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Re: [RFC] PTRACE_ATTACH problem on new Linux kernels
Andrew Cagney writes:
> > Andrew Cagney writes:
> > > Solution 0 is to discard the STOP in infrun.c as part of the stop
> > > analyzis.
> > >
> >
> > Yes, but I am not sure it won't break the other cases that share that
> > stop analysis. The stop_soon_quietly variable is relied upon in other
> > places, like the start_remote function, the startup_inferior function,
> > the sharedlib machinery. That's why I thought the handling it in the
> > attach command would be safer.
>
> It certainly doesn't break anything, however, it also makes the long
> term problem harder.
>
> > > > A first solution could be that upon continuing, gdb never sends a
> > > > SIGSTOP through the ptrace call. I.e. the stop_signal in
> > > > ptrace(PTRACE_CONT, pid, stop_signal) could be changed to
> > > > TARGET_SIGNAL_0 if it is TARGET_SIGNAL_STOP (such a call is in
> > > > proceed(), and we already do some signal munging there).
> > > >
> > > > Another solution is to throw away the TARGET_SIGNAL_STOP that is saved
> > > > in stop_signal when we do an attach. This would be in
> > > > attach_command(), in infcmd.c. This way it would not come into play at
> > > > all at the next continue.
> > >
> > > This will make the desperatly needed objective of trying to eliminate
> > > the global stop_signal variable just that bit more difficult.
> > >
> > > If the already nasty hacks in HP/PA and solib code is ignored, the
> > > only places stop_signal is modified is in infrun.c.
> > >
> >
> > Hmm true, sigh.
>
> Think about the frames code where things got so complicated that no one
> was game to change it.
> With the changes in place I'm now finding my self fighting a rear-guard
> action to stop the old hacks re-appearing.
>
> > > > Yet another solution is that we 'hide' the TARGET_SIGNAL_STOP in
> > > > child_resume(), in i386-linux-nat.c but this would not be applicable
> > > > to the other linux arches.
> > >
> > > Or discard the signal in resume()?
> > >
> >
> > yes, proceed() already does something like that, but that would mean
> > that we modify the signal before doing the continue, and not after we
> > receive it. There is a lot that can happen between issuing an
> > 'attach' command, and a later 'continue'. Maybe we would be discarding
> > a valid SIGSTOP to pass to the inferior.
> >
> > I think the only option left is to change the handle_inferior_event
> > stop analysis, which is scary...
>
> Conceptually, the code is being used as:
>
> - connect to target
> - force the WFI state machine into a specific initial state (stop
> normally, stop_soon_quietly or, now, stop_soon_with_sigstop) (yes, ok,
> no one believes me when I say that WFI is a state machine :-)
> - run the WFI state machine to analize the target's state
>
> Can stop_soon_quietly be [ab]used / extended to in a more general way
> force WFI into other states? Either by treating it as bit fields or as
> alternative states? e.g.,
>
> enum stop_soon { stop_soon_normally, stop_soon_quietly,
> stop_soon_suspended };
>
> or struct stop_soon { int quietly; int suspended; }
>
> or ...
>
> Andrew
>
>
Kind of. I am testing the following:
2003-02-18 Elena Zannoni <ezannoni@redhat.com>
* infrun.c (stop_soon_quietly): Make it an enum, to better
override the default behavior of handle_inferior_event.
(clear_proceed_status): Update uses of stop_soon_quietly to
reflect that it is now an enum.
(start_remote): Ditto.
(handle_inferior_event): Change logic a bit if stop_soon_quietly
is set to handle the new kernel behavior for attach/sigstop.
Update uses of stop_soon_quietly.
* inferior.h (enum stop_kind): New enum.
* infcmd.c (attach_command): Use STOP_QUIETLY_NO_SIGSTOP.
Reset normal handle_inferior_event behavior, afterwards.
* fork-child.c (startup_inferior): Update.
* alpha-tdep.c (heuristic_proc_start): Update.
* solib-svr4.c (svr4_solib_create_inferior_hook): Update.
* solib-sunos.c (sunos_solib_create_inferior_hook): Update.
* solib-osf.c (osf_solib_create_inferior_hook): Update.
* solib-irix.c (irix_solib_create_inferior_hook): Update.
* remote-vx.c (vx_create_inferior): Update.
* mips-tdep.c (heuristic_proc_start): Update.
Index: alpha-tdep.c
===================================================================
RCS file: /cvs/uberbaum/gdb/alpha-tdep.c,v
retrieving revision 1.60
diff -u -p -r1.60 alpha-tdep.c
--- alpha-tdep.c 31 Jan 2003 18:28:25 -0000 1.60
+++ alpha-tdep.c 18 Feb 2003 20:24:34 -0000
@@ -564,7 +564,7 @@ heuristic_proc_start (CORE_ADDR pc)
stop_soon_quietly, but with this test, at least we
don't print out warnings for every child forked (eg, on
decstation). 22apr93 rich@cygnus.com. */
- if (!stop_soon_quietly)
+ if (stop_soon_quietly == NO_STOP_QUIETLY)
{
static int blurb_printed = 0;
Index: fork-child.c
===================================================================
RCS file: /cvs/uberbaum/gdb/fork-child.c,v
retrieving revision 1.18
diff -u -p -r1.18 fork-child.c
--- fork-child.c 16 Nov 2002 19:23:52 -0000 1.18
+++ fork-child.c 18 Feb 2003 20:24:35 -0000
@@ -409,7 +409,8 @@ startup_inferior (int ntraps)
#else
while (1)
{
- stop_soon_quietly = 1; /* Make wait_for_inferior be quiet */
+ /* Make wait_for_inferior be quiet */
+ stop_soon_quietly = STOP_QUIETLY;
wait_for_inferior ();
if (stop_signal != TARGET_SIGNAL_TRAP)
{
@@ -444,5 +445,5 @@ startup_inferior (int ntraps)
}
}
#endif /* STARTUP_INFERIOR */
- stop_soon_quietly = 0;
+ stop_soon_quietly = NO_STOP_QUIETLY;
}
Index: infcmd.c
===================================================================
RCS file: /cvs/uberbaum/gdb/infcmd.c,v
retrieving revision 1.72
diff -u -p -r1.72 infcmd.c
--- infcmd.c 1 Feb 2003 17:28:40 -0000 1.72
+++ infcmd.c 18 Feb 2003 20:24:38 -0000
@@ -1913,8 +1913,13 @@ attach_command (char *args, int from_tty
/* No traps are generated when attaching to inferior under Mach 3
or GNU hurd. */
#ifndef ATTACH_NO_WAIT
- stop_soon_quietly = 1;
+ /* Careful here. See comments in inferior.h. Basically some OSes
+ don't ignore SIGSTOPs on continue requests anymore. We need a
+ way for handle_inferior_event to reset the stop_signal variable
+ after an attach, and this is what STOP_QUIETLY_NO_SIGSTOP is for. */
+ stop_soon_quietly = STOP_QUIETLY_NO_SIGSTOP;
wait_for_inferior ();
+ stop_soon_quietly = NO_STOP_QUIETLY;
#endif
/*
Index: inferior.h
===================================================================
RCS file: /cvs/uberbaum/gdb/inferior.h,v
retrieving revision 1.42
diff -u -p -r1.42 inferior.h
--- inferior.h 21 Jan 2003 19:43:47 -0000 1.42
+++ inferior.h 18 Feb 2003 20:24:38 -0000
@@ -392,12 +392,37 @@ extern enum step_over_calls_kind step_ov
extern int step_multi;
-/* Nonzero means expecting a trap and caller will handle it themselves.
- It is used after attach, due to attaching to a process;
- when running in the shell before the child program has been exec'd;
- and when running some kinds of remote stuff (FIXME?). */
+/* Nonzero means expecting a trap and caller will handle it
+ themselves. It is used when running in the shell before the child
+ program has been exec'd; and when running some kinds of remote
+ stuff (FIXME?). */
-extern int stop_soon_quietly;
+/* It is also used after attach, due to attaching to a process. This
+ is a bit trickier. When doing an attach, the kernel stops the
+ debuggee with a SIGSTOP. On newer GNU/Linux kernels (>= 2.5.61)
+ the handling of SIGSTOP for a ptraced process has changed. Earlier
+ versions of the kernel would ignore these SIGSTOPs, while now
+ SIGSTOP is treated like any other signal, i.e. it is not muffled.
+
+ If the gdb user does a 'continue' after the 'attach', gdb passes
+ the global variable stop_signal (which stores the signal from the
+ attach, SIGSTOP) to the ptrace(PTRACE_CONT,...) call. This is
+ problematic, because the kernel doesn't ignore such SIGSTOP
+ now. I.e. it is reported back to gdb, which in turn presents it
+ back to the user.
+
+ To avoid the problem, we use STOP_QUIETLY_NO_SIGSTOP, which allows
+ gdb to clear the value of stop_signal after the attach, so that it
+ is not passed back down to the kernel. */
+
+enum stop_kind
+ {
+ NO_STOP_QUIETLY = 0,
+ STOP_QUIETLY,
+ STOP_QUIETLY_NO_SIGSTOP
+ };
+
+extern enum stop_kind stop_soon_quietly;
/* Nonzero if proceed is being used for a "finish" command or a similar
situation when stop_registers should be saved. */
Index: infrun.c
===================================================================
RCS file: /cvs/uberbaum/gdb/infrun.c,v
retrieving revision 1.96
diff -u -p -r1.96 infrun.c
--- infrun.c 31 Jan 2003 15:22:57 -0000 1.96
+++ infrun.c 18 Feb 2003 20:24:42 -0000
@@ -306,7 +306,7 @@ int stop_after_trap;
when running in the shell before the child program has been exec'd;
and when running some kinds of remote stuff (FIXME?). */
-int stop_soon_quietly;
+enum stop_kind stop_soon_quietly;
/* Nonzero if proceed is being used for a "finish" command or a similar
situation when stop_registers should be saved. */
@@ -679,7 +679,7 @@ clear_proceed_status (void)
step_frame_id = null_frame_id;
step_over_calls = STEP_OVER_UNDEBUGGABLE;
stop_after_trap = 0;
- stop_soon_quietly = 0;
+ stop_soon_quietly = NO_STOP_QUIETLY;
proceed_to_finish = 0;
breakpoint_proceeded = 1; /* We're about to proceed... */
@@ -822,7 +822,7 @@ start_remote (void)
{
init_thread_list ();
init_wait_for_inferior ();
- stop_soon_quietly = 1;
+ stop_soon_quietly = STOP_QUIETLY;
trap_expected = 0;
/* Always go on waiting for the target, regardless of the mode. */
@@ -1261,7 +1261,7 @@ handle_inferior_event (struct execution_
might be the shell which has just loaded some objects,
otherwise add the symbols for the newly loaded objects. */
#ifdef SOLIB_ADD
- if (!stop_soon_quietly)
+ if (stop_soon_quietly == NO_STOP_QUIETLY)
{
/* Remove breakpoints, SOLIB_ADD might adjust
breakpoint addresses via breakpoint_re_set. */
@@ -1760,7 +1760,9 @@ handle_inferior_event (struct execution_
if (stop_signal == TARGET_SIGNAL_TRAP
|| (breakpoints_inserted &&
(stop_signal == TARGET_SIGNAL_ILL
- || stop_signal == TARGET_SIGNAL_EMT)) || stop_soon_quietly)
+ || stop_signal == TARGET_SIGNAL_EMT))
+ || stop_soon_quietly == STOP_QUIETLY
+ || stop_soon_quietly == STOP_QUIETLY_NO_SIGSTOP)
{
if (stop_signal == TARGET_SIGNAL_TRAP && stop_after_trap)
{
@@ -1768,9 +1770,24 @@ handle_inferior_event (struct execution_
stop_stepping (ecs);
return;
}
- if (stop_soon_quietly)
+
+ /* This is originated from start_remote(), start_inferior() and
+ shared libraries hook functions. */
+ if (stop_soon_quietly == STOP_QUIETLY)
{
stop_stepping (ecs);
+ return;
+ }
+
+ /* This originates from attach_command(). We need to overwrite
+ the stop_signal here, because some kernels don't ignore a
+ SIGSTOP in a subsequent ptrace(PTRACE_SONT,SOGSTOP) call.
+ See more comments in inferior.h. */
+ if (stop_soon_quietly == STOP_QUIETLY_NO_SIGSTOP)
+ {
+ stop_stepping (ecs);
+ if (stop_signal == TARGET_SIGNAL_STOP)
+ stop_signal = TARGET_SIGNAL_0;
return;
}
Index: mips-tdep.c
===================================================================
RCS file: /cvs/uberbaum/gdb/mips-tdep.c,v
retrieving revision 1.161
diff -u -p -r1.161 mips-tdep.c
--- mips-tdep.c 28 Jan 2003 16:31:11 -0000 1.161
+++ mips-tdep.c 18 Feb 2003 20:24:49 -0000
@@ -1789,7 +1789,7 @@ heuristic_proc_start (CORE_ADDR pc)
stop_soon_quietly, but with this test, at least we
don't print out warnings for every child forked (eg, on
decstation). 22apr93 rich@cygnus.com. */
- if (!stop_soon_quietly)
+ if (stop_soon_quietly == NO_STOP_QUIETLY)
{
static int blurb_printed = 0;
Index: remote-vx.c
===================================================================
RCS file: /cvs/uberbaum/gdb/remote-vx.c,v
retrieving revision 1.23
diff -u -p -r1.23 remote-vx.c
--- remote-vx.c 18 Jan 2003 15:55:52 -0000 1.23
+++ remote-vx.c 18 Feb 2003 20:24:50 -0000
@@ -67,7 +67,7 @@
extern void vx_read_register ();
extern void vx_write_register ();
extern void symbol_file_command ();
-extern int stop_soon_quietly; /* for wait_for_inferior */
+extern enum stop_kind stop_soon_quietly; /* for wait_for_inferior */
static int net_step ();
static int net_ptrace_clnt_call (); /* Forward decl */
@@ -243,9 +243,9 @@ vx_create_inferior (char *exec_file, cha
/* Install inferior's terminal modes. */
target_terminal_inferior ();
- stop_soon_quietly = 1;
+ stop_soon_quietly = STOP_QUIETLY;
wait_for_inferior (); /* Get the task spawn event */
- stop_soon_quietly = 0;
+ stop_soon_quietly = NO_STOP_QUIETLY;
/* insert_step_breakpoint (); FIXME, do we need this? */
proceed (-1, TARGET_SIGNAL_DEFAULT, 0);
Index: solib-irix.c
===================================================================
RCS file: /cvs/uberbaum/gdb/solib-irix.c,v
retrieving revision 1.1
diff -u -p -r1.1 solib-irix.c
--- solib-irix.c 27 Jul 2002 01:05:07 -0000 1.1
+++ solib-irix.c 18 Feb 2003 20:24:51 -0000
@@ -436,7 +436,7 @@ irix_solib_create_inferior_hook (void)
out what we need to know about them. */
clear_proceed_status ();
- stop_soon_quietly = 1;
+ stop_soon_quietly = STOP_QUIETLY;
stop_signal = TARGET_SIGNAL_0;
do
{
@@ -462,7 +462,7 @@ irix_solib_create_inferior_hook (void)
Delaying the resetting of stop_soon_quietly until after symbol loading
suppresses the warning. */
solib_add ((char *) 0, 0, (struct target_ops *) 0, auto_solib_add);
- stop_soon_quietly = 0;
+ stop_soon_quietly = NO_STOP_QUIETLY;
re_enable_breakpoints_in_shlibs ();
}
Index: solib-osf.c
===================================================================
RCS file: /cvs/uberbaum/gdb/solib-osf.c,v
retrieving revision 1.4
diff -u -p -r1.4 solib-osf.c
--- solib-osf.c 2 Jul 2002 17:05:28 -0000 1.4
+++ solib-osf.c 18 Feb 2003 20:24:51 -0000
@@ -321,7 +321,7 @@ osf_solib_create_inferior_hook (void)
out what we need to know about them. */
clear_proceed_status ();
- stop_soon_quietly = 1;
+ stop_soon_quietly = STOP_QUIETLY;
stop_signal = TARGET_SIGNAL_0;
do
{
@@ -337,7 +337,7 @@ osf_solib_create_inferior_hook (void)
Delaying the resetting of stop_soon_quietly until after symbol loading
suppresses the warning. */
solib_add ((char *) 0, 0, (struct target_ops *) 0, auto_solib_add);
- stop_soon_quietly = 0;
+ stop_soon_quietly = NO_STOP_QUIETLY;
/* Enable breakpoints disabled (unnecessarily) by clear_solib(). */
re_enable_breakpoints_in_shlibs ();
Index: solib-sunos.c
===================================================================
RCS file: /cvs/uberbaum/gdb/solib-sunos.c,v
retrieving revision 1.7
diff -u -p -r1.7 solib-sunos.c
--- solib-sunos.c 3 Feb 2003 20:39:41 -0000 1.7
+++ solib-sunos.c 18 Feb 2003 20:24:52 -0000
@@ -829,7 +829,7 @@ sunos_solib_create_inferior_hook (void)
out what we need to know about them. */
clear_proceed_status ();
- stop_soon_quietly = 1;
+ stop_soon_quietly = STOP_QUIETLY;
stop_signal = TARGET_SIGNAL_0;
do
{
@@ -837,7 +837,7 @@ sunos_solib_create_inferior_hook (void)
wait_for_inferior ();
}
while (stop_signal != TARGET_SIGNAL_TRAP);
- stop_soon_quietly = 0;
+ stop_soon_quietly = NO_STOP_QUIETLY;
/* We are now either at the "mapping complete" breakpoint (or somewhere
else, a condition we aren't prepared to deal with anyway), so adjust
Index: solib-svr4.c
===================================================================
RCS file: /cvs/uberbaum/gdb/solib-svr4.c,v
retrieving revision 1.29
diff -u -p -r1.29 solib-svr4.c
--- solib-svr4.c 18 Jan 2003 15:55:52 -0000 1.29
+++ solib-svr4.c 18 Feb 2003 20:24:53 -0000
@@ -1290,7 +1290,7 @@ svr4_solib_create_inferior_hook (void)
out what we need to know about them. */
clear_proceed_status ();
- stop_soon_quietly = 1;
+ stop_soon_quietly = STOP_QUIETLY;
stop_signal = TARGET_SIGNAL_0;
do
{
@@ -1298,7 +1298,7 @@ svr4_solib_create_inferior_hook (void)
wait_for_inferior ();
}
while (stop_signal != TARGET_SIGNAL_TRAP);
- stop_soon_quietly = 0;
+ stop_soon_quietly = NO_STOP_QUIETLY;
#endif /* defined(_SCO_DS) */
}