[PATCH] [master + gdb-13] Fix Solaris regression (PR tdep/30252)

[Pedro Alves <pedro@palves.net>]

PR tdep/30252 reports that using GDB on Solaris fails an assertion in
target_resume:

 target.c:2648: internal-error: target_resume: Assertion `inferior_ptid != null_ptid' failed.
 A problem internal to GDB has been detected,
 further debugging may prove unreliable.
 Quit this debugging session? (y or n)

The backtrace, after running it through c++filt, looks like:

 ----- Backtrace -----
 0xa18914 gdb_internal_backtrace_1
	 /root/binutils-gdb/gdb/bt-utils.c:122
 0xa18914 gdb_internal_backtrace()
	 /root/binutils-gdb/gdb/bt-utils.c:168
 0xdec834 internal_vproblem
	 /root/binutils-gdb/gdb/utils.c:401
 0xdecad8 internal_verror(char const*, int, char const*, __va_list_tag*)
	 /root/binutils-gdb/gdb/utils.c:481
 0xf3638c internal_error_loc(char const*, int, char const*, ...)
	 /root/binutils-gdb/gdbsupport/errors.cc:58
 0xd70580 target_resume(ptid_t, int, gdb_signal)
	 /root/binutils-gdb/gdb/target.c:2648
 0xc59e85 procfs_target::wait(ptid_t, target_waitstatus*, enum_flags<target_wait_flag>)
	 /root/binutils-gdb/gdb/procfs.c:2187
 0xcf6da7 sol_thread_target::wait(ptid_t, target_waitstatus*, enum_flags<target_wait_flag>)
	 /root/binutils-gdb/gdb/sol-thread.c:442
 0xd73711 target_wait(ptid_t, target_waitstatus*, enum_flags<target_wait_flag>)
	 /root/binutils-gdb/gdb/target.c:2586
 ...

The problem is that the procfs backend, while inside target_wait,
called target_resume without switching to the leader thread of that
resumption.

The target_resume interface is:

 /* Resume execution (or prepare for execution) of the current thread
    (INFERIOR_PTID), while optionally letting other threads of the
    current process or all processes run free.
    ...

Thus calling target_resume with inferior_ptid == null_ptid is bogus.

target_wait (which leads to procfs_target::wait on Solaris) is called
with inferior_ptid == null_ptid on entry exactly to help catch such
bogus uses.

From the backtrace, it seems that the relevant line in question is
procfs.c:2187:

2186  /* How to keep going without returning to wfi: */
2187  target_continue_no_signal (ptid);
2188  goto wait_again;

target_continue_no_signal is a small wrapper around target_resume,
which would make sense.

The fix is to not call target_resume or go via the target stack at
all.  Instead, factor out a new proc_resume function out of
procfs_target::resume, and call that.  The new function does not rely
on inferior_ptid.

I've not been able to test it myself, but Petr confirmed it fixes the
assertion failure with his test case.

Tested-By: Petr Šumbera <petr.sumbera@oracle.com>
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=30252
Change-Id: I9657f9a96f2bc7fded72b8a771e592b6b91efea3
---
 gdb/procfs.c | 46 +++++++++++++++++++++++++---------------------
 1 file changed, 25 insertions(+), 21 deletions(-)

diff --git a/gdb/procfs.c b/gdb/procfs.c
index 741e62a2402..75f3a182754 100644
--- a/gdb/procfs.c
+++ b/gdb/procfs.c
@@ -589,6 +589,8 @@ static int proc_iterate_over_threads
   (procinfo *pi,
    int (*func) (procinfo *, procinfo *, void *),
    void *ptr);
+static void proc_resume (procinfo *pi, ptid_t scope_ptid,
+			 int step, enum gdb_signal signo);
 
 static void
 proc_warn (procinfo *pi, const char *func, int line)
@@ -2119,7 +2121,7 @@ procfs_target::wait (ptid_t ptid, struct target_waitstatus *status,
 		      gdb_printf (_("[%s exited]\n"),
 				  target_pid_to_str (retval).c_str ());
 		    delete_thread (find_thread_ptid (this, retval));
-		    target_continue_no_signal (ptid);
+		    proc_resume (pi, ptid, 0, GDB_SIGNAL_0);
 		    goto wait_again;
 		  }
 		else if (what == SYS_exit)
@@ -2183,8 +2185,7 @@ procfs_target::wait (ptid_t ptid, struct target_waitstatus *status,
 				      i, sysargs[i]);
 		      }
 
-		    /* How to keep going without returning to wfi: */
-		    target_continue_no_signal (ptid);
+		    proc_resume (pi, ptid, 0, GDB_SIGNAL_0);
 		    goto wait_again;
 		  }
 		break;
@@ -2217,7 +2218,7 @@ procfs_target::wait (ptid_t ptid, struct target_waitstatus *status,
 		    if (!in_thread_list (this, temp_ptid))
 		      add_thread (this, temp_ptid);
 
-		    target_continue_no_signal (ptid);
+		    proc_resume (pi, ptid, 0, GDB_SIGNAL_0);
 		    goto wait_again;
 		  }
 		else if (what == SYS_lwp_exit)
@@ -2249,7 +2250,7 @@ procfs_target::wait (ptid_t ptid, struct target_waitstatus *status,
 				      i, sysargs[i]);
 		      }
 
-		    target_continue_no_signal (ptid);
+		    proc_resume (pi, ptid, 0, GDB_SIGNAL_0);
 		    goto wait_again;
 		  }
 		break;
@@ -2428,20 +2429,16 @@ invalidate_cache (procinfo *parent, procinfo *pi, void *ptr)
   return 0;
 }
 
-/* Make the child process runnable.  Normally we will then call
-   procfs_wait and wait for it to stop again (unless gdb is async).
+/* Make child process PI runnable.
 
    If STEP is true, then arrange for the child to stop again after
-   executing a single instruction.  If SIGNO is zero, then cancel any
-   pending signal; if non-zero, then arrange for the indicated signal
-   to be delivered to the child when it runs.  If PID is -1, then
-   allow any child thread to run; if non-zero, then allow only the
-   indicated thread to run.  (not implemented yet).  */
+   executing a single instruction.  SCOPE_PTID, STEP and SIGNO are
+   like in the target_resume interface.  */
 
-void
-procfs_target::resume (ptid_t ptid, int step, enum gdb_signal signo)
+static void
+proc_resume (procinfo *pi, ptid_t scope_ptid, int step, enum gdb_signal signo)
 {
-  procinfo *pi, *thread;
+  procinfo *thread;
   int native_signo;
 
   /* FIXME: Check/reword.  */
@@ -2453,10 +2450,6 @@ procfs_target::resume (ptid_t ptid, int step, enum gdb_signal signo)
      So basically PR_STEP is the sole argument that must be passed
      to proc_run_process.  */
 
-  /* Find procinfo for main process.  */
-  pi = find_procinfo_or_die (inferior_ptid.pid (), 0);
-
-  /* First cut: ignore pid argument.  */
   errno = 0;
 
   /* Convert signal to host numbering.  */
@@ -2473,11 +2466,11 @@ procfs_target::resume (ptid_t ptid, int step, enum gdb_signal signo)
   /* Void the process procinfo's caches.  */
   invalidate_cache (NULL, pi, NULL);
 
-  if (ptid.pid () != -1)
+  if (scope_ptid.pid () != -1)
     {
       /* Resume a specific thread, presumably suppressing the
 	 others.  */
-      thread = find_procinfo (ptid.pid (), ptid.lwp ());
+      thread = find_procinfo (scope_ptid.pid (), scope_ptid.lwp ());
       if (thread != NULL)
 	{
 	  if (thread->tid != 0)
@@ -2502,6 +2495,17 @@ procfs_target::resume (ptid_t ptid, int step, enum gdb_signal signo)
     }
 }
 
+/* Implementation of target_ops::resume.  */
+
+void
+procfs_target::resume (ptid_t scope_ptid, int step, enum gdb_signal signo)
+{
+  /* Find procinfo for main process.  */
+  procinfo *pi = find_procinfo_or_die (inferior_ptid.pid (), 0);
+
+  proc_resume (pi, scope_ptid, step, signo);
+}
+
 /* Set up to trace signals in the child process.  */
 
 void

base-commit: 80251d4185048c6391b74abe96c754e8a536b35f
-- 
2.36.0