_len, " MISPRED");
> -			buf += ret;
> -			blen -= ret;
> +			ret = arm_spe_pkt_snprintf(&buf, &blen, " MISPRED");
> +			if (ret < 0)
> +				return ret;
>  		}
>  		if (idx > 1) {
>  			if (payload & 0x100) {
> -				ret = snprintf(buf, buf_len, " LLC-ACCESS");
> -				buf += ret;
> -				blen -= ret;
> +				ret = arm_spe_pkt_snprintf(&buf, &blen, " LLC-ACCESS");
> +				if (ret < 0)
> +					return ret;
>  			}
>  			if (payload & 0x200) {
> -				ret = snprintf(buf, buf_len, " LLC-REFILL");
> -				buf += ret;
> -				blen -= ret;
> +				ret = arm_spe_pkt_snprintf(&buf, &blen, " LLC-REFILL");
> +				if (ret < 0)
> +					return ret;
>  			}
>  			if (payload & 0x400) {
> -				ret = snprintf(buf, buf_len, " REMOTE-ACCESS");
> -				buf += ret;
> -				blen -= ret;
> +				ret = arm_spe_pkt_snprintf(&buf, &blen, " REMOTE-ACCESS");
> +				if (ret < 0)
> +					return ret;
>  			}
>  		}
> -		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;
> -
> -			if (payload & 0x1)
> -				ret = snprintf(buf, buf_len, "ST");
> -			else
> -				ret = snprintf(buf, buf_len, "LD");
> -			buf += ret;
> -			blen -= ret;
> +		case 0:
> +			return arm_spe_pkt_snprintf(&buf, &blen,
> +					payload & 0x1 ? "COND-SELECT" : "INSN-OTHER");
> +		case 1:
> +			ret = arm_spe_pkt_snprintf(&buf, &blen,
> +						   payload & 0x1 ? "ST" : "LD");
> +			if (ret < 0)
> +				return ret;
> +
>  			if (payload & 0x2) {
>  				if (payload & 0x4) {
> -					ret = snprintf(buf, buf_len, " AT");
> -					buf += ret;
> -					blen -= ret;
> +					ret = arm_spe_pkt_snprintf(&buf, &blen, " AT");
> +					if (ret < 0)
> +						return ret;
>  				}
>  				if (payload & 0x8) {
> -					ret = snprintf(buf, buf_len, " EXCL");
> -					buf += ret;
> -					blen -= ret;
> +					ret = arm_spe_pkt_snprintf(&buf, &blen, " EXCL");
> +					if (ret < 0)
> +						return ret;
>  				}
>  				if (payload & 0x10) {
> -					ret = snprintf(buf, buf_len, " AR");
> -					buf += ret;
> -					blen -= ret;
> +					ret = arm_spe_pkt_snprintf(&buf, &blen, " AR");
> +					if (ret < 0)
> +						return ret;
>  				}
>  			} else if (payload & 0x4) {
> -				ret = snprintf(buf, buf_len, " SIMD-FP");
> -				buf += ret;
> -				blen -= ret;
> +				ret = arm_spe_pkt_snprintf(&buf, &blen, " SIMD-FP");
> +				if (ret < 0)
> +					return ret;
>  			}
> +
> +			return buf_len - blen;
> +
> +		case 2:
> +			ret = arm_spe_pkt_snprintf(&buf, &blen, "B");
>  			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;
> +				ret = arm_spe_pkt_snprintf(&buf, &blen, " COND");
> +				if (ret < 0)
> +					return ret;
>  			}
>  			if (payload & 0x2) {
> -				ret = snprintf(buf, buf_len, " IND");
> -				buf += ret;
> -				blen -= ret;
> +				ret = arm_spe_pkt_snprintf(&buf, &blen, " IND");
> +				if (ret < 0)
> +					return ret;
>  			}
> -			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(&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(&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(&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(&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;
> -		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;
> -		}
> +		return arm_spe_pkt_snprintf(&buf, &blen, "%s 0x%lx el%d",
> +					    name, (unsigned long)payload, idx + 1);
> +	case ARM_SPE_COUNTER:
> +		ret = arm_spe_pkt_snprintf(&buf, &blen, "%s %d ", name,
> +					   (unsigned short)payload);
>  		if (ret < 0)
>  			return ret;
> -		blen -= ret;
> +
> +		switch (idx) {
> +		case 0:
> +			ret = arm_spe_pkt_snprintf(&buf, &blen, "TOT");
> +			if (ret < 0)
> +				return ret;
> +			break;
> +		case 1:
> +			ret = arm_spe_pkt_snprintf(&buf, &blen, "ISSUE");
> +			if (ret < 0)
> +				return ret;
> +			break;
> +		case 2:
> +			ret = arm_spe_pkt_snprintf(&buf, &blen, "XLAT");
> +			if (ret < 0)
> +				return ret;
> +			break;
> +		default:
> +			break;
> +		}
> +
>  		return buf_len - blen;
> -	}
> +
>  	default:
>  		break;
>  	}
>  
> -	return snprintf(buf, buf_len, "%s 0x%llx (%d)",
> -			name, payload, packet->index);
> +	return arm_spe_pkt_snprintf(&buf, &blen, "%s 0x%llx (%d)",
> +				    name, payload, packet->index);
>  }
>