perf script brstackinsn: Fix recovery from LBR/binary mismatch

BugLink: https://bugs.launchpad.net/bugs/1852492
[ Upstream commit e98df280bc2a499fd41d7f9e2d6733884de69902 ]

When the LBR data and the instructions in a binary do not match the loop
printing instructions could get confused and print a long stream of
bogus <bad> instructions.

The problem was that if the instruction decoder cannot decode an
instruction it ilen wasn't initialized, so the loop going through the
basic block would continue with the previous value.

Harden the code to avoid such problems:

- Make sure ilen is always freshly initialized and is 0 for bad
  instructions.

- Do not overrun the code buffer while printing instructions

- Print a warning message if the final jump is not on an instruction
  boundary.

Signed-off-by: Andi Kleen <ak@linux.intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Link: http://lore.kernel.org/lkml/20190927233546.11533-1-andi@firstfloor.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

diff --git a/tools/perf/builtin-script.c b/tools/perf/builtin-script.c
index 68aa2c8de5fa88d65eceda939173b1eb8479e92c..a3e0cdf69d37991a9ed98d45914f4777562e3e54 100644 (file)
--- a/tools/perf/builtin-script.c
+++ b/tools/perf/builtin-script.c
@@ -966,7 +966,7 @@ static int perf_sample__fprintf_brstackinsn(struct perf_sample *sample,
                        continue;
 
                insn = 0;
-               for (off = 0;; off += ilen) {
+               for (off = 0; off < (unsigned)len; off += ilen) {
                        uint64_t ip = start + off;
 
                        printed += ip__fprintf_sym(ip, thread, x.cpumode, x.cpu, &lastsym, attr, fp);
@@ -974,6 +974,7 @@ static int perf_sample__fprintf_brstackinsn(struct perf_sample *sample,
                                printed += ip__fprintf_jump(ip, &br->entries[i], &x, buffer + off, len - off, insn, fp);
                                break;
                        } else {
+                               ilen = 0;
                                printed += fprintf(fp, "\t%016" PRIx64 "\t%s\n", ip,
                                                   dump_insn(&x, ip, buffer + off, len - off, &ilen));
                                if (ilen == 0)
@@ -981,6 +982,8 @@ static int perf_sample__fprintf_brstackinsn(struct perf_sample *sample,
                                insn++;
                        }
                }
+               if (off != (unsigned)len)
+                       printed += fprintf(fp, "\tmismatch of LBR data and executable\n");
        }
 
        /*
@@ -1011,6 +1014,7 @@ static int perf_sample__fprintf_brstackinsn(struct perf_sample *sample,
                goto out;
        }
        for (off = 0; off <= end - start; off += ilen) {
+               ilen = 0;
                printed += fprintf(fp, "\t%016" PRIx64 "\t%s\n", start + off,
                                   dump_insn(&x, start + off, buffer + off, len - off, &ilen));
                if (ilen == 0)