[binutils-gdb] Conditionally restore displaced stepping state after fork.

[John Baldwin]

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=aeeb758df5a61a323de0095c28b3de1ee7b00db3

commit aeeb758df5a61a323de0095c28b3de1ee7b00db3
Author: John Baldwin <jhb@FreeBSD.org>
Date:   Tue Jun 1 14:22:20 2021 -0700

    Conditionally restore displaced stepping state after fork.
    
    There is no default method for
    gdbarch_displaced_step_restore_all_in_ptid, so calling it
    unconditionally for fork events triggered an assertion failure on
    platforms that do not support displaced stepping.  To fix, only invoke
    the method if the gdbarch supports displaced stepping.
    
    Note that not all gdbarches support both displaced stepping and fork
    events, so gdbarch validation does not require
    gdbarch_displaced_step_restore_all_in_ptid for any gdbarch supporting
    displaced stepping.  However, the internal assertion in
    gdbarch_displaced_step_restore_all_in_ptid should catch any gdbarches
    which do support both but fail to provide this method.
    
    gdb/ChangeLog:
    
            * infrun.c (handle_inferior_event): Only call
            gdbarch_displaced_step_restore_all_in_ptid if
            gdbarch_supports_displaced_stepping is true.

Diff:
---
 gdb/ChangeLog |  6 ++++++
 gdb/infrun.c  | 16 ++++++++++++----
 2 files changed, 18 insertions(+), 4 deletions(-)

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 1ca03b4e17a..6e5e88f9231 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,9 @@
+2021-06-01  John Baldwin  <jhb@FreeBSD.org>
+
+	* infrun.c (handle_inferior_event): Only call
+	gdbarch_displaced_step_restore_all_in_ptid if
+	gdbarch_supports_displaced_stepping is true.
+
 2021-06-01  Tom Tromey  <tromey@adacore.com>
 
 	* Makefile.in (all-data-directory): Remove.
diff --git a/gdb/infrun.c b/gdb/infrun.c
index e9624d2a9b6..488bcc1e10b 100644
--- a/gdb/infrun.c
+++ b/gdb/infrun.c
@@ -5493,10 +5493,18 @@ handle_inferior_event (struct execution_control_state *ecs)
 	struct gdbarch *gdbarch = regcache->arch ();
 	inferior *parent_inf = find_inferior_ptid (ecs->target, ecs->ptid);
 
-	/* If this is a fork (child gets its own address space copy) and some
-	   displaced step buffers were in use at the time of the fork, restore
-	   the displaced step buffer bytes in the child process.  */
-	if (ecs->ws.kind == TARGET_WAITKIND_FORKED)
+	/* If this is a fork (child gets its own address space copy)
+	   and some displaced step buffers were in use at the time of
+	   the fork, restore the displaced step buffer bytes in the
+	   child process.
+
+	   Architectures which support displaced stepping and fork
+	   events must supply an implementation of
+	   gdbarch_displaced_step_restore_all_in_ptid.  This is not
+	   enforced during gdbarch validation to support architectures
+	   which support displaced stepping but not forks.  */
+	if (ecs->ws.kind == TARGET_WAITKIND_FORKED
+	    && gdbarch_supports_displaced_stepping (gdbarch))
 	  gdbarch_displaced_step_restore_all_in_ptid
 	    (gdbarch, parent_inf, ecs->ws.value.related_pid);