[PATCH] Return unconditionally ptid.pid () in get_ptrace_pid() for NetBSD

[PATCH] Return unconditionally ptid.pid () in get_ptrace_pid() for NetBSD

[Kamil Rytarowski]

NetBSD tracks the PID and LWP pair separately and both values are
needed and meaningful.
---
 gdb/inf-ptrace.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/gdb/inf-ptrace.c b/gdb/inf-ptrace.c
index db17a76d946..6a6cb554ba7 100644
--- a/gdb/inf-ptrace.c
+++ b/gdb/inf-ptrace.c
@@ -321,10 +321,14 @@ get_ptrace_pid (ptid_t ptid)
 {
   pid_t pid;

+#if !defined(__NetBSD__)
   /* If we have an LWPID to work with, use it.  Otherwise, we're
-     dealing with a non-threaded program/target.  */
+     dealing with a non-threaded program/target.
+
+     NetBSD tracks the PID and LWP pair separately. */
   pid = ptid.lwp ();
   if (pid == 0)
+#endif
     pid = ptid.pid ();
   return pid;
 }
--
2.25.0

Re: [PATCH] Return unconditionally ptid.pid () in get_ptrace_pid() for NetBSD

[Simon Marchi]

On 2020-03-17 12:30 p.m., Kamil Rytarowski wrote:
> NetBSD tracks the PID and LWP pair separately and both values are
> needed and meaningful.
> ---
>  gdb/inf-ptrace.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/gdb/inf-ptrace.c b/gdb/inf-ptrace.c
> index db17a76d946..6a6cb554ba7 100644
> --- a/gdb/inf-ptrace.c
> +++ b/gdb/inf-ptrace.c
> @@ -321,10 +321,14 @@ get_ptrace_pid (ptid_t ptid)
>  {
>    pid_t pid;
> 
> +#if !defined(__NetBSD__)
>    /* If we have an LWPID to work with, use it.  Otherwise, we're
> -     dealing with a non-threaded program/target.  */
> +     dealing with a non-threaded program/target.
> +
> +     NetBSD tracks the PID and LWP pair separately. */
>    pid = ptid.lwp ();
>    if (pid == 0)
> +#endif
>      pid = ptid.pid ();
>    return pid;
>  }
> --
> 2.25.0
> 

I think you should just avoid using get_ptrace_pid on NetBSD altogether, since
it is meant for OSes that require passing a single thread identifier to ptrace
(whereas NetBSD requires the (pid, lwp) pair).

Even with this modification in get_ptrace_pid, you need to change all the ptrace
call sites to pass the lwp on top of it.

I would suggest to instead #ifdef out get_ptrace_pid entirely on NetBSD, to avoid
using it by mistake, and just replace all ptrace call sites possibly used on BSD
to be

  ptrace (request, ptid.pid (), addr, ptid.lwp ());

This matches what I suggested in:

  https://sourceware.org/pipermail/gdb-patches/2020-March/166735.html

Simon

Re: [PATCH] Return unconditionally ptid.pid () in get_ptrace_pid() for NetBSD

[Kamil Rytarowski]

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On 17.03.2020 17:39, Simon Marchi wrote:
> On 2020-03-17 12:30 p.m., Kamil Rytarowski wrote:
>> NetBSD tracks the PID and LWP pair separately and both values are
>> needed and meaningful.
>> ---
>>  gdb/inf-ptrace.c | 6 +++++-
>>  1 file changed, 5 insertions(+), 1 deletion(-)
>>
>> diff --git a/gdb/inf-ptrace.c b/gdb/inf-ptrace.c
>> index db17a76d946..6a6cb554ba7 100644
>> --- a/gdb/inf-ptrace.c
>> +++ b/gdb/inf-ptrace.c
>> @@ -321,10 +321,14 @@ get_ptrace_pid (ptid_t ptid)
>>  {
>>    pid_t pid;
>>
>> +#if !defined(__NetBSD__)
>>    /* If we have an LWPID to work with, use it.  Otherwise, we're
>> -     dealing with a non-threaded program/target.  */
>> +     dealing with a non-threaded program/target.
>> +
>> +     NetBSD tracks the PID and LWP pair separately. */
>>    pid = ptid.lwp ();
>>    if (pid == 0)
>> +#endif
>>      pid = ptid.pid ();
>>    return pid;
>>  }
>> --
>> 2.25.0
>>
> 
> I think you should just avoid using get_ptrace_pid on NetBSD altogether, since
> it is meant for OSes that require passing a single thread identifier to ptrace
> (whereas NetBSD requires the (pid, lwp) pair).
> 
> Even with this modification in get_ptrace_pid, you need to change all the ptrace
> call sites to pass the lwp on top of it.
> 
> I would suggest to instead #ifdef out get_ptrace_pid entirely on NetBSD, to avoid
> using it by mistake, and just replace all ptrace call sites possibly used on BSD
> to be
> 
>   ptrace (request, ptid.pid (), addr, ptid.lwp ());
> 
> This matches what I suggested in:
> 
>   https://sourceware.org/pipermail/gdb-patches/2020-March/166735.html
> 
> Simon
> 

Avoiding is possibly nice.. however in the current code it is much more
intrusive. We would need to patch now generic and OS/CPU specific code
(some of that is also shared with other OSs due to legacy reasons).

I think it is much cleaner to return ptid. pid() for NetBSD and reflect
the meaning of get_ptrace_pid().

If I follow your advice I end up with ifdefs like here:

diff --git a/gdb/inf-ptrace.c b/gdb/inf-ptrace.c
index b63a1bf88ef..a5d9c1d10ea 100644
--- a/gdb/inf-ptrace.c
+++ b/gdb/inf-ptrace.c
@@ -349,7 +349,11 @@ inf_ptrace_target::resume (ptid_t ptid, int step,
enum gdb_signal signal)
        single-threaded processes, so simply resume the inferior.  */
     pid = inferior_ptid.pid ();
   else
+#ifdef __NetBSD__
+    pid = ptid. pid();
+#else
     pid = get_ptrace_pid (ptid);
+#endif

   if (catch_syscall_enabled () > 0)
     request = PT_SYSCALL;
@@ -533,7 +537,11 @@ inf_ptrace_target::xfer_partial (enum target_object
object,
 				 const gdb_byte *writebuf,
 				 ULONGEST offset, ULONGEST len, ULONGEST *xfered_len)
 {
+#ifdef __NetBSD__
+  pid_t pid = inferior_ptid. pid();
+#else
   pid_t pid = get_ptrace_pid (inferior_ptid);
+#endif

   switch (object)
     {

Maintaining that will be certainly harder and it will be prone to
recurring regressions.

If we want to take the route of cleanups and refactoring I think it
would be better to rethink the pid,lwp separation in Linux; but that is
much beyond the scope of my patches.

Last but not least, get_ptrace_pid() would work now for NetBSD literally
as specified in the function name now... just extracting pid from ptid,
not calculating it from lwp/pid. It's now questionable whether a wrapper
function is still needed, but that would be optimized to .pid () in future.


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Re: [PATCH] Return unconditionally ptid.pid () in get_ptrace_pid() for NetBSD

[Simon Marchi]

On 2020-03-17 1:45 p.m., Kamil Rytarowski wrote:
> On 17.03.2020 17:39, Simon Marchi wrote:
>> On 2020-03-17 12:30 p.m., Kamil Rytarowski wrote:
>>> NetBSD tracks the PID and LWP pair separately and both values are
>>> needed and meaningful.
>>> ---
>>>  gdb/inf-ptrace.c | 6 +++++-
>>>  1 file changed, 5 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/gdb/inf-ptrace.c b/gdb/inf-ptrace.c
>>> index db17a76d946..6a6cb554ba7 100644
>>> --- a/gdb/inf-ptrace.c
>>> +++ b/gdb/inf-ptrace.c
>>> @@ -321,10 +321,14 @@ get_ptrace_pid (ptid_t ptid)
>>>  {
>>>    pid_t pid;
>>>
>>> +#if !defined(__NetBSD__)
>>>    /* If we have an LWPID to work with, use it.  Otherwise, we're
>>> -     dealing with a non-threaded program/target.  */
>>> +     dealing with a non-threaded program/target.
>>> +
>>> +     NetBSD tracks the PID and LWP pair separately. */
>>>    pid = ptid.lwp ();
>>>    if (pid == 0)
>>> +#endif
>>>      pid = ptid.pid ();
>>>    return pid;
>>>  }
>>> --
>>> 2.25.0
>>>
>>
>> I think you should just avoid using get_ptrace_pid on NetBSD altogether, since
>> it is meant for OSes that require passing a single thread identifier to ptrace
>> (whereas NetBSD requires the (pid, lwp) pair).
>>
>> Even with this modification in get_ptrace_pid, you need to change all the ptrace
>> call sites to pass the lwp on top of it.
>>
>> I would suggest to instead #ifdef out get_ptrace_pid entirely on NetBSD, to avoid
>> using it by mistake, and just replace all ptrace call sites possibly used on BSD
>> to be
>>
>>   ptrace (request, ptid.pid (), addr, ptid.lwp ());
>>
>> This matches what I suggested in:
>>
>>   https://sourceware.org/pipermail/gdb-patches/2020-March/166735.html
>>
>> Simon
>>
> 
> Avoiding is possibly nice.. however in the current code it is much more
> intrusive. We would need to patch now generic and OS/CPU specific code
> (some of that is also shared with other OSs due to legacy reasons).
> 
> I think it is much cleaner to return ptid. pid() for NetBSD and reflect
> the meaning of get_ptrace_pid().
> 
> If I follow your advice I end up with ifdefs like here:
> 
> diff --git a/gdb/inf-ptrace.c b/gdb/inf-ptrace.c
> index b63a1bf88ef..a5d9c1d10ea 100644
> --- a/gdb/inf-ptrace.c
> +++ b/gdb/inf-ptrace.c
> @@ -349,7 +349,11 @@ inf_ptrace_target::resume (ptid_t ptid, int step,
> enum gdb_signal signal)
>         single-threaded processes, so simply resume the inferior.  */
>      pid = inferior_ptid.pid ();
>    else
> +#ifdef __NetBSD__
> +    pid = ptid. pid();
> +#else
>      pid = get_ptrace_pid (ptid);
> +#endif
> 
>    if (catch_syscall_enabled () > 0)
>      request = PT_SYSCALL;
> @@ -533,7 +537,11 @@ inf_ptrace_target::xfer_partial (enum target_object
> object,
>  				 const gdb_byte *writebuf,
>  				 ULONGEST offset, ULONGEST len, ULONGEST *xfered_len)
>  {
> +#ifdef __NetBSD__
> +  pid_t pid = inferior_ptid. pid();
> +#else
>    pid_t pid = get_ptrace_pid (inferior_ptid);
> +#endif
> 
>    switch (object)
>      {

I was thinking more about using a "gdb_ptrace" function in this file, as
you have added in the other patch.  The only ifdef would be in that function.
get_ptrace_pid would only be used in the !__NetBSD__ branch of that function.

inf_ptrace_target::xfer_partial and inf_ptrace_target::resume would just call
gdb_ptrace, passing the right ptid.

> Maintaining that will be certainly harder and it will be prone to
> recurring regressions.
> 
> If we want to take the route of cleanups and refactoring I think it
> would be better to rethink the pid,lwp separation in Linux; but that is
> much beyond the scope of my patches.

I'm not sure what do mean by "rethink the pid,lwp separation in Linux".

> Last but not least, get_ptrace_pid() would work now for NetBSD literally
> as specified in the function name now... just extracting pid from ptid,
> not calculating it from lwp/pid. It's now questionable whether a wrapper
> function is still needed, but that would be optimized to .pid () in future.

Yeah, but since NetBSD doesn't need get_ptrace_pid, I'd like if we could avoid
making get_ptrace_pid more complex and if the ifdefs were concentrated around
the ptrace calls (ideally, in as few spots possible, thanks to the gdb_ptrace
functions).

Simon

Re: [PATCH] Return unconditionally ptid.pid () in get_ptrace_pid() for NetBSD

[Kamil Rytarowski]

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On 17.03.2020 20:00, Simon Marchi wrote:
> On 2020-03-17 1:45 p.m., Kamil Rytarowski wrote:
>> On 17.03.2020 17:39, Simon Marchi wrote:
>>> On 2020-03-17 12:30 p.m., Kamil Rytarowski wrote:
>>>> NetBSD tracks the PID and LWP pair separately and both values are
>>>> needed and meaningful.
>>>> ---
>>>>  gdb/inf-ptrace.c | 6 +++++-
>>>>  1 file changed, 5 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/gdb/inf-ptrace.c b/gdb/inf-ptrace.c
>>>> index db17a76d946..6a6cb554ba7 100644
>>>> --- a/gdb/inf-ptrace.c
>>>> +++ b/gdb/inf-ptrace.c
>>>> @@ -321,10 +321,14 @@ get_ptrace_pid (ptid_t ptid)
>>>>  {
>>>>    pid_t pid;
>>>>
>>>> +#if !defined(__NetBSD__)
>>>>    /* If we have an LWPID to work with, use it.  Otherwise, we're
>>>> -     dealing with a non-threaded program/target.  */
>>>> +     dealing with a non-threaded program/target.
>>>> +
>>>> +     NetBSD tracks the PID and LWP pair separately. */
>>>>    pid = ptid.lwp ();
>>>>    if (pid == 0)
>>>> +#endif
>>>>      pid = ptid.pid ();
>>>>    return pid;
>>>>  }
>>>> --
>>>> 2.25.0
>>>>
>>>
>>> I think you should just avoid using get_ptrace_pid on NetBSD altogether, since
>>> it is meant for OSes that require passing a single thread identifier to ptrace
>>> (whereas NetBSD requires the (pid, lwp) pair).
>>>
>>> Even with this modification in get_ptrace_pid, you need to change all the ptrace
>>> call sites to pass the lwp on top of it.
>>>
>>> I would suggest to instead #ifdef out get_ptrace_pid entirely on NetBSD, to avoid
>>> using it by mistake, and just replace all ptrace call sites possibly used on BSD
>>> to be
>>>
>>>   ptrace (request, ptid.pid (), addr, ptid.lwp ());
>>>
>>> This matches what I suggested in:
>>>
>>>   https://sourceware.org/pipermail/gdb-patches/2020-March/166735.html
>>>
>>> Simon
>>>
>>
>> Avoiding is possibly nice.. however in the current code it is much more
>> intrusive. We would need to patch now generic and OS/CPU specific code
>> (some of that is also shared with other OSs due to legacy reasons).
>>
>> I think it is much cleaner to return ptid. pid() for NetBSD and reflect
>> the meaning of get_ptrace_pid().
>>
>> If I follow your advice I end up with ifdefs like here:
>>
>> diff --git a/gdb/inf-ptrace.c b/gdb/inf-ptrace.c
>> index b63a1bf88ef..a5d9c1d10ea 100644
>> --- a/gdb/inf-ptrace.c
>> +++ b/gdb/inf-ptrace.c
>> @@ -349,7 +349,11 @@ inf_ptrace_target::resume (ptid_t ptid, int step,
>> enum gdb_signal signal)
>>         single-threaded processes, so simply resume the inferior.  */
>>      pid = inferior_ptid.pid ();
>>    else
>> +#ifdef __NetBSD__
>> +    pid = ptid. pid();
>> +#else
>>      pid = get_ptrace_pid (ptid);
>> +#endif
>>
>>    if (catch_syscall_enabled () > 0)
>>      request = PT_SYSCALL;
>> @@ -533,7 +537,11 @@ inf_ptrace_target::xfer_partial (enum target_object
>> object,
>>  				 const gdb_byte *writebuf,
>>  				 ULONGEST offset, ULONGEST len, ULONGEST *xfered_len)
>>  {
>> +#ifdef __NetBSD__
>> +  pid_t pid = inferior_ptid. pid();
>> +#else
>>    pid_t pid = get_ptrace_pid (inferior_ptid);
>> +#endif
>>
>>    switch (object)
>>      {
> 
> I was thinking more about using a "gdb_ptrace" function in this file, as
> you have added in the other patch.  The only ifdef would be in that function.
> get_ptrace_pid would only be used in the !__NetBSD__ branch of that function.
> 
> inf_ptrace_target::xfer_partial and inf_ptrace_target::resume would just call
> gdb_ptrace, passing the right ptid.
> 
>> Maintaining that will be certainly harder and it will be prone to
>> recurring regressions.
>>
>> If we want to take the route of cleanups and refactoring I think it
>> would be better to rethink the pid,lwp separation in Linux; but that is
>> much beyond the scope of my patches.
> 
> I'm not sure what do mean by "rethink the pid,lwp separation in Linux".
> 

Please disregard. Refactoring (and removal assumptions about specific
threading model) is out of scope of my patches.

>> Last but not least, get_ptrace_pid() would work now for NetBSD literally
>> as specified in the function name now... just extracting pid from ptid,
>> not calculating it from lwp/pid. It's now questionable whether a wrapper
>> function is still needed, but that would be optimized to .pid () in future.
> 
> Yeah, but since NetBSD doesn't need get_ptrace_pid, I'd like if we could avoid
> making get_ptrace_pid more complex and if the ifdefs were concentrated around
> the ptrace calls (ideally, in as few spots possible, thanks to the gdb_ptrace
> functions).
> 
> Simon
> 

I've submitted a patch disabling get_ptrace_pid() for NetBSD and
switching in 2 places to ptid. pid()me file.

Not all ptrace(2) calls accept PID+LWP on NetBSD as here are calls that
work for the whole process such as DETACH, ATTACH, PT_SET_EVENT_MASK etc.

It's easier for now to go for this approach in the proposed patch.


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