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

[Kamil Rytarowski <n54@gmx.com>]

[-- Attachment #1.1: Type: text/plain, Size: 3470 bytes --]

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.


[-- Attachment #2: OpenPGP digital signature --]
[-- Type: application/pgp-signature, Size: 833 bytes --]