Re: [PATCH] stepi/nexti: skip signal handler if "handle nostop" signal arrives

Pedro Alves
2014-10-14T18:49:47Z

On 10/14/2014 07:27 PM, Eli Zaretskii wrote:
>> From: Pedro Alves <palves@redhat.com>
>> Date: Tue, 14 Oct 2014 18:48:30 +0100
>>
>> --- a/gdb/doc/gdb.texinfo
>> +++ b/gdb/doc/gdb.texinfo
>> @@ -5526,6 +5526,11 @@ Their full names are:
>> @value{GDBN} should not stop your program when this signal happens. It may
>> still print a message telling you that the signal has come in.
>>
>> +If this signal arrives while a stepping command (e.g., @code{step}) is
>> +in progress, the signal's handler is skipped (though still executed if
>> +@code{pass} is in effect; see below). @value{GDBN} will still stop
>> +your program if the handler hits a breakpoint.
>
> This description is confusing. For starters, it only mentions some of
> the possible setting of signal handling, and keeps silence about the
> rest. Either we should describe what happens with all of them, one by
> one, or (better) says something that will explain how we handle them
> all, at once.

This paragraph is added to the "nostop" entry of the table. It directly
relates to the entry in question:

Specifically, it's a preemptive response to the question I'd have if
I read the paragraph just above, which talks about the signal but
leaves the question of the signal handler open:

@table @code
@item nostop
@value{GDBN} should not stop your program when this signal happens. It may
still print a message telling you that the signal has come in.

If this signal arrives while a stepping command (e.g., @code{step}) is
in progress, the signal's handler is skipped (though still executed if
@code{pass} is in effect; see below). @value{GDBN} will still stop
your program if the handler hits a breakpoint.

I could extend the "stop" item:

@item stop
@value{GDBN} should stop your program when this signal happens. This implies
the @code{print} keyword as well.

Like:

+ The signal is not visible to the program until you continue.

WDYT?

This is also said further below, after the table (and is what the
"see below" referred to):

When a signal stops your program, the signal is not visible to the
program until you
continue. Your program sees the signal then, if @code{pass} is in
effect for the signal in question @emph{at that time}. In other words,
after @value{GDBN} reports a signal, you can use the @code{handle}
command with @code{pass} or @code{nopass} to control whether your
program sees that signal when you continue.

+If a stepping command is issued after the program stops for a signal,
+and @code{pass} is in effect for that signal, @value{GDBN} steps into
+the signal's handler (if the target supports it).

The '+' lines are what I'm adding.
>
> Also, I believe the description of stepping should mention this
> aspect, with a cross-reference to here.

OK.

>
>> +If a stepping command is issued after the program stops for a signal,
>> +and @code{pass} is in effect for that signal, @value{GDBN} steps into
>> +the signal's handler (if the target supports it).
>
> Again, this left me wondering. E.g., if the program stops for a
> signal, then we are already in the signal handler, no?

No, we intercept the signal before the program sees it. See above.

> So the fact
> that stepping commands continue there is a no-brainer, right? Or a I
> again confused?

The latter. :-)

Thanks,
Pedro Alves