[binutils-gdb] Fix fork-related regressions on GNU/Linux

[Pedro Alves <palves at sourceware dot org>]

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=2fd9d7ca17539ce983862b25e0abc27cfb706189

commit 2fd9d7ca17539ce983862b25e0abc27cfb706189
Author: Pedro Alves <palves@redhat.com>
Date:   Thu Oct 5 18:33:22 2017 +0100

    Fix fork-related regressions on GNU/Linux
    
    Commit 5cd63fda035d ("Fix "Remote 'g' packet reply is too long"
    problems with multiple inferiors") caused a number of regressions on
    native GNU/Linux, all related to follow-fork support.  E.g.:
    
      src/gdb/target.c:3141: internal-error: gdbarch* default_thread_architecture(target_ops*, ptid_t): Assertion `inf != NULL' failed.
      A problem internal to GDB has been detected,
      further debugging may prove unreliable.
      Quit this debugging session? (y or n)
      Resyncing due to internal error.
      FAIL: gdb.base/catch-signal-fork.exp: got SIGHUP after fork (GDB internal error)
    
    This commit fixes it.
    
    gdb/ChangeLog:
    2017-10-05  Pedro Alves  <palves@redhat.com>
    
    	* linux-nat.c (linux_child_follow_fork): When following the parent
    	and detaching the child, consult the parent thread's architecture
    	instead of the child's.

Diff:
---
 gdb/ChangeLog   | 6 ++++++
 gdb/linux-nat.c | 5 ++++-
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index f70aa8a..59eb04a 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,9 @@
+2017-10-05  Pedro Alves  <palves@redhat.com>
+
+	* linux-nat.c (linux_child_follow_fork): When following the parent
+	and detaching the child, consult the parent thread's architecture
+	instead of the child's.
+
 2017-10-05  Ulrich Weigand  <uweigand@de.ibm.com>
 
 	* ax.h: Do not include "doublest.h".
diff --git a/gdb/linux-nat.c b/gdb/linux-nat.c
index 0f340ee..6080415 100644
--- a/gdb/linux-nat.c
+++ b/gdb/linux-nat.c
@@ -510,8 +510,11 @@ linux_child_follow_fork (struct target_ops *ops, int follow_child,
 	     To work around this, single step the child process
 	     once before detaching to clear the flags.  */
 
+	  /* Note that we consult the parent's architecture instead of
+	     the child's because there's no inferior for the child at
+	     this point.  */
 	  if (!gdbarch_software_single_step_p (target_thread_architecture
-					       (child_lp->ptid)))
+					       (parent_ptid)))
 	    {
 	      linux_disable_event_reporting (child_pid);
 	      if (ptrace (PTRACE_SINGLESTEP, child_pid, 0, 0) < 0)