perf probe: Show correct statement line number by perf probe -l

The dwarf_getsrc_die() can return the line which is not a statement nor
the least line number among the lines which shares same address.

This can lead perf probe --list shows incorrect line number for probed
address.

To fix this, this introduces cu_getsrc_die() which returns only a
statement line and which is the least line number (we call it the
representive line for an address), and use it in cu_find_lineinfo().

Also, if the given address is the entry address of a real function,
cu_find_lineinfo() returns the function declared line number instead of
the start line number of the function body.

For example, without this change perf probe -l shows incorrect line as
below.

  # perf probe -a kernel_read:2
  Added new event:
    probe:kernel_read    (on kernel_read:2)

  You can now use it in all perf tools, such as:

  	perf record -e probe:kernel_read -aR sleep 1

  # perf probe -l
    probe:kernel_read    (on kernel_read:1@linux-5.0.0/fs/read_write.c)

With this fix, it shows correct line number as below;

  # perf probe -l
    probe:kernel_read    (on kernel_read:2@linux-5.0.0/fs/read_write.c)

Reported-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Ravi Bangoria <ravi.bangoria@linux.ibm.com>
Cc: Steven Rostedt (VMware) <rostedt@goodmis.org>
Cc: Tom Zanussi <tom.zanussi@linux.intel.com>
Link: http://lore.kernel.org/lkml/157406471067.24476.17463149618465494448.stgit@devnote2
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

diff --git a/tools/perf/util/dwarf-aux.c b/tools/perf/util/dwarf-aux.c
index 5544bfb..aa89801 100644 (file)
--- a/tools/perf/util/dwarf-aux.c
+++ b/tools/perf/util/dwarf-aux.c
@@ -59,6 +59,51 @@ const char *cu_get_comp_dir(Dwarf_Die *cu_die)
        return dwarf_formstring(&attr);
 }
 
+/* Unlike dwarf_getsrc_die(), cu_getsrc_die() only returns statement line */
+static Dwarf_Line *cu_getsrc_die(Dwarf_Die *cu_die, Dwarf_Addr addr)
+{
+       Dwarf_Addr laddr;
+       Dwarf_Lines *lines;
+       Dwarf_Line *line;
+       size_t nlines, l, u, n;
+       bool flag;
+
+       if (dwarf_getsrclines(cu_die, &lines, &nlines) != 0 ||
+           nlines == 0)
+               return NULL;
+
+       /* Lines are sorted by address, use binary search */
+       l = 0; u = nlines - 1;
+       while (l < u) {
+               n = u - (u - l) / 2;
+               line = dwarf_onesrcline(lines, n);
+               if (!line || dwarf_lineaddr(line, &laddr) != 0)
+                       return NULL;
+               if (addr < laddr)
+                       u = n - 1;
+               else
+                       l = n;
+       }
+       /* Going backward to find the lowest line */
+       do {
+               line = dwarf_onesrcline(lines, --l);
+               if (!line || dwarf_lineaddr(line, &laddr) != 0)
+                       return NULL;
+       } while (laddr == addr);
+       l++;
+       /* Going foward to find the statement line */
+       do {
+               line = dwarf_onesrcline(lines, l++);
+               if (!line || dwarf_lineaddr(line, &laddr) != 0 ||
+                   dwarf_linebeginstatement(line, &flag) != 0)
+                       return NULL;
+               if (laddr > addr)
+                       return NULL;
+       } while (!flag);
+
+       return line;
+}
+
 /**
  * cu_find_lineinfo - Get a line number and file name for given address
  * @cu_die: a CU DIE
@@ -72,17 +117,26 @@ int cu_find_lineinfo(Dwarf_Die *cu_die, unsigned long addr,
                    const char **fname, int *lineno)
 {
        Dwarf_Line *line;
-       Dwarf_Addr laddr;
+       Dwarf_Die die_mem;
+       Dwarf_Addr faddr;
 
-       line = dwarf_getsrc_die(cu_die, (Dwarf_Addr)addr);
-       if (line && dwarf_lineaddr(line, &laddr) == 0 &&
-           addr == (unsigned long)laddr && dwarf_lineno(line, lineno) == 0) {
+       if (die_find_realfunc(cu_die, (Dwarf_Addr)addr, &die_mem)
+           && die_entrypc(&die_mem, &faddr) == 0 &&
+           faddr == addr) {
+               *fname = dwarf_decl_file(&die_mem);
+               dwarf_decl_line(&die_mem, lineno);
+               goto out;
+       }
+
+       line = cu_getsrc_die(cu_die, (Dwarf_Addr)addr);
+       if (line && dwarf_lineno(line, lineno) == 0) {
                *fname = dwarf_linesrc(line, NULL, NULL);
                if (!*fname)
                        /* line number is useless without filename */
                        *lineno = 0;
        }
 
+out:
        return *lineno ?: -ENOENT;
 }