Re: [PATCH 16/16] perf probe: Support probing at absolute addresses

[Arnaldo Carvalho de Melo <acme@kernel.org>]

Em Wed, Aug 26, 2015 at 12:00:56AM +0000, 平松雅巳 / HIRAMATU，MASAMI escreveu:
> Arnaldo, I don't think we need "+". 

What would be the problem? When we write


 perf probe /lib/x86_64-linux-gnu/libc-2.19.so +0xeb860

What we're meaning is: Take the address where libc-2.19.so is loaded, in
each process, add (+) to that address the number 0xeb860 (an offset),
and when that probe is enabled, put a breakpoint there.

I saw it that way and thus to me it seemed really natural, thus I
applied.

> So, Nak it.

I don't have strong feelings about that one and I saw that there was a
long discussion, so I'll read it and process the patches, if I don't see
anything questionable.

Next time I'll try not to process perf probe patches so fast :-)

- Arnaldo
 
> > -----Original Message-----
> > From: Arnaldo Carvalho de Melo [mailto:acme@kernel.org]
> > Sent: Wednesday, August 26, 2015 1:15 AM
> > To: Ingo Molnar
> > Cc: linux-kernel@vger.kernel.org; Wang Nan; 平松雅巳 / HIRAMATU，MASAMI; Namhyung Kim; pi3orama@163.com; Arnaldo Carvalho
> > de Melo
> > Subject: [!][PATCH 16/16] perf probe: Support probing at absolute addresses
> > 
> > From: Wang Nan <wangnan0@huawei.com>
> > 
> > It should be useful to allow 'perf probe' probe at absolute offsets of a
> > target.
> > 
> > For example, when (u)probing at a instruction of a shared object in an
> > embedded system where debuginfo is not available 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
> > 
> > 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.
> > 
> > Committer note:
> > 
> > One can as well specify a name, so that the probe doesn't get assigned a
> > generic one starting with abs_, i.e. if we use as described above we
> > get:
> > 
> >   [root@zoo ~]# readelf -sW  /lib64/libc-2.20.so | grep -w malloc
> >     1175: 00000000000830f0   300 FUNC    GLOBAL DEFAULT   12 malloc@@GLIBC_2.2.5
> >      813: 0000000000000000     0 FILE    LOCAL  DEFAULT  ABS malloc.c
> >     5276: 00000000000830f0   300 FUNC    GLOBAL DEFAULT   12 malloc
> >   [root@zoo ~]#
> >   [root@zoo ~]# perf probe /lib64/libc-2.20.so +0x830f0
> >   Added new event:
> >     probe_libc:abs_830f0 (on 0x830f0 in /lib64/libc-2.20.so)
> > 
> >   You can now use it in all perf tools, such as:
> > 
> > 	perf record -e probe_libc:abs_830f0 -aR sleep 1
> > 
> >   [root@zoo ~]#
> >   [root@zoo ~]# perf probe -l
> >     probe_libc:abs_830f0 (on __libc_malloc@glibc-2.20/malloc/malloc.c in /lib64/libc-2.20.so)
> >   [root@zoo ~]#
> > 
> > Whereas if we assign it a name it gets more manageable:
> > 
> >   [root@zoo ~]# perf probe /lib64/libc-2.20.so malloc=+0x830f0
> >   Added new event:
> >     probe_libc:malloc    (on 0x830f0 in /lib64/libc-2.20.so)
> > 
> >   You can now use it in all perf tools, such as:
> > 
> > 	perf record -e probe_libc:malloc -aR sleep 1
> > 
> >   [root@zoo ~]# perf probe -l
> >     probe_libc:malloc    (on __libc_malloc@glibc-2.20/malloc/malloc.c in /lib64/libc-2.20.so)
> >   [root@zoo ~]#
> > 
> > Both, of course, will produce the same results, and we can use a
> > non canonical name, if the need arises:
> > 
> >   [root@zoo ~]# perf probe /lib64/libc-2.20.so memory_allocation=+0x830f0
> >   Added new event:
> >     probe_libc:memory_allocation (on 0x830f0 in /lib64/libc-2.20.so)
> > 
> >   You can now use it in all perf tools, such as:
> > 
> > 	perf record -e probe_libc:memory_allocation -aR sleep 1
> > 
> >   [root@zoo ~]# perf probe -l
> >     probe_libc:memory_allocation (on __libc_malloc@glibc-2.20/malloc/malloc.c in /lib64/libc-2.20.so)
> >   [root@zoo ~]#
> > 
> > Signed-off-by: Wang Nan <wangnan0@huawei.com>
> > Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
> > Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
> > Cc: Namhyung Kim <namhyung@kernel.org>
> > Cc: pi3orama@163.com
> > Link: http://lkml.kernel.org/r/1440509256-193590-2-git-send-email-wangnan0@huawei.com
> > Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
> > ---
> >  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 6c7e538c9b8b..59de69a4e3ac 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 83ee95e9743b..174a3cf6c03d 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 7b80f8cb62b9..29c43c0680a8 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);
> > --
> > 2.1.0
>