RE: [PATCH 2/2] perf probe: Support probing at absolute address

[åæéå / HIRAMATUïMASAMI]

> From: Wangnan (F) [mailto:wangnan0@xxxxxxxxxx] 
> 
> On 2015/8/26 8:02, åæéå / HIRAMATUïMASAMI wrote:
> >> From: Wang Nan [mailto:wangnan0@xxxxxxxxxx]
> >>
> >> It should be useful to allow 'perf probe' probe at absolute offset of
> >> a target. For example, when (u)probing at a instruction of a shared
> >> object in a embedded system where debuginfo is not avaliable but we
> >> know the offset of that instruction by manually digging.
> >>
> >> This patch enables following perf probe command syntax:
> >>
> >>   # perf probe +0xffffffff811e6615
> >>
> >> And
> >>
> >>   # perf probe /lib/x86_64-linux-gnu/libc-2.19.so +0xeb860
> > Why do we need "+" for the absolute address?
> > It seems that we can do it if we find that the given probe point
> > starts with "0x".
> >
> > Thanks,
> 
> I will change 2/2 as you suggection.
> 
> However, we can only ensure that in kernel side symbol never leading
> with '0x'. Although I don't think symbol leading with 0x is useful,
> it is still possible for a userspace program compiled and linked by
> a language other than C produces such symbol. '+' helps us separate
> address and function name semantically, make us don't rely on assumption
> on function names. If in future we do meet '0x' symbols, I think we still
> need the '+' syntax back. But we can do it at that time.

Agreed, if we really find the case, we can add '+' prefix support
just for an optional expression :)

Thank you!

> 
> Thank you.
> 
> 
> >> In the above example, we don't need a anchor symbol, so it is possible
> >> to compute absolute addresses using other methods and then use
> >> 'perf probe' to create the probing points.
> >>
> >> Signed-off-by: Wang Nan <wangnan0@xxxxxxxxxx>
> >> Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
> >> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> >> Cc: Masami Hiramatsu <masami.hiramatsu.pt@xxxxxxxxxxx>
> >> Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
> >> ---
> >>   tools/perf/util/probe-event.c  | 144 +++++++++++++++++++++++++++++++++++++----
> >>   tools/perf/util/probe-event.h  |   3 +
> >>   tools/perf/util/probe-finder.c |  21 +-----
> >>   3 files changed, 138 insertions(+), 30 deletions(-)
> >>
> >> diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
> >> index 6c7e538..59de69a4 100644
> >> --- a/tools/perf/util/probe-event.c
> >> +++ b/tools/perf/util/probe-event.c
> >> @@ -1194,9 +1194,13 @@ static int parse_perf_probe_point(char *arg, struct perf_probe_event *pev)
> >>   		*ptr++ = '\0';
> >>   	}
> >>
> >> -	tmp = strdup(arg);
> >> -	if (tmp == NULL)
> >> -		return -ENOMEM;
> >> +	if (arg[0] == '\0')
> >> +		tmp = NULL;
> >> +	else {
> >> +		tmp = strdup(arg);
> >> +		if (tmp == NULL)
> >> +			return -ENOMEM;
> >> +	}
> >>
> >>   	if (file_spec)
> >>   		pp->file = tmp;
> >> @@ -1283,11 +1287,6 @@ static int parse_perf_probe_point(char *arg, struct perf_probe_event *pev)
> >>   		return -EINVAL;
> >>   	}
> >>
> >> -	if (pp->offset && !pp->function) {
> >> -		semantic_error("Offset requires an entry function.\n");
> >> -		return -EINVAL;
> >> -	}
> >> -
> >>   	if (pp->retprobe && !pp->function) {
> >>   		semantic_error("Return probe requires an entry function.\n");
> >>   		return -EINVAL;
> >> @@ -1299,6 +1298,11 @@ static int parse_perf_probe_point(char *arg, struct perf_probe_event *pev)
> >>   		return -EINVAL;
> >>   	}
> >>
> >> +	if (!pp->function && !pp->offset && !pp->file) {
> >> +		semantic_error("Absolute address should not be zero.\n");
> >> +		return -EINVAL;
> >> +	}
> >> +
> >>   	pr_debug("symbol:%s file:%s line:%d offset:%lu return:%d lazy:%s\n",
> >>   		 pp->function, pp->file, pp->line, pp->offset, pp->retprobe,
> >>   		 pp->lazy_line);
> >> @@ -1609,7 +1613,7 @@ error:
> >>   static char *synthesize_perf_probe_point(struct perf_probe_point *pp)
> >>   {
> >>   	char *buf, *tmp;
> >> -	char offs[32] = "", line[32] = "", file[32] = "";
> >> +	char offs[32] = "", line[32] = "", file[32] = "", addr[32] = "";
> >>   	int ret, len;
> >>
> >>   	buf = zalloc(MAX_CMDLEN);
> >> @@ -1622,6 +1626,11 @@ static char *synthesize_perf_probe_point(struct perf_probe_point *pp)
> >>   		if (ret <= 0)
> >>   			goto error;
> >>   	}
> >> +	if (!pp->function) {
> >> +		ret = e_snprintf(addr, 32, "0x%lx", pp->offset);
> >> +		if (ret <= 0)
> >> +			goto error;
> >> +	}
> >>   	if (pp->line) {
> >>   		ret = e_snprintf(line, 32, ":%d", pp->line);
> >>   		if (ret <= 0)
> >> @@ -1639,9 +1648,11 @@ static char *synthesize_perf_probe_point(struct perf_probe_point *pp)
> >>   			goto error;
> >>   	}
> >>
> >> -	if (pp->function)
> >> -		ret = e_snprintf(buf, MAX_CMDLEN, "%s%s%s%s%s", pp->function,
> >> -				 offs, pp->retprobe ? "%return" : "", line,
> >> +	if (pp->function || pp->offset)
> >> +		ret = e_snprintf(buf, MAX_CMDLEN, "%s%s%s%s%s",
> >> +				 pp->function ? : addr,
> >> +				 pp->function ? offs : "",
> >> +				 pp->retprobe ? "%return" : "", line,
> >>   				 file);
> >>   	else
> >>   		ret = e_snprintf(buf, MAX_CMDLEN, "%s%s", file, line);
> >> @@ -1786,6 +1797,11 @@ char *synthesize_probe_trace_command(struct probe_trace_event *tev)
> >>   	if (tev->uprobes)
> >>   		ret = e_snprintf(buf + len, MAX_CMDLEN - len, "%s:0x%lx",
> >>   				 tp->module, tp->address);
> >> +	else if (tp->symbol[0] == '0' && tp->symbol[1] == 'x')
> >> +		/* Absolute address. See try_to_find_absolute_address() */
> >> +		ret = e_snprintf(buf + len, MAX_CMDLEN - len, "%s%s0x%lx",
> >> +				 tp->module ?: "", tp->module ? ":" : "",
> >> +				 tp->address);
> >>   	else
> >>   		ret = e_snprintf(buf + len, MAX_CMDLEN - len, "%s%s%s+%lu",
> >>   				 tp->module ?: "", tp->module ? ":" : "",
> >> @@ -2572,6 +2588,87 @@ err_out:
> >>   	goto out;
> >>   }
> >>
> >> +static int try_to_find_absolute_address(struct perf_probe_event *pev,
> >> +					struct probe_trace_event **tevs)
> >> +{
> >> +	struct perf_probe_point *pp = &pev->point;
> >> +	struct probe_trace_event *tev;
> >> +	struct probe_trace_point *tp;
> >> +	int i, err;
> >> +
> >> +	if (perf_probe_event_need_dwarf(pev) || pev->point.function)
> >> +		return -EINVAL;
> >> +
> >> +	/*
> >> +	 * This is 'perf probe /lib/libc.so +0xabcd'. Try to probe at
> >> +	 * absolute address.
> >> +	 *
> >> +	 * Only one tev can be generated by this.
> >> +	 */
> >> +	*tevs = zalloc(sizeof(*tev));
> >> +	if (!*tevs)
> >> +		return -ENOMEM;
> >> +
> >> +	tev = *tevs;
> >> +	tp = &tev->point;
> >> +
> >> +	/*
> >> +	 * Don't use tp->offset, use address directly, because
> >> +	 * in synthesize_probe_trace_command() address cannot be
> >> +	 * zero.
> >> +	 */
> >> +	tp->address = pev->point.offset;
> >> +	tp->retprobe = pp->retprobe;
> >> +	tev->uprobes = pev->uprobes;
> >> +
> >> +	err = -ENOMEM;
> >> +	/* Give it a '0x' leading symbol name */
> >> +	if (asprintf(&tp->symbol, "0x%lx", tp->address) < 0)
> >> +		goto errout;
> >> +
> >> +	/* For kprobe, check range */
> >> +	if ((!tev->uprobes) &&
> >> +	    (kprobe_warn_out_range(tev->point.symbol,
> >> +				   tev->point.address))) {
> >> +		err = -EACCES;
> >> +		goto errout;
> >> +	}
> >> +
> >> +	if (asprintf(&tp->realname, "abs_%lx", tp->address) < 0)
> >> +		goto errout;
> >> +
> >> +	if (pev->target) {
> >> +		tp->module = strdup(pev->target);
> >> +		if (!tp->module)
> >> +			goto errout;
> >> +	}
> >> +
> >> +	if (tev->group) {
> >> +		tev->group = strdup(pev->group);
> >> +		if (!tev->group)
> >> +			goto errout;
> >> +	}
> >> +
> >> +	if (pev->event) {
> >> +		tev->event = strdup(pev->event);
> >> +		if (!tev->event)
> >> +			goto errout;
> >> +	}
> >> +
> >> +	tev->nargs = pev->nargs;
> >> +	for (i = 0; i < tev->nargs; i++)
> >> +		copy_to_probe_trace_arg(&tev->args[i], &pev->args[i]);
> >> +
> >> +	return 1;
> >> +
> >> +errout:
> >> +	if (*tevs) {
> >> +		clear_probe_trace_events(*tevs, 1);
> >> +		*tevs = NULL;
> >> +	}
> >> +	return err;
> >> +}
> >> +
> >>   bool __weak arch__prefers_symtab(void) { return false; }
> >>
> >>   static int convert_to_probe_trace_events(struct perf_probe_event *pev,
> >> @@ -2588,6 +2685,10 @@ static int convert_to_probe_trace_events(struct perf_probe_event *pev,
> >>   		}
> >>   	}
> >>
> >> +	ret = try_to_find_absolute_address(pev, tevs);
> >> +	if (ret > 0)
> >> +		return ret;
> >> +
> >>   	if (arch__prefers_symtab() && !perf_probe_event_need_dwarf(pev)) {
> >>   		ret = find_probe_trace_events_from_map(pev, tevs);
> >>   		if (ret > 0)
> >> @@ -2758,3 +2859,22 @@ end:
> >>   	return ret;
> >>   }
> >>
> >> +int copy_to_probe_trace_arg(struct probe_trace_arg *tvar,
> >> +			    struct perf_probe_arg *pvar)
> >> +{
> >> +	tvar->value = strdup(pvar->var);
> >> +	if (tvar->value == NULL)
> >> +		return -ENOMEM;
> >> +	if (pvar->type) {
> >> +		tvar->type = strdup(pvar->type);
> >> +		if (tvar->type == NULL)
> >> +			return -ENOMEM;
> >> +	}
> >> +	if (pvar->name) {
> >> +		tvar->name = strdup(pvar->name);
> >> +		if (tvar->name == NULL)
> >> +			return -ENOMEM;
> >> +	} else
> >> +		tvar->name = NULL;
> >> +	return 0;
> >> +}
> >> diff --git a/tools/perf/util/probe-event.h b/tools/perf/util/probe-event.h
> >> index 83ee95e..174a3cf 100644
> >> --- a/tools/perf/util/probe-event.h
> >> +++ b/tools/perf/util/probe-event.h
> >> @@ -156,4 +156,7 @@ int e_snprintf(char *str, size_t size, const char *format, ...)
> >>   /* Maximum index number of event-name postfix */
> >>   #define MAX_EVENT_INDEX	1024
> >>
> >> +int copy_to_probe_trace_arg(struct probe_trace_arg *tvar,
> >> +			    struct perf_probe_arg *pvar);
> >> +
> >>   #endif /*_PROBE_EVENT_H */
> >> diff --git a/tools/perf/util/probe-finder.c b/tools/perf/util/probe-finder.c
> >> index 7b80f8c..29c43c068 100644
> >> --- a/tools/perf/util/probe-finder.c
> >> +++ b/tools/perf/util/probe-finder.c
> >> @@ -553,24 +553,9 @@ static int find_variable(Dwarf_Die *sc_die, struct probe_finder *pf)
> >>   	char buf[32], *ptr;
> >>   	int ret = 0;
> >>
> >> -	if (!is_c_varname(pf->pvar->var)) {
> >> -		/* Copy raw parameters */
> >> -		pf->tvar->value = strdup(pf->pvar->var);
> >> -		if (pf->tvar->value == NULL)
> >> -			return -ENOMEM;
> >> -		if (pf->pvar->type) {
> >> -			pf->tvar->type = strdup(pf->pvar->type);
> >> -			if (pf->tvar->type == NULL)
> >> -				return -ENOMEM;
> >> -		}
> >> -		if (pf->pvar->name) {
> >> -			pf->tvar->name = strdup(pf->pvar->name);
> >> -			if (pf->tvar->name == NULL)
> >> -				return -ENOMEM;
> >> -		} else
> >> -			pf->tvar->name = NULL;
> >> -		return 0;
> >> -	}
> >> +	/* Copy raw parameters */
> >> +	if (!is_c_varname(pf->pvar->var))
> >> +		return copy_to_probe_trace_arg(pf->tvar, pf->pvar);
> >>
> >>   	if (pf->pvar->name)
> >>   		pf->tvar->name = strdup(pf->pvar->name);
> >> --
> >> 1.8.3.4
> 

N‹§²æ¸›yú²X¬¶ÇvØ–)Þ{.nlj·¥Š{±‘êX§¶›¡Ü}©ž²ÆzÚj:+v‰¨¾«‘êZ+€Êzf£¢·hšˆ§~†­†Ûÿû®w¥¢¸?™¨è&¢)ßf”ùy§m…á«a¶Úÿ0¶ìå