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

[Leo Yan <leo.yan@linaro.org>]

On Thu, Oct 08, 2020 at 02:46:06PM +0100, André Przywara wrote:
> 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.

Good point.  '..., "%s", name)' format is more reliable, will change
to use it.

> > +	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!

Exactly, I will update the commit log so can give more explicit info.

Thanks a lot,
Leo

> 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);
> >  }
> > 
>