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perf probe: Add --range option to show a variable's location range

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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: He Kuang <hekuang@huawei.com>
Acked-by: Masami 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: Arnaldo Carvalho de Melo <acme@redhat.com>
This commit is contained in:
He Kuang 2015-05-11 09:25:03 +00:00 committed by Arnaldo Carvalho de Melo
parent fb9596d173
commit 349e8d2611
5 changed files with 170 additions and 13 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
tools/perf/builtin-probe.c
View File

@ -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,

121
tools/perf/util/dwarf-aux.c
View File

@ -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;
}

2
tools/perf/util/dwarf-aux.h
View File

@ -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

1
tools/perf/util/probe-event.h
View File

@ -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;

57
tools/perf/util/probe-finder.c
View File

@ -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 @@ found:
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_var:
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_var:
}
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_var:
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));
}