[PATCH] Enable multi process debugging for AIX

[Aditya Kamath1 <Aditya.Kamath1@ibm.com>]

[-- Attachment #1: Type: text/plain, Size: 2662 bytes --]

Hi,


The attached proposed patch adds multi process debugging feature in AIX.”

Till now AIX supported debugging only one inferior at a time, now we can be able to debug multi process.

Users can use set follow fork mode in child or parent and set detach on fork on or off to enable/disable simultaneous debugging of parent/child.


An example program is written below as follows with the gdb output:

#include <stdio.h>

#include <sys/types.h>

#include <unistd.h>



void hello_from_child(){

  printf("Hello from child \n");

}



void hello_from_parent(){

  printf("Hello from Parent \n");

}



int main(){

  pid_t childpid;

  printf("I should not be printed after fork as I am executed \n");

  childpid = fork();

  if (childpid == 0)

   hello_from_child();

  else

    hello_from_parent();



  return 0;

}



GDB Output:-



(gdb) b hello_from_child

Breakpoint 1 at 0x10000584: file test_fork.c, line 6.

(gdb) set follow-fork-mode child

(gdb) set detach-on-fork off

(gdb) r

Starting program: /home/test_fork

I should not be printed after fork as I am executed

[Attaching after process 23331156 fork to child process 23134700]

[New inferior 2 (process 23134700)]

[Switching to process 23134700]



Thread 2.1 hit Breakpoint 1, hello_from_child ()

    at test_fork.c:6

6         printf("Hello from child \n");

(gdb) c

Continuing.

Hello from child

[Inferior 2 (process 23134700) exited normally]

(gdb)





The following are the results after running the "gdb.base" test suite:-



With patch



# of expected passes            26584
# of unexpected failures        3968
# of unexpected successes       1
# of expected failures          17
# of known failures             26
# of unresolved testcases       109
# of untested testcases         79
# of unsupported tests          62
# of paths in test names        1
# of duplicate test names       2



Without patch



# of expected passes 26244
# of unexpected failures 4230
# of unexpected successes 1
# of expected failures 17
# of known failures 26
# of unresolved testcases 110
# of untested testcases 79
# of unsupported tests 62
# of paths in test names 1
# of duplicate test names 4




Please find attached the patch [See file: 0001-Enable-multi-process-debugging-for-AIX.patch]


I have left comments in my patch to make it easy to understand and justify [code lines] the same. Let me know what you think.


Kindly give us feedback at the earliest.

Have a nice day ahead.


Thanks and regards,

Aditya.

Bye.


[-- Attachment #2: 0001-Enable-multi-process-debugging-for-AIX.patch --]
[-- Type: application/octet-stream, Size: 4303 bytes --]

From 1eab0bb05b1db09dfb98d31cc630722b40c081c4 Mon Sep 17 00:00:00 2001
From: Aditya Vidyadhar Kamath <Aditya.Kamath1@ibm.com>
Date: Tue, 19 Jul 2022 10:39:00 -0500
Subject: [PATCH] Enable multi process debugging for AIX

The attached proposed patch adds multi process debugging feature in AIX.

Till now AIX supported debugging only one inferior at a time,

now we can be able to debug multi process.

Users can use set follow fork mode in child or parent and

set detach on fork on or off to enable/disable simultaneous debugging of parent/child.
---
 gdb/aix-thread.c     |  4 ++++
 gdb/rs6000-aix-nat.c | 48 +++++++++++++++++++++++++++++++++++++++++---
 2 files changed, 49 insertions(+), 3 deletions(-)

diff --git a/gdb/aix-thread.c b/gdb/aix-thread.c
index d47f5132592..f66b5904ae8 100644
--- a/gdb/aix-thread.c
+++ b/gdb/aix-thread.c
@@ -1088,6 +1088,10 @@ aix_thread_target::wait (ptid_t ptid, struct target_waitstatus *status,
      pid-only ptids.  */
   gdb_assert (ptid.is_pid ());
 
+  /* In pd_activate to get PTHB_SUCCESS in pthread debug session init
+     we need inferior_ptid set to update multiple threads. */
+  inferior_ptid = ptid;
+
   /* Check whether libpthdebug might be ready to be initialized.  */
   if (!pd_active && status->kind () == TARGET_WAITKIND_STOPPED
       && status->sig () == GDB_SIGNAL_TRAP)
diff --git a/gdb/rs6000-aix-nat.c b/gdb/rs6000-aix-nat.c
index f604f7d503e..55844ca6dab 100644
--- a/gdb/rs6000-aix-nat.c
+++ b/gdb/rs6000-aix-nat.c
@@ -91,10 +91,16 @@ class rs6000_nat_target final : public inf_ptrace_target
 
   ptid_t wait (ptid_t, struct target_waitstatus *, target_wait_flags) override;
 
+  /* Fork detection related functions, For adding multi process debugging
+     support. */ 
+  void follow_fork (inferior *, ptid_t, target_waitkind, bool, bool) override;
+
+  void mourn_inferior () override;
+
 protected:
 
-  void post_startup_inferior (ptid_t ptid) override
-  { /* Nothing.  */ }
+  void post_startup_inferior (ptid_t ptid) override;
+  //{ /* Nothing.  */ }
 
 private:
   enum target_xfer_status
@@ -246,6 +252,22 @@ fetch_register (struct regcache *regcache, int regno)
     }
 }
 
+void rs6000_nat_target::post_startup_inferior(ptid_t ptid){
+  rs6000_ptrace64(PT_MULTI,ptid.pid(),NULL,1,NULL);
+}
+
+void
+rs6000_nat_target::follow_fork (inferior *child_inf, ptid_t child_ptid,
+                          target_waitkind fork_kind, bool follow_child,
+                                                      bool detach_fork)
+{
+  inf_ptrace_target::follow_fork(child_inf, child_ptid, fork_kind,
+                                        follow_child, detach_fork);
+}
+
+void rs6000_nat_target::mourn_inferior(){
+  inf_ptrace_target::mourn_inferior();
+}
 /* Store register REGNO back into the inferior.  */
 
 static void
@@ -539,8 +561,28 @@ rs6000_nat_target::wait (ptid_t ptid, struct target_waitstatus *ourstatus,
   if (status == 0x57c)
     ourstatus->set_loaded ();
   /* signal 0.  I have no idea why wait(2) returns with this status word.  */
-  else if (status == 0x7f)
+  /* 0x17f and 0x137f in hexadecimal are status returned if 
+     if we follow parent,
+     a switch is made to a child post parent execution
+     and child continues its execution [user switches to child and 
+     presses continue]. */
+  else if (status == 0x7f  || status == 0x17f || status == 0x137f)
     ourstatus->set_spurious ();
+  /* When a process completes execution and any fork process exits status. */
+  else if (WIFEXITED(status))
+    ourstatus->set_exited(0);
+  /* 57e is the status number in AIX for fork event.
+     If a breakpoint is attached to a parent or child then on fork,
+     or after fork, once a breakpoint hits and the next or continue is 
+     pressed, post breakpoint status is 1406 but we need not set status 
+     to set_forked(), hence the condition find_inferior_pid() to set 
+     fork status only if a child is born. */
+  else if (status == 0x57e && find_inferior_pid(this,pid)== nullptr)
+  {
+    ourstatus->set_forked (ptid_t(pid));
+    /* On a fork event return parent process ID to target wait */
+    return ptid_t(current_inferior()->pid);
+  }
   /* A normal waitstatus.  Let the usual macros deal with it.  */
   else
     *ourstatus = host_status_to_waitstatus (status);
-- 
2.31.1