Messages in this thread Patch in this message | | | Date | Wed, 11 Nov 2020 15:53:20 +0000 | From | Dave Martin <> | Subject | Re: [PATCH v8 06/22] perf arm-spe: Refactor printing string to buffer |
| |
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@arm.com> > Signed-off-by: Leo Yan <leo.yan@linaro.org> > Reviewed-by: Andre Przywara <andre.przywara@arm.com>
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
| |