[binutils-gdb] QUIT processing w/ explicit throw for gdb_exception_forced_quit

[binutils-gdb] QUIT processing w/ explicit throw for gdb_exception_forced_quit

[Kevin Buettner]

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=363429d593eb1eb17f3f2cf6c247f60fadf660d9

commit 363429d593eb1eb17f3f2cf6c247f60fadf660d9
Author: Kevin Buettner <kevinb@redhat.com>
Date:   Mon Feb 27 16:11:37 2023 -0700

    QUIT processing w/ explicit throw for gdb_exception_forced_quit
    
    This commit contains changes which have an explicit throw for
    gdb_exception_forced_quit, or, in a couple of cases for gdb_exception,
    but with a throw following a check to see if 'reason' is
    RETURN_FORCED_QUIT.
    
    Most of these are straightforward - it made sense to continue to allow
    an existing catch of gdb_exception to also catch gdb_exception_quit;
    in these cases, a catch/throw for gdb_exception_forced_quit was added.
    
    There are two cases, however, which deserve a more detailed
    explanation.
    
    1) remote_fileio_request in gdb/remote-fileio.c:
    
    The try block calls do_remote_fileio_request which can (in turn)
    call one of the functions in remote_fio_func_map[].  Taking the
    first one, remote_fileio_func_open(), we have the following call
    path to maybe_quit():
    
      remote_fileio_func_open(remote_target*, char*)
        -> target_read_memory(unsigned long, unsigned char*, long)
        -> target_read(target_ops*, target_object, char const*, unsigned char*, unsigned long, long)
        -> maybe_quit()
    
    Since there is a path to maybe_quit(), we must ensure that the
    catch block is not permitted to swallow a QUIT representing a
    SIGTERM.
    
    However, for this case, we must take care not to change the way that
    Ctrl-C / SIGINT is handled; we want to send a suitable EINTR reply to
    the remote target should that happen.  That being the case, I added a
    catch/throw for gdb_exception_forced_quit.  I also did a bit of
    rewriting here, adding a catch for gdb_exception_quit in favor of
    checking the 'reason' code in the catch block for gdb_exception.
    
    2) mi_execute_command in gdb/mi/mi-main.c:
    
    The try block calls captured_mi_execute_command(); there exists
    a call path to maybe_quit():
    
      captured_mi_execute_command(ui_out*, mi_parse*)
        -> mi_cmd_execute(mi_parse*)
        -> get_current_frame()
        -> get_prev_frame_always_1(frame_info*)
        -> frame_register_unwind_location(frame_info*, int, int*, lval_type*, unsigned long*, int*)
        -> frame_register_unwind(frame_info*, int, int*, int*, lval_type*, unsigned long*, int*, unsigned char*)
        -> value_entirely_available(value*)
        -> value_fetch_lazy(value*)
        -> value_fetch_lazy_memory(value*)
        -> read_value_memory(value*, long, int, unsigned long, unsigned char*, unsigned long)
        -> maybe_quit()
    
    That being the case, we can't allow the exception handler (catch block)
    to swallow a gdb_exception_quit for SIGTERM.  However, it does seem
    reasonable to output the exception via the mi interface so that some
    suitable message regarding SIGTERM might be printed; therefore, I
    check the exception's 'reason' field for RETURN_FORCED_QUIT and
    do a throw for this case.
    
    Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=26761
    Tested-by: Tom de Vries <tdevries@suse.de>
    Approved-By: Pedro Alves <pedro@palves.net>

Diff:
---
 gdb/event-top.c     |  2 ++
 gdb/mi/mi-main.c    |  4 ++++
 gdb/remote-fileio.c | 13 +++++++++----
 3 files changed, 15 insertions(+), 4 deletions(-)

diff --git a/gdb/event-top.c b/gdb/event-top.c
index f0a3f0d418c..36863292696 100644
--- a/gdb/event-top.c
+++ b/gdb/event-top.c
@@ -1281,6 +1281,8 @@ async_disconnect (gdb_client_data arg)
       gdb_puts ("Could not kill the program being debugged",
 		gdb_stderr);
       exception_print (gdb_stderr, exception);
+      if (exception.reason == RETURN_FORCED_QUIT)
+	throw;
     }
 
   for (inferior *inf : all_inferiors ())
diff --git a/gdb/mi/mi-main.c b/gdb/mi/mi-main.c
index 84a95a24684..0013e5dfafd 100644
--- a/gdb/mi/mi-main.c
+++ b/gdb/mi/mi-main.c
@@ -1952,6 +1952,10 @@ mi_execute_command (const char *cmd, int from_tty)
 	     somewhere.  */
 	  mi_print_exception (command->token, result);
 	  mi_out_rewind (current_uiout);
+
+	  /* Throw to a higher level catch for SIGTERM sent to GDB.  */
+	  if (result.reason == RETURN_FORCED_QUIT)
+	    throw;
 	}
 
       bpstat_do_actions ();
diff --git a/gdb/remote-fileio.c b/gdb/remote-fileio.c
index 3ff2a65b0ec..69b409708a3 100644
--- a/gdb/remote-fileio.c
+++ b/gdb/remote-fileio.c
@@ -1191,12 +1191,17 @@ remote_fileio_request (remote_target *remote, char *buf, int ctrlc_pending_p)
 	{
 	  do_remote_fileio_request (remote, buf);
 	}
+      catch (const gdb_exception_forced_quit &ex)
+	{
+	  throw;
+	}
+      catch (const gdb_exception_quit &ex)
+	{
+	  remote_fileio_reply (remote, -1, FILEIO_EINTR);
+	}
       catch (const gdb_exception &ex)
 	{
-	  if (ex.reason == RETURN_QUIT)
-	    remote_fileio_reply (remote, -1, FILEIO_EINTR);
-	  else
-	    remote_fileio_reply (remote, -1, FILEIO_EIO);
+	  remote_fileio_reply (remote, -1, FILEIO_EIO);
 	}
     }