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Subject[tip:perf/core] perf probe: Add --range option to show a variable 's location range
Commit-ID:  349e8d2611316cce11c0b9d0830ebb585c9b82b8
Gitweb: http://git.kernel.org/tip/349e8d2611316cce11c0b9d0830ebb585c9b82b8
Author: He Kuang <hekuang@huawei.com>
AuthorDate: Mon, 11 May 2015 09:25:03 +0000
Committer: Arnaldo Carvalho de Melo <acme@redhat.com>
CommitDate: Tue, 12 May 2015 09:59:50 -0300

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: 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>
---
tools/perf/builtin-probe.c | 2 +
tools/perf/util/dwarf-aux.c | 121 +++++++++++++++++++++++++++++++++++++++++
tools/perf/util/dwarf-aux.h | 2 +
tools/perf/util/probe-event.h | 1 +
tools/perf/util/probe-finder.c | 57 ++++++++++++++-----
5 files changed, 170 insertions(+), 13 deletions(-)

diff --git a/tools/perf/builtin-probe.c b/tools/perf/builtin-probe.c
index 7fa2c7a..1272559 100644
--- a/tools/perf/builtin-probe.c
+++ b/tools/perf/builtin-probe.c
@@ -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,
diff --git a/tools/perf/util/dwarf-aux.c b/tools/perf/util/dwarf-aux.c
index 737c9db..afa0971 100644
--- a/tools/perf/util/dwarf-aux.c
+++ b/tools/perf/util/dwarf-aux.c
@@ -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;
+}
diff --git a/tools/perf/util/dwarf-aux.h b/tools/perf/util/dwarf-aux.h
index 60676fd..c154c0b8 100644
--- a/tools/perf/util/dwarf-aux.h
+++ b/tools/perf/util/dwarf-aux.h
@@ -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
diff --git a/tools/perf/util/probe-event.h b/tools/perf/util/probe-event.h
index 1e2faa3..537eb32 100644
--- a/tools/perf/util/probe-event.h
+++ b/tools/perf/util/probe-event.h
@@ -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;
diff --git a/tools/perf/util/probe-finder.c b/tools/perf/util/probe-finder.c
index d7c2e90..5804086 100644
--- a/tools/perf/util/probe-finder.c
+++ b/tools/perf/util/probe-finder.c
@@ -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));
}

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