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authorHe Kuang <hekuang@huawei.com>2015-05-11 09:25:03 +0000
committerArnaldo Carvalho de Melo <acme@redhat.com>2015-05-12 09:59:50 -0300
commit349e8d2611316cce11c0b9d0830ebb585c9b82b8 (patch)
treeb985e93cd47f709e010eac3290bee3dbc3dba9d2 /tools/perf/util/dwarf-aux.c
parentfb9596d1731cc37da6489de439f8b876f3a12db2 (diff)
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>
Diffstat (limited to 'tools/perf/util/dwarf-aux.c')
-rw-r--r--tools/perf/util/dwarf-aux.c121
1 files changed, 121 insertions, 0 deletions
diff --git a/tools/perf/util/dwarf-aux.c b/tools/perf/util/dwarf-aux.c
index 737c9dbe5643..afa09719336b 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;
+}