[PATCH v2 00/16] Interrupting programs that block/ignore SIGINT

[Pedro Alves <pedro@palves.net>]

New in v2:
  - run + detach no longer results in the detached process dying with
    SIGHUP.  GDB no longer queries about it on detach.
  - the testsuite gets fewer "tty /dev/tty" as a result.
  - documentation updated accordingly.
  - documentation now explicitly mentions that you can use "signal
    SIGINT" after Ctrl-C.
  - Added missing "@noindent" per Eli's review.
  - the gdb.base/annota1.exp patch has been meanwhile merged

For review convenience, I've put this in the users/palves/ctrl-c
branch.

Currently, on GNU/Linux, it is not possible to interrupt with Ctrl-C
programs that block or ignore SIGINT, with e.g., sigprocmask or
signal(SIGINT, SIG_IGN).  You type Ctrl-C, but nothing happens.

Similarly, if a program uses sigwait to wait for SIGINT, and the
program receives a SIGINT, the SIGINT is _not_ intercepted by ptrace,
it goes straight to the inferior.  These problems have been known for
years, and recorded in gdb/9425, gdb/14559.

This is a consequence of how GDB implements interrupting programs with
Ctrl-C -- when GDB spawns a new process, it makes the process use the
same terminal as GDB, and then makes the process's process group be
the foreground process group in GDB's terminal.  This means that when
the process is running in the foreground, after e.g. "continue", when
the user types Ctrl-C, the kernel sends a SIGINT to the foreground
process group, which is the inferior.  GDB then intercepts the SIGINT
via ptrace, the same way it intercepts any other signal, stops all the
other threads of the inferior if in all-stop, and presents the
"Program received SIGINT" stop to the user.

This series address the problem by turning Ctrl-C handling around such
that the SIGINT always reaches GDB first, not the inferior.  That is
done by making GDB put inferiors in their own terminal/session created
by GDB.  I.e., GDB creates a pseudo-terminal master/slave pair, makes
the inferior run with the slave as its terminal, and pumps
output/input on the master end.  Because the inferior is run with its
own session/terminal, GDB is free to remain as the foreground process
in its own terminal, which means that the Ctrl-C SIGINT always reaches
GDB first, instead of reaching the inferior first, and then GDB
reacting to the ptrace-intercepted SIGINT.  Because GDB gets the
SIGINT first, GDB is then free to handle it by interrupting the
program any way it sees fit.

The series will then make GDB interrupt the program with SIGSTOP
instead of SIGINT, which always works even if the inferior
blocks/ignores SIGINT -- SIGSTOP can't be ignored.  (In the future GDB
may even switch to PTRACE_INTERRUPT, though that's a project of its
own.)

Having the inferior in its own terminal also means that GDB is in
control of when inferior output is flushed to the screen.  When
debugging with the CLI, this means that inferior output is now never
interpersed with GDB's output in an unreadable fashion.  This will
also allow fixing the problem of inferior output really messing up the
screen in the TUI, forcing users to Ctrl-L to refresh the screen.
This series does not address the TUI part, but it shouldn't be too
hard -- I wrote a quick&dirty prototype patch doing that a few years
back, so I know it works.

Tested on GNU/Linux native, gdbserver and gdbserver + "maint target
set-non-stop on".  Also build-tested on mingw32-w64, Solaris 11, and
OpenBSD.

More details in each of the patches in the series.

The first patch adds tests that fail currently, but will pass at the
end of the series.

The main GDB changes are in patches #12 and #15.

Patch #1-#5, #9-#11, #13-#14 could go in without the main changes.

All documentation (manual, NEWS) is in the last patch -- patch #16.

Pedro Alves (16):
  Test interrupting programs that block SIGINT [gdb/9425, gdb/14559]
  prefork_hook: Remove 'args' parameter
  Make gdb.base/long-inferior-output.exp fail fast
  Fix gdb.multi/multi-term-settings.exp race
  Don't check parent pid in
    gdb.threads/{ia64-sigill,siginfo-threads,watchthreads-reorder}.c
  Special-case "set inferior-tty /dev/tty"
  Make inferior/GDB share terminal in tests expecting output after
    detach
  Make inferior/GDB share terminal in tests that exercise GDB/inferior
    reading same input
  gdb.mi/mi-logging.exp, don't send input to GDB while the inferior is
    running
  target_terminal::ours_for_output before printing signal received
  Move scoped_ignore_sigttou to gdbsupport/
  Always put inferiors in their own terminal/session [gdb/9425,
    gdb/14559]
  exists_non_stop_target: Avoid flushing frames
  convert previous_inferior_ptid to strong reference to thread_info
  GNU/Linux: Interrupt/Ctrl-C with SIGSTOP instead of SIGINT [PR
    gdb/9425, PR gdb/14559]
  Document pseudo-terminal and interrupting changes

 gdb/doc/gdb.texinfo                           | 117 ++-
 gdb/NEWS                                      |  23 +
 gdb/Makefile.in                               |   1 -
 gdb/event-top.c                               |  10 +-
 gdb/fork-child.c                              |  10 +-
 gdb/inf-ptrace.c                              |  24 +-
 gdb/inf-ptrace.h                              |   8 +
 gdb/infcmd.c                                  |  39 +-
 gdb/inferior.h                                |   4 +
 gdb/inflow.c                                  | 719 +++++++++++++++---
 gdb/infrun.c                                  | 179 ++++-
 gdb/infrun.h                                  |  16 +
 gdb/linux-nat.c                               | 115 ++-
 gdb/linux-nat.h                               |   2 +
 gdb/nat/fork-inferior.c                       | 120 ++-
 gdb/nat/fork-inferior.h                       |  30 +-
 gdb/procfs.c                                  |   1 -
 gdb/ser-unix.c                                |   2 +-
 gdb/target.c                                  |  40 +-
 gdb/terminal.h                                |   3 +
 .../gdb.base/annota-input-while-running.exp   |   4 +
 gdb/testsuite/gdb.base/annota1.exp            |   3 +-
 .../gdb.base/bp-cmds-continue-ctrl-c.exp      |   3 +
 .../gdb.base/continue-all-already-running.exp |   3 +
 gdb/testsuite/gdb.base/infcall-input.exp      |  12 +-
 .../gdb.base/interrupt-daemon-attach.exp      |   2 +-
 gdb/testsuite/gdb.base/interrupt-daemon.exp   |   4 +-
 gdb/testsuite/gdb.base/interrupt-noterm.exp   |   2 +-
 gdb/testsuite/gdb.base/interrupt.exp          |   4 +-
 .../gdb.base/long-inferior-output.exp         |  31 +-
 gdb/testsuite/gdb.base/random-signal.exp      |   3 +-
 gdb/testsuite/gdb.base/range-stepping.exp     |   2 +-
 gdb/testsuite/gdb.base/sigint-masked-out.c    |  43 ++
 gdb/testsuite/gdb.base/sigint-masked-out.exp  | 109 +++
 gdb/testsuite/gdb.base/sigint-sigwait.c       |  80 ++
 gdb/testsuite/gdb.base/sigint-sigwait.exp     | 113 +++
 gdb/testsuite/gdb.gdb/selftest.exp            |   4 +-
 gdb/testsuite/gdb.mi/mi-logging.exp           |  94 ++-
 gdb/testsuite/gdb.mi/new-ui-mi-sync.exp       |   2 +-
 .../gdb.multi/multi-target-interrupt.exp      |   2 +-
 .../gdb.multi/multi-target-no-resumed.exp     |   2 +-
 .../gdb.multi/multi-term-settings.exp         |  92 ++-
 gdb/testsuite/gdb.server/reconnect-ctrl-c.exp |   4 +-
 gdb/testsuite/gdb.threads/async.exp           |   2 +-
 .../gdb.threads/continue-pending-status.exp   |   2 +-
 gdb/testsuite/gdb.threads/ia64-sigill.c       |   5 -
 gdb/testsuite/gdb.threads/leader-exit.exp     |   2 +-
 gdb/testsuite/gdb.threads/manythreads.exp     |   4 +-
 .../process-dies-while-detaching.exp          |   3 +
 gdb/testsuite/gdb.threads/pthreads.exp        |   2 +-
 gdb/testsuite/gdb.threads/schedlock.exp       |  11 +-
 gdb/testsuite/gdb.threads/siginfo-threads.c   |   5 -
 gdb/testsuite/gdb.threads/sigthread.exp       |   2 +-
 .../gdb.threads/watchthreads-reorder.c        |   5 -
 gdb/testsuite/lib/gdb.exp                     |  19 +
 gdb/tui/tui-win.c                             |   3 +
 gdbserver/fork-child.cc                       |  15 +-
 gdbsupport/Makefile.am                        |   1 +
 gdbsupport/Makefile.in                        |  15 +-
 gdbsupport/managed-tty.cc                     |  22 +
 gdbsupport/managed-tty.h                      |  42 +
 .../scoped_ignore_sigttou.h                   |   8 +-
 62 files changed, 1994 insertions(+), 255 deletions(-)
 create mode 100644 gdb/testsuite/gdb.base/sigint-masked-out.c
 create mode 100644 gdb/testsuite/gdb.base/sigint-masked-out.exp
 create mode 100644 gdb/testsuite/gdb.base/sigint-sigwait.c
 create mode 100644 gdb/testsuite/gdb.base/sigint-sigwait.exp
 create mode 100644 gdbsupport/managed-tty.cc
 create mode 100644 gdbsupport/managed-tty.h
 rename gdb/inflow.h => gdbsupport/scoped_ignore_sigttou.h (90%)


base-commit: c9923e71ff57ce6e824833560aae59057c6f5783
-- 
2.26.2