common: make model_print() use OS file descriptor, not C library FILE*

A C library FILE does buffering (and possibly other opaque operations)
that can conflict with the model-checker's methods of snapshotting
memory. Particularly, it seems like we could corrupt and drop data that
was written to model_out, if the data was large enough and buffered in
just the right way.

Really, with the presence of dprintf(), there is no reason to print to a
FILE stream; we can just use the file descriptor (either STDOUT_FILENO
or the descriptor received from dup2()).

This fixes bugs seen in verbose mode, with a lot of extra debug
printing. Some of the output was being dropped.

diff --git a/common.cc b/common.cc
index b71c00ab804e5a7b1817790ac825791761b8f0d8..a43064d527a03340d0f62d260b13b7638cf131f5 100644 (file)
--- a/common.cc
+++ b/common.cc
@@ -14,15 +14,17 @@
 
 #define MAX_TRACE_LEN 100
 
-/** @brief Model-checker output stream; default to stdout until redirected */
-FILE *model_out = stdout;
+/** @brief Model-checker output file descriptor; default to stdout until redirected */
+int model_out = STDOUT_FILENO;
 
 #define CONFIG_STACKTRACE
 /** Print a backtrace of the current program state. */
 void print_trace(void)
 {
 #ifdef CONFIG_STACKTRACE
-       print_stacktrace(model_out);
+       FILE *file = fdopen(model_out, "w");
+       print_stacktrace(file);
+       fclose(file);
 #else
        void *array[MAX_TRACE_LEN];
        char **strings;
@@ -69,7 +71,7 @@ static int fd_user_out; /**< @brief File descriptor from which to read user prog
  *
  * Redirects user program's stdout to a pipe so that we can dump it
  * selectively, when displaying bugs, etc.
- * Also connects a special file 'model_out' directly to stdout, for printing
+ * Also connects a file descriptor 'model_out' directly to stdout, for printing
  * data when needed.
  *
  * The model-checker can selectively choose to print/hide the user program
@@ -89,8 +91,7 @@ void redirect_output()
        int fd;
 
        /* Save stdout for later use */
-       fd = dup(fileno(stdout));
-       model_out = fdopen(fd, "w");
+       model_out = dup(fileno(stdout));
 
        /* Redirect program output to a pipe */
        int pipefd[2];
@@ -149,16 +150,15 @@ void print_program_output()
        fflush(stdout);
 
        /* Read program output pipe and write to (real) stdout */
-       int ret;
+       ssize_t ret;
        while (1) {
                ret = read_to_buf(fd_user_out, buf, sizeof(buf));
                if (!ret)
                        break;
                while (ret > 0) {
-                       int res = fwrite(buf, 1, ret, model_out);
+                       ssize_t res = write(model_out, buf, ret);
                        if (res < 0) {
-                               errno = ferror(model_out);
-                               perror("fwrite");
+                               perror("write");
                                exit(EXIT_FAILURE);
                        }
                        ret -= res;

diff --git a/common.h b/common.h
index c861285a8ab12c3c73720e357679ec84d4bc8269..1071135892ac11508c52459eee99e8d8da3ab254 100644 (file)
--- a/common.h
+++ b/common.h
@@ -8,9 +8,9 @@
 #include <stdio.h>
 #include "config.h"
 
-extern FILE *model_out;
+extern int model_out;
 
-#define model_print(fmt, ...) do { fprintf(model_out, fmt, ##__VA_ARGS__); } while (0)
+#define model_print(fmt, ...) do { dprintf(model_out, fmt, ##__VA_ARGS__); } while (0)
 
 #ifdef CONFIG_DEBUG
 #define DEBUG(fmt, ...) do { model_print("*** %15s:%-4d %25s() *** " fmt, __FILE__, __LINE__, __func__, ##__VA_ARGS__); } while (0)

diff --git a/model.cc b/model.cc
index b93653becc41d7acf250d7ff1153490fad056d69..f385e560f085cc9af3aec101207f732a7a3ef8e3 100644 (file)
--- a/model.cc
+++ b/model.cc
@@ -154,9 +154,6 @@ void ModelChecker::reset_to_initial_state()
        DEBUG("+++ Resetting to initial state +++\n");
        node_stack->reset_execution();
 
-       /* Print all model-checker output before rollback */
-       fflush(model_out);
-
        /**
         * FIXME: if we utilize partial rollback, we will need to free only
         * those pending actions which were NOT pending before the rollback