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Commit 349e8d26 authored by He Kuang's avatar He Kuang Committed by Arnaldo Carvalho de Melo
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perf probe: Add --range option to show a variable's location range 



It is not easy for users to get the accurate byte offset or the line
number where a local variable can be probed.

With '--range' option, local variables in the scope of the probe point
are showed with a byte offset range, and can be added according to this
range information.

For example, there are some variables in the function
generic_perform_write():

  <generic_perform_write@mm/filemap.c:0>
  0  ssize_t generic_perform_write(struct file *file,
  1                                 struct iov_iter *i, loff_t pos)
  2  {
  3          struct address_space *mapping = file->f_mapping;
  4          const struct address_space_operations *a_ops = mapping->a_ops;
  ...
  42                 status = a_ops->write_begin(file, mapping, pos, bytes, flags,
                                               &page, &fsdata);
  44                 if (unlikely(status < 0))

But we fail when we try to probe the variable 'a_ops' at line 42 or 44.

  $ perf probe --add 'generic_perform_write:42 a_ops'
  Failed to find the location of a_ops at this address.
    Perhaps, it has been optimized out.

This is because the source code do not match the assembly, so a variable
may not be available in the source code line where it appears.

After this patch, we can lookup the accurate byte offset range of a
variable, 'INV' indicates that this variable is not valid at the given
point, but available in the scope:

  $ perf probe --vars 'generic_perform_write:42' --range
  Available variables at generic_perform_write:42
    @<generic_perform_write+141>
       [INV] ssize_t written @<generic_perform_write+[324-331]>
       [INV] struct address_space_operations*        a_ops   @<generic_perform_write+[55-61,170-176,223-246]>
       [VAL] (unknown_type)  fsdata  @<generic_perform_write+[70-307,346-411]>
       [VAL] loff_t  pos     @<generic_perform_write+[0-286,286-336,346-411]>
       [VAL] long int        status  @<generic_perform_write+[83-342,346-411]>
       [VAL] long unsigned int       bytes   @<generic_perform_write+[122-311,320-338,346-403,403-411]>
       [VAL] struct address_space*   mapping @<generic_perform_write+[35-344,346-411]>
       [VAL] struct iov_iter*        i       @<generic_perform_write+[0-340,346-411]>
       [VAL] struct page*    page    @<generic_perform_write+[70-307,346-411]>

Then it is more clear for us to add a probe with this variable:

  $ perf probe --add 'generic_perform_write+170 a_ops'
  Added new event:
    probe:generic_perform_write (on generic_perform_write+170 with a_ops)

Signed-off-by: default avatarHe Kuang <hekuang@huawei.com>
Acked-by: default avatarMasami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/r/1431336304-16863-2-git-send-email-hekuang@huawei.com


Signed-off-by: default avatarArnaldo Carvalho de Melo <acme@redhat.com>
parent fb9596d1

tools/perf/builtin-probe.c

+2 −0
Original line number Diff line number Diff line
@@ -372,6 +372,8 @@ __cmd_probe(int argc, const char **argv, const char *prefix __maybe_unused) 
		     "Show accessible variables on PROBEDEF", opt_show_vars),

	OPT_BOOLEAN('\0', "externs", &probe_conf.show_ext_vars,

		    "Show external variables too (with --vars only)"),

	OPT_BOOLEAN('\0', "range", &probe_conf.show_location_range,

		"Show variables location range in scope (with --vars only)"),

	OPT_STRING('k', "vmlinux", &symbol_conf.vmlinux_name,

		   "file", "vmlinux pathname"),

	OPT_STRING('s', "source", &symbol_conf.source_prefix,

tools/perf/util/dwarf-aux.c

+121 −0
Original line number Diff line number Diff line
@@ -913,3 +913,124 @@ int die_get_varname(Dwarf_Die *vr_die, struct strbuf *buf) 
	return 0;

}



/**

 * die_get_var_innermost_scope - Get innermost scope range of given variable DIE

 * @sp_die: a subprogram DIE

 * @vr_die: a variable DIE

 * @buf: a strbuf for variable byte offset range

 *

 * Get the innermost scope range of @vr_die and stores it in @buf as

 * "@<function_name+[NN-NN,NN-NN]>".

 */

static int die_get_var_innermost_scope(Dwarf_Die *sp_die, Dwarf_Die *vr_die,

				struct strbuf *buf)

{

	Dwarf_Die *scopes;

	int count;

	size_t offset = 0;

	Dwarf_Addr base;

	Dwarf_Addr start, end;

	Dwarf_Addr entry;

	int ret;

	bool first = true;

	const char *name;



	ret = dwarf_entrypc(sp_die, &entry);

	if (ret)

		return ret;



	name = dwarf_diename(sp_die);

	if (!name)

		return -ENOENT;



	count = dwarf_getscopes_die(vr_die, &scopes);



	/* (*SCOPES)[1] is the DIE for the scope containing that scope */

	if (count <= 1) {

		ret = -EINVAL;

		goto out;

	}



	while ((offset = dwarf_ranges(&scopes[1], offset, &base,

				&start, &end)) > 0) {

		start -= entry;

		end -= entry;



		if (first) {

			strbuf_addf(buf, "@<%s+[%lu-%lu",

				name, start, end);

			first = false;

		} else {

			strbuf_addf(buf, ",%lu-%lu",

				start, end);

		}

	}



	if (!first)

		strbuf_addf(buf, "]>");



out:

	free(scopes);

	return ret;

}



/**

 * die_get_var_range - Get byte offset range of given variable DIE

 * @sp_die: a subprogram DIE

 * @vr_die: a variable DIE

 * @buf: a strbuf for type and variable name and byte offset range

 *

 * Get the byte offset range of @vr_die and stores it in @buf as

 * "@<function_name+[NN-NN,NN-NN]>".

 */

int die_get_var_range(Dwarf_Die *sp_die, Dwarf_Die *vr_die, struct strbuf *buf)

{

	int ret = 0;

	Dwarf_Addr base;

	Dwarf_Addr start, end;

	Dwarf_Addr entry;

	Dwarf_Op *op;

	size_t nops;

	size_t offset = 0;

	Dwarf_Attribute attr;

	bool first = true;

	const char *name;



	ret = dwarf_entrypc(sp_die, &entry);

	if (ret)

		return ret;



	name = dwarf_diename(sp_die);

	if (!name)

		return -ENOENT;



	if (dwarf_attr(vr_die, DW_AT_location, &attr) == NULL)

		return -EINVAL;



	while ((offset = dwarf_getlocations(

				&attr, offset, &base,

				&start, &end, &op, &nops)) > 0) {

		if (start == 0) {

			/* Single Location Descriptions */

			ret = die_get_var_innermost_scope(sp_die, vr_die, buf);

			return ret;

		}



		/* Location Lists */

		start -= entry;

		end -= entry;

		if (first) {

			strbuf_addf(buf, "@<%s+[%lu-%lu",

				name, start, end);

			first = false;

		} else {

			strbuf_addf(buf, ",%lu-%lu",

				start, end);

		}

	}



	if (!first)

		strbuf_addf(buf, "]>");



	return ret;

}

tools/perf/util/dwarf-aux.h

+2 −0
Original line number Diff line number Diff line
@@ -121,4 +121,6 @@ extern int die_get_typename(Dwarf_Die *vr_die, struct strbuf *buf); 


/* Get the name and type of given variable DIE, stored as "type\tname" */

extern int die_get_varname(Dwarf_Die *vr_die, struct strbuf *buf);

extern int die_get_var_range(Dwarf_Die *sp_die, Dwarf_Die *vr_die,

			struct strbuf *buf);

#endif

tools/perf/util/probe-event.h

+1 −0
Original line number Diff line number Diff line
@@ -9,6 +9,7 @@ 
/* Probe related configurations */

struct probe_conf {

	bool	show_ext_vars;

	bool	show_location_range;

	bool	force_add;

	bool	no_inlines;

	int	max_probes;

tools/perf/util/probe-finder.c

+44 −13
Original line number Diff line number Diff line
@@ -177,7 +177,7 @@ static int convert_variable_location(Dwarf_Die *vr_die, Dwarf_Addr addr, 
	Dwarf_Word offs = 0;

	bool ref = false;

	const char *regs;

	int ret;

	int ret, ret2 = 0;



	if (dwarf_attr(vr_die, DW_AT_external, &attr) != NULL)

		goto static_var;
@@ -187,9 +187,19 @@ static int convert_variable_location(Dwarf_Die *vr_die, Dwarf_Addr addr, 
		return -EINVAL;	/* Broken DIE ? */

	if (dwarf_getlocation_addr(&attr, addr, &op, &nops, 1) <= 0) {

		ret = dwarf_entrypc(sp_die, &tmp);

		if (ret || addr != tmp ||

		    dwarf_tag(vr_die) != DW_TAG_formal_parameter ||

		    dwarf_highpc(sp_die, &tmp))

		if (ret)

			return -ENOENT;



		if (probe_conf.show_location_range &&

			(dwarf_tag(vr_die) == DW_TAG_variable)) {

			ret2 = -ERANGE;

		} else if (addr != tmp ||

			dwarf_tag(vr_die) != DW_TAG_formal_parameter) {

			return -ENOENT;

		}



		ret = dwarf_highpc(sp_die, &tmp);

		if (ret)

			return -ENOENT;

		/*

		 * This is fuzzed by fentry mcount. We try to find the
@@ -210,7 +220,7 @@ static int convert_variable_location(Dwarf_Die *vr_die, Dwarf_Addr addr, 
	if (op->atom == DW_OP_addr) {

static_var:

		if (!tvar)

			return 0;

			return ret2;

		/* Static variables on memory (not stack), make @varname */

		ret = strlen(dwarf_diename(vr_die));

		tvar->value = zalloc(ret + 2);
@@ -220,7 +230,7 @@ static int convert_variable_location(Dwarf_Die *vr_die, Dwarf_Addr addr, 
		tvar->ref = alloc_trace_arg_ref((long)offs);

		if (tvar->ref == NULL)

			return -ENOMEM;

		return 0;

		return ret2;

	}



	/* If this is based on frame buffer, set the offset */
@@ -250,14 +260,14 @@ static int convert_variable_location(Dwarf_Die *vr_die, Dwarf_Addr addr, 
	}



	if (!tvar)

		return 0;

		return ret2;



	regs = get_arch_regstr(regn);

	if (!regs) {

		/* This should be a bug in DWARF or this tool */

		pr_warning("Mapping for the register number %u "

			   "missing on this architecture.\n", regn);

		return -ERANGE;

		return -ENOTSUP;

	}



	tvar->value = strdup(regs);
@@ -269,7 +279,7 @@ static int convert_variable_location(Dwarf_Die *vr_die, Dwarf_Addr addr, 
		if (tvar->ref == NULL)

			return -ENOMEM;

	}

	return 0;

	return ret2;

}



#define BYTES_TO_BITS(nb)	((nb) * BITS_PER_LONG / sizeof(long))
@@ -1270,13 +1280,34 @@ static int collect_variables_cb(Dwarf_Die *die_mem, void *data) 
		ret = convert_variable_location(die_mem, af->pf.addr,

						af->pf.fb_ops, &af->pf.sp_die,

						NULL);

		if (ret == 0) {

		if (ret == 0 || ret == -ERANGE) {

			int ret2;

			bool externs = !af->child;

			struct strbuf buf;



			strbuf_init(&buf, 64);

			ret = die_get_varname(die_mem, &buf);

			pr_debug2("Add new var: %s\n", buf.buf);

			if (ret == 0) {



			if (probe_conf.show_location_range) {

				if (!externs) {

					if (ret)

						strbuf_addf(&buf, "[INV]\t");

					else

						strbuf_addf(&buf, "[VAL]\t");

				} else

					strbuf_addf(&buf, "[EXT]\t");

			}



			ret2 = die_get_varname(die_mem, &buf);



			if (!ret2 && probe_conf.show_location_range &&

				!externs) {

				strbuf_addf(&buf, "\t");

				ret2 = die_get_var_range(&af->pf.sp_die,

							die_mem, &buf);

			}



			pr_debug("Add new var: %s\n", buf.buf);

			if (ret2 == 0) {

				strlist__add(vl->vars,

					strbuf_detach(&buf, NULL));

			}