[PATCH] Avoid potencially-stale errno usage (was: Re: Include putpkt in TRY_CATCH. PR gdb/15275)

[Pedro Alves <palves at redhat dot com>]

On 03/28/2013 05:07 PM, Pedro Alves wrote:
> (
> There's a latent bug in the patch that that throw_perror_with_name
> call assumes error is still set to the right error, although
> remote_unpush_target is called in between.  I'm copying this
> from preexisting code, and we can fix both at once.)
> 
>   if (serial_write (remote_desc, str, len))
>     {
>       remote_unpush_target ();
>       throw_perror_with_name (TARGET_CLOSE_ERROR,
> )

Fixing this before it ends up forgotten and bites us at some
point.

Comments?

------------
Avoid potencially-stale errno usage.

The current throw_perror_with_name/TARGET_CLOSE_ERROR calls assume
errno is still set to the right error, although remote_unpush_target
is called in between, which may well change errno.

Tested on x86_64 Fedora 17 w/ gdbserver.

gdb/
2013-04-08  Pedro Alves  <palves@redhat.com>

	* remote.c (unpush_and_perror): New function.
	(readchar, remote_serial_write): Use it.

---

 gdb/remote.c |   32 ++++++++++++++++++++++----------
 1 file changed, 22 insertions(+), 10 deletions(-)

diff --git a/gdb/remote.c b/gdb/remote.c
index 740324b..e60ff78 100644
--- a/gdb/remote.c
+++ b/gdb/remote.c
@@ -7033,6 +7033,23 @@ remote_files_info (struct target_ops *ignore)
 /* Stuff for dealing with the packets which are part of this protocol.
    See comment at top of file for details.  */
 
+/* Close/unpush the remote target, and throw a TARGET_CLOSE_ERROR
+   error to higher layers.  Called when a serial error is detected.
+   The exception message is STRING, followed by a colon and a blank,
+   then the system error message for errno at function entry.  */
+
+static void
+unpush_and_perror (const char *string)
+{
+  char *errstr;
+
+  errstr = xstrprintf ("%s: %s", string, safe_strerror (errno));
+  make_cleanup (xfree, errstr);
+
+  remote_unpush_target ();
+  throw_error (TARGET_CLOSE_ERROR, "%s", errstr);
+}
+
 /* Read a single character from the remote end.  */
 
 static int
@@ -7048,14 +7065,11 @@ readchar (int timeout)
   switch ((enum serial_rc) ch)
     {
     case SERIAL_EOF:
-      remote_unpush_target ();
-      throw_error (TARGET_CLOSE_ERROR, _("Remote connection closed"));
+      unpush_and_perror (_("Remote connection closed"));
       /* no return */
     case SERIAL_ERROR:
-      remote_unpush_target ();
-      throw_perror_with_name (TARGET_CLOSE_ERROR,
-			      _("Remote communication error.  "
-				"Target disconnected."));
+      unpush_and_perror (_("Remote communication error.  "
+			   "Target disconnected."));
       /* no return */
     case SERIAL_TIMEOUT:
       break;
@@ -7071,10 +7085,8 @@ remote_serial_write (const char *str, int len)
 {
   if (serial_write (remote_desc, str, len))
     {
-      remote_unpush_target ();
-      throw_perror_with_name (TARGET_CLOSE_ERROR,
-			      _("Remote communication error.  "
-				"Target disconnected."));
+      unpush_and_perror (_("Remote communication error.  "
+			   "Target disconnected."));
     }
 }