1 files changed, 53 insertions, 9 deletions

diff --git a/malloc/mtrace-ctl.c b/malloc/mtrace-ctl.c
index 2acc8976ce..641a6a2aff 100644
--- a/malloc/mtrace-ctl.c
+++ b/malloc/mtrace-ctl.c
@@ -1,19 +1,49 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <stdint.h>
+#include <string.h>
 #include <unistd.h>
+#include <sys/mman.h>
+
+/* Build like this:
+
+   gcc -shared -fpic mtrace-ctl.c -o /tmp/mtrace-ctl.so ../../glibc.build/libc.so
+
+   Invoke like this:
+
+   LD_PRELOAD=/tmp/mtrace-ctl.so ./myprog
+
+*/
 
 #include "mtrace.h"
 
+static void
+err(const char *str)
+{
+  write (2, str, strlen(str));
+  write (2, "\n", 1);
+  exit(1);
+}
+
 void __attribute__((constructor))
 djmain()
 {
-  char *e = getenv("MTRACE_CTL");
-  if (!e) e = "1000";
-  int sz = atoi(e) * sizeof(struct __malloc_trace_buffer_s);
-  char *buf = sbrk (sz+15);
-  while ((intptr_t)buf & 15)
-    buf ++;
+  char *e;
+  int sz;
+
+  e = getenv("MTRACE_CTL_COUNT");
+  if (!e)
+    e = "1000";
+  sz = atoi(e) * sizeof(struct __malloc_trace_buffer_s);
+
+  char *buf = mmap (NULL, sz, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+  if (!buf)
+    err("Cannot mmap");
+
+  buf[0] = 1;
+  buf[sz-1] = 1;
+
+  /* This must be the last thing we do.  */
   __malloc_set_trace_buffer ((void *)buf, sz);
   return;
 }
@@ -31,17 +61,29 @@ const char * const typenames[] = {
 void __attribute__((destructor))
 djend()
 {
+  char *e;
   FILE *outf;
   int head, size, i;
+
+  /* Prevent problems with recursion etc by shutting off trace right away.  */
   __malloc_trace_buffer_ptr buf = __malloc_get_trace_buffer (&size, &head);
-  outf = fopen("/tmp/mtrace.out", "w");
+  __malloc_set_trace_buffer (NULL, 0);
+
+  e = getenv("MTRACE_CTL_FILE");
+  if (!e)
+    e = "/tmp/mtrace.out";
+
+  outf = fopen(e, "w");
   if (!outf)
-    return;
+    err("cannot open output file");
+  setbuf (outf, NULL);
+
+  fprintf (outf, "%d out of %d events captured\n", head, size);
 
   fprintf (outf, "threadid type     path    ptr1             size             ptr2\n");
   for (i=0; i<size; i++)
     {
-      __malloc_trace_buffer_ptr t = buf + i % size;
+      __malloc_trace_buffer_ptr t = buf + (i+head) % size;
 
       switch (t->type)
 	{
@@ -65,5 +107,7 @@ djend()
 	}
     }
   fclose (outf);
+
+  munmap (buf, size * sizeof(struct __malloc_trace_buffer_s));
   return;
 }