We have places where we call a blocking gdb_select expecting that a
Ctrl-C will unblock it. However, if the Ctrl-C is pressed just before
gdb_select, the SIGINT handler runs before gdb_select, and thus
gdb_select won't return.
For example gdb_readline_no_editing:
QUIT;
/* Wait until at least one byte of data is available. Control-C
can interrupt gdb_select, but not fgetc. */
FD_ZERO (&readfds);
FD_SET (fd, &readfds);
if (gdb_select (fd + 1, &readfds, NULL, NULL, NULL) == -1)
and stdio_file_read:
/* For the benefit of Windows, call gdb_select before reading from
the file. Wait until at least one byte of data is available.
Control-C can interrupt gdb_select, but not read. */
{
fd_set readfds;
FD_ZERO (&readfds);
FD_SET (stdio->fd, &readfds);
if (gdb_select (stdio->fd + 1, &readfds, NULL, NULL, NULL) == -1)
return -1;
}
return read (stdio->fd, buf, length_buf);
This is a race classically fixed with either the self-pipe trick, or
by blocking SIGINT and then using pselect instead of select.
Blocking SIGINT most of the time would mean that check_quit_flag (and
thus QUIT) would need to do a syscall every time it is called, which
sounds best avoided, since QUIT is called in many loops. Thus we take
the self-pipe trick route (wrapped in a serial event).
Instead of having all places that need this manually add an extra file
descriptor to the set of gdb_select's watched file descriptors, we
introduce a wrapper, interruptible_select, that does that.
The Windows version of gdb_select actually does not suffer from this,
because mingw-hdep.c:gdb_call_async_signal_handler sets a Windows
event that gdb_select always waits on. So this patch can be seen as
generalization of that technique. We can't remove that extra event
from mingw-hdep.c until we get rid of immediate_quit though.
gdb/ChangeLog:
2016-04-12 Pedro Alves <palves@redhat.com>
* defs.h: Extend QUIT-related comments to mention
interruptible_select.
(quit_serial_event_set, quit_serial_event_clear): Declare.
* event-top.c: Include "ser-event.h" and "gdb_select.h".
(quit_serial_event): New global.
(async_init_signals): Make quit_serial_event.
(quit_serial_event_set, quit_serial_event_clear)
(quit_serial_event_fd, interruptible_select): New functions.
* extension.c (set_quit_flag): Set the quit serial event.
(check_quit_flag): Clear the quit serial event.
* gdb_select.h (interruptible_select): New declaration.
* guile/scm-ports.c (ioscm_input_waiting): Use
interruptible_select instead of gdb_select.
* top.c (gdb_readline_no_editing): Likewise.
* ui-file.c (stdio_file_read): Likewise.
After the last gnulib import (Dec 2012), gnulib upstream started
replacing mingw's 'struct timeval' with a version with 64-bit time_t,
for POSIX compliance:
commit f8e84098084b3b53bc6943a5542af1f607ffd477
Author: Bruno Haible <bruno@clisp.org>
Date: Sat Jan 28 18:12:10 2012 +0100
sys_time: Override 'struct timeval' on some native Windows platforms.
See:
https://lists.gnu.org/archive/html/bug-gnulib/2012-01/msg00372.html
However, that results in conflicts with native Winsock2's 'select':
select()'s argument
http://sourceforge.net/p/mingw-w64/mailman/message/29610438/
... and libiberty's timeval-utils.h timeval_add/timeval_sub, at the
least.
We don't really need the POSIX compliance, so this patch prepares us
to simply not use gnulib's 'struct timeval' replacement once a more
recent gnulib is imported, thus preserving the current behavior, by
adding a sys/time.h wrapper header that undefs gnulib's replacements,
and including that everywhere instead.
The SIZE -> OSIZE change is necessary because newer gnulib's
sys/time.h also includes windows.h/winsock2.h, which defines a
conflicting SIZE symbol.
Cross build-tested mingw-w64 32-bit and 64-bit.
Regtested on x86_64 Fedora 20.
gdb/ChangeLog:
2015-08-24 Pedro Alves <palves@redhat.com>
* Makefile.in (HFILES_NO_SRCDIR): Add common/gdb_sys_time.h.
* common/gdb_sys_time.h: New file.
* event-loop.c: Include gdb_sys_time.h instead of sys/time.h.
* gdb_select.h: Likewise.
* gdb_usleep.c: Likewise.
* maint.c: Likewise.
* mi/mi-main.c: Likewise.
* mi/mi-parse.h: Likewise.
* remote-fileio.c: Likewise.
* remote-m32r-sdi.c: Likewise.
* remote.c: Likewise.
* ser-base.c: Likewise.
* ser-pipe.c: Likewise.
* ser-tcp.c: Likewise.
* ser-unix.c: Likewise.
* symfile.c: Likewise.
* symfile.c: Likewise. Rename OSIZE to SIZE throughout.
* target-memory.c: Include gdb_sys_time.h instead of sys/time.h.
* utils.c: Likewise.
gdb/gdbserver/ChangeLog:
2015-08-24 Pedro Alves <palves@redhat.com>
* debug.c: Include gdb_sys_time.h instead of sys/time.h.
* event-loop.c: Likewise.
* remote-utils.c: Likewise.
* tracepoint.c: Likewise.
Two modifications:
1. The addition of 2013 to the copyright year range for every file;
2. The use of a single year range, instead of potentially multiple
year ranges, as approved by the FSF.
call.
* cp-name-parser.y: Include "config.h".
* xml-tdesc.c (fetch_xml_from_file): Properly cast sentinel in
concat call.
* gdb_select.h: Include sys/time.h if sys/select.h is not
available.
* Makefile.in (gdb_select_h, ser_tcp_h): New.
(ALLDEPFILES): Add ser-mingw.c.
(event-loop.o, inflow.o, mingw-hdep.o, posix-hdep.o, ser-base.o)
(ser-tcp.o, ser-unix.o): Update.
(ser-mingw.o): New rule.
* configure: Regenerated.
* configure.ac: Add ser-mingw.o for mingw32.
* ser-mingw.c: New file.
* event-loop.c: Include "gdb_select.h".
(gdb_select): Remove, moved to mingw-hdep.c and posix-hdep.c.
* ser-base.c: Include "gdb_select.h".
(ser_base_wait_for): Use gdb_select.
* serial.c (serial_for_fd): New function.
(serial_fdopen): Try "terminal" before "hardwire". Initialize
the allocated struct serial.
(serial_wait_handle): New function.
* serial.h (serial_for_fd, serial_wait_handle): New prototypes.
(struct serial_ops) [USE_WIN32API]: Add wait_handle.
* gdb_select.h: New file.
* ser-tcp.c: Include "ser-tcp.h". Remove unused "ser-unix.h" include.
(net_close, net_read_prim, net_write_prim): Make global.
(net_open): Likewise. Pass an exception set to select. Whitespace fix.
Document why we can not use gdb_select.
(_initialize_ser_tcp) [USE_WIN32API]: Do not register TCP support here.
* ser-tcp.h: New file.
* inflow.c (gdb_has_a_terminal): Don't initialize stdin_serial here.
(handle_sigio): Use gdb_select.
(initialize_stdin_serial): New function.
* terminal.h (initialize_stdin_serial): New prototype.
* top.c (gdb_init): Call initialize_stdin_serial.
* mingw-hdep.c (gdb_select): New function, moved from gdb_select in
event-loop.c. Add exception condition support. Use serial_for_fd
and serial_wait_handle. Fix timeout handling.
* posix-hdep.c: Include "gdb_select.h".
(gdb_select): New function.
* remote-st.c (connect_command): Use gdb_select.
* ser-unix.c: Include "gdb_select.h".
(hardwire_send_break, wait_for): Use gdb_select.
Pedro Alves