Re: [PATCH v8 06/22] perf arm-spe: Refactor printing string to buffer
From: Dave Martin
Date: Wed Nov 11 2020 - 10:53:29 EST
On Wed, Nov 11, 2020 at 07:11:33AM +0000, 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().
>
> 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>
> Reviewed-by: Andre Przywara <andre.przywara@xxxxxxx>
Mostly looks fine to me now, thought there are a few potentionalu
issues -- comments below.
Cheers
---Dave
> ---
> .../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.
> + */
(*blen - 1) chars, + 1 for '\0', is exactly *blen bytes. So ret ==
*blen - 1 is not an error.
> + } else if (ret >= ((int)*blen - 1)) {
So I suggest
if (ret >= *blen)
here.
Nit: If gcc moans about signedness in the comparison, I think it's
preferable to say
if ((size_t)ret >= *blen)
rather than casting *blen to an int. We already know that ret >= 0, and
UINT_MAX always fits in a size_t. On this code path it probably doesn't
matter in practice through, since *blen will be much less than INT_MAX.
vsnprintf() probably doesn't cope gracefully with super-large buffers
anyway, and the ISO C standards don't describe this situation
adequately.
If gcc doesn't warn, just drop the cast.
> + (*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");
> + 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;
I thought that arm_spe_pkt_snprintf() already did this subtraction?
Also, arm_spe_pkt_snprintf() can return a value >= blen if it overflows
the buffer, so I think this subtraction can underflow away.
If you always do the subtraction at the and of arm_spe_pkt_snprintf()
rather than outside, and if arm_spe_pkt_snprintf() subtracts no more
than blen - 1, then I think this all just works.
> 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;
Same here.
> 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;
Is it my imagination, or does every case that doesn't end in a break
have the same sequence here?
Can we just break and put
if (err)
return err;
at the end of the big switch?
I'm assuming that the caller treats any nonzero value as an error -- I
seem to remeber you mentioning this previously?
[...]
Cheers
---Dave