From f1eb3aea114cbd1e2622cbe9618571f3e1eec115 Mon Sep 17 00:00:00 2001
From: Kouhei Sutou <kou@clear-code.com>
Date: Sun, 6 Mar 2016 11:58:54 +0900
Subject: Fix segmentation fault by backtrace and GC

GitHub: fix #3122

It reverts #3126. #3126 fixes the segmentation fault but generates
broken backtrace.

This change fixes the segmentation fault and generates correct
backtrace. The strategy of this change is "generating backtrace while
irep is alive".

/tmp/test.rb:
    def gen
      e0 = nil
      begin
        1.times {
          raise 'foobar'
        }
      rescue => e
        e0 = e
      end
      e0
    end

    e = gen
    GC.start
    gen
    GC.start

    puts e.backtrace.join("\n")

Run:

    % bin/mruby /tmp/test.rb
    /tmp/test.rb:5:in Object.gen
    /home/kou/work/ruby/mruby.kou/mrblib/numeric.rb:77:in Integral#times
    /tmp/test.rb:4:in Object.gen
    /tmp/test.rb:13

FYI:

    % ruby -v /tmp/test.rb
    ruby 2.3.0p0 (2015-12-25) [x86_64-linux-gnu]
    /tmp/test.rb:5:in `block in gen'
    /tmp/test.rb:4:in `times'
    /tmp/test.rb:4:in `gen'
    /tmp/test.rb:13:in `<main>'
---
 src/error.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

(limited to 'src/error.c')

diff --git a/src/error.c b/src/error.c
index 14e4ab4d3..13032b136 100644
--- a/src/error.c
+++ b/src/error.c
@@ -255,17 +255,22 @@ mrb_exc_set(mrb_state *mrb, mrb_value exc)
 {
   if (!mrb->gc.out_of_memory && mrb->backtrace.n > 0) {
     mrb_value target_exc = mrb_nil_value();
+    int ai;
+
+    ai = mrb_gc_arena_save(mrb);
     if ((mrb->exc && !have_backtrace(mrb, mrb->exc))) {
       target_exc = mrb_obj_value(mrb->exc);
     }
-    else if (!mrb_nil_p(exc) && mrb_obj_ptr(exc) == mrb->backtrace.exc) {
-      target_exc = exc;
+    else if (!mrb_nil_p(exc) && mrb->backtrace.exc) {
+      target_exc = mrb_obj_value(mrb->backtrace.exc);
+      mrb_gc_protect(mrb, target_exc);
     }
     if (!mrb_nil_p(target_exc)) {
       mrb_value backtrace;
       backtrace = mrb_restore_backtrace(mrb);
       set_backtrace(mrb, target_exc, backtrace);
     }
+    mrb_gc_arena_restore(mrb, ai);
   }
 
   mrb->backtrace.n = 0;
-- 
cgit v1.2.3