linux-kernel - [BUGFIX PATCH 3/3] perf/probe: Fix to show function entry line as probe-able

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Date:   Thu, 24 Oct 2019 18:12:54 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     Jiri Olsa <jolsa@...hat.com>, Namhyung Kim <namhyung@...nel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        linux-kernel@...r.kernel.org
Subject: [BUGFIX PATCH 3/3] perf/probe: Fix to show function entry line as probe-able

Fix die_walk_lines() to list the function entry line correctly.
Since the dwarf_entrypc() does not return the entry pc if the DIE
has only range attribute, __die_walk_funclines() fails to list
the declaration line (entry line) in that case.

To solve this issue, this introduces die_entrypc() which correctly
returns the entry PC (the first address range) even if the DIE has
only range attribute. With this fix die_walk_lines() shows the
function entry line is able to probe correctly.

Fixes: 4cc9cec636e7 ("perf probe: Introduce lines walker interface")
Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org>
---
 tools/perf/util/dwarf-aux.c |   24 +++++++++++++++++++++++-
 tools/perf/util/dwarf-aux.h |    3 +++
 2 files changed, 26 insertions(+), 1 deletion(-)

diff --git a/tools/perf/util/dwarf-aux.c b/tools/perf/util/dwarf-aux.c
index 929b7c0567f4..063f71da6b63 100644
--- a/tools/perf/util/dwarf-aux.c
+++ b/tools/perf/util/dwarf-aux.c
@@ -307,6 +307,28 @@ bool die_is_func_def(Dwarf_Die *dw_die)
 		dwarf_attr(dw_die, DW_AT_declaration, &attr) == NULL);
 }
 
+/**
+ * die_entrypc - Returns entry PC (the lowest address) of a DIE
+ * @dw_die: a DIE
+ * @addr: where to store entry PC
+ *
+ * Since dwarf_entrypc() does not return entry PC if the DIE has only address
+ * range, we have to use this to retrieve the lowest address from the address
+ * range attribute.
+ */
+int die_entrypc(Dwarf_Die *dw_die, Dwarf_Addr *addr)
+{
+	Dwarf_Addr base, end;
+
+	if (!addr)
+		return -EINVAL;
+
+	if (dwarf_entrypc(dw_die, addr) == 0)
+		return 0;
+
+	return dwarf_ranges(dw_die, 0, &base, addr, &end) < 0 ? -ENOENT : 0;
+}
+
 /**
  * die_is_func_instance - Ensure that this DIE is an instance of a subprogram
  * @dw_die: a DIE
@@ -713,7 +735,7 @@ static int __die_walk_funclines(Dwarf_Die *sp_die, bool recursive,
 	/* Handle function declaration line */
 	fname = dwarf_decl_file(sp_die);
 	if (fname && dwarf_decl_line(sp_die, &lineno) == 0 &&
-	    dwarf_entrypc(sp_die, &addr) == 0) {
+	    die_entrypc(sp_die, &addr) == 0) {
 		lw.retval = callback(fname, lineno, addr, data);
 		if (lw.retval != 0)
 			goto done;
diff --git a/tools/perf/util/dwarf-aux.h b/tools/perf/util/dwarf-aux.h
index f204e5892403..506006e0cf66 100644
--- a/tools/perf/util/dwarf-aux.h
+++ b/tools/perf/util/dwarf-aux.h
@@ -29,6 +29,9 @@ int cu_walk_functions_at(Dwarf_Die *cu_die, Dwarf_Addr addr,
 /* Get DW_AT_linkage_name (should be NULL for C binary) */
 const char *die_get_linkage_name(Dwarf_Die *dw_die);
 
+/* Get the lowest PC in DIE (including range list) */
+int die_entrypc(Dwarf_Die *dw_die, Dwarf_Addr *addr);
+
 /* Ensure that this DIE is a subprogram and definition (not declaration) */
 bool die_is_func_def(Dwarf_Die *dw_die);