From 74162906f3359f2b75b018ee0a2c39725306111f Mon Sep 17 00:00:00 2001
From: Alex Shinn <ashinn@users.noreply.github.com>
Date: Thu, 30 Jan 2014 22:18:23 +0900
Subject: [PATCH] Adding optional stack traces on potential GC misses detected
 by conservative tracing.

---
 gc.c                     | 13 +++++++++++++
 include/chibi/features.h | 12 ++++++++++++
 include/chibi/sexp.h     |  5 +++++
 sexp.c                   |  8 ++++++++
 4 files changed, 38 insertions(+)

diff --git a/gc.c b/gc.c
index eb68c300..9c49e01a 100644
--- a/gc.c
+++ b/gc.c
@@ -223,6 +223,18 @@ int stack_references_pointer_p (sexp ctx, sexp x) {
   return 0;
 }
 
+#if SEXP_USE_TRACK_ALLOC_BACKTRACE
+void sexp_print_gc_trace(sexp ctx, sexp p) {
+  int i;
+  char **debug_text = backtrace_symbols(p->backtrace, SEXP_BACKTRACE_SIZE);
+  for (i=0; i < SEXP_BACKTRACE_SIZE; i++)
+    fprintf(stderr, SEXP_BANNER("    : %s"), debug_text[i]);
+  free(debug_text);
+}
+#else
+#define sexp_print_gc_trace(ctx, p)
+#endif
+
 void sexp_conservative_mark (sexp ctx) {
   sexp_heap h = sexp_context_heap(ctx);
   sexp p, end;
@@ -247,6 +259,7 @@ void sexp_conservative_mark (sexp ctx) {
           if (p && sexp_pointerp(p)) {
             fprintf(stderr, SEXP_BANNER("MISS: %p [%d]: %s"), p,
                     sexp_pointer_tag(p), sexp_pointer_source(p));
+            sexp_print_gc_trace(ctx, p);
             fflush(stderr);
           }
 #endif
diff --git a/include/chibi/features.h b/include/chibi/features.h
index bfb6933a..25fa7c7c 100644
--- a/include/chibi/features.h
+++ b/include/chibi/features.h
@@ -87,6 +87,10 @@
 /* uncomment this to track what C source line each object is allocated from */
 /* #define SEXP_USE_TRACK_ALLOC_SOURCE 1 */
 
+/* uncomment this to take a short backtrace of where each object is */
+/* allocated from */
+/* #define SEXP_USE_TRACK_ALLOC_BACKTRACE 1 */
+
 /* uncomment this to add additional native gc checks to verify a magic header */
 /* #define SEXP_USE_HEADER_MAGIC 1 */
 
@@ -372,6 +376,14 @@
 #define SEXP_USE_TRACK_ALLOC_SOURCE SEXP_USE_DEBUG_GC > 2
 #endif
 
+#ifndef SEXP_USE_TRACK_ALLOC_BACKTRACE
+#define SEXP_USE_TRACK_ALLOC_BACKTRACE SEXP_USE_TRACK_ALLOC_SOURCE
+#endif
+
+#ifndef SEXP_BACKTRACE_SIZE
+#define SEXP_BACKTRACE_SIZE 3
+#endif
+
 #ifndef SEXP_USE_HEADER_MAGIC
 #define SEXP_USE_HEADER_MAGIC 0
 #endif
diff --git a/include/chibi/sexp.h b/include/chibi/sexp.h
index b4f5ad6e..c410c0dc 100755
--- a/include/chibi/sexp.h
+++ b/include/chibi/sexp.h
@@ -75,6 +75,10 @@ typedef unsigned long size_t;
 #endif
 #endif
 
+#if SEXP_USE_TRACK_ALLOC_BACKTRACE
+#include <execinfo.h>
+#endif
+
 #include <ctype.h>
 #include <stdio.h>
 
@@ -294,6 +298,7 @@ struct sexp_struct {
   unsigned int syntacticp:1;
 #if SEXP_USE_TRACK_ALLOC_SOURCE
   const char* source;
+  void* backtrace[SEXP_BACKTRACE_SIZE];
 #endif
 #if SEXP_USE_HEADER_MAGIC
   unsigned int magic;
diff --git a/sexp.c b/sexp.c
index b5dcea02..03ad1834 100644
--- a/sexp.c
+++ b/sexp.c
@@ -62,11 +62,19 @@ sexp sexp_push_op(sexp ctx, sexp* loc, sexp x) {
 #endif
 
 sexp sexp_alloc_tagged_aux(sexp ctx, size_t size, sexp_uint_t tag sexp_current_source_param) {
+#if SEXP_USE_TRACK_ALLOC_BACKTRACE
+  int i;
+  void* trace[SEXP_BACKTRACE_SIZE + 1];
+#endif
   sexp res = (sexp) sexp_alloc(ctx, size);
   if (res && ! sexp_exceptionp(res)) {
     sexp_pointer_tag(res) = tag;
 #if SEXP_USE_TRACK_ALLOC_SOURCE
     sexp_pointer_source(res) = source;
+#if SEXP_USE_TRACK_ALLOC_BACKTRACE
+    backtrace(trace, SEXP_BACKTRACE_SIZE + 1);
+    for (i=0; i<SEXP_BACKTRACE_SIZE; i++) res->backtrace[i] = trace[i+1];
+#endif
 #endif
 #if SEXP_USE_HEADER_MAGIC
     sexp_pointer_magic(res) = SEXP_POINTER_MAGIC;