* infrun.c (resume): Clarify logic that

	decides if a single thread must be resumed. Add
	comments.

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index d9b296d70a97baf4c4f0cd430fd21f143e875a76..4b21d6e361477ac8424354fd5c0404aa7868f707 100644 (file)
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,9 @@
+2007-11-20  Vladimir Prus  <vladimir@codesourcery.com>
+
+       * infrun.c (resume): Clarify logic that
+       decides if a single thread must be resumed. Add
+       comments.
+
 2007-11-20  Vladimir Prus  <vladimir@codesourcery.com>
 
        * breakpoint.c (disable_breakpoints_in_unloaded_shlib):

diff --git a/gdb/infrun.c b/gdb/infrun.c
index cf7aa02abe1d7e4ce852acd7bfa6f2339cfd8ed2..85d889a5a29f043a2ca653faa8614745a46abeea 100644 (file)
--- a/gdb/infrun.c
+++ b/gdb/infrun.c
@@ -583,15 +583,41 @@ a command like `return' or `jump' to continue execution."));
 
       resume_ptid = RESUME_ALL;        /* Default */
 
-      if ((step || singlestep_breakpoints_inserted_p)
-         && (stepping_past_singlestep_breakpoint
-             || (!breakpoints_inserted && breakpoint_here_p (read_pc ()))))
+      /* If STEP is set, it's a request to use hardware stepping
+        facilities.  But in that case, we should never
+        use singlestep breakpoint.  */
+      gdb_assert (!(singlestep_breakpoints_inserted_p && step));
+
+      if (singlestep_breakpoints_inserted_p
+         && stepping_past_singlestep_breakpoint)
        {
-         /* Stepping past a breakpoint without inserting breakpoints.
-            Make sure only the current thread gets to step, so that
-            other threads don't sneak past breakpoints while they are
-            not inserted. */
+         /* The situation here is as follows.  In thread T1 we wanted to
+            single-step.  Lacking hardware single-stepping we've
+            set breakpoint at the PC of the next instruction -- call it
+            P.  After resuming, we've hit that breakpoint in thread T2.
+            Now we've removed original breakpoint, inserted breakpoint
+            at P+1, and try to step to advance T2 past breakpoint.
+            We need to step only T2, as if T1 is allowed to freely run,
+            it can run past P, and if other threads are allowed to run,
+            they can hit breakpoint at P+1, and nested hits of single-step
+            breakpoints is not something we'd want -- that's complicated
+            to support, and has no value.  */
+         resume_ptid = inferior_ptid;
+       }
 
+      if (step && breakpoint_here_p (read_pc ())
+         && !breakpoint_inserted_here_p (read_pc ()))
+       {
+         /* We're stepping, have breakpoint at PC, and it's 
+            not inserted.  Most likely, proceed has noticed that
+            we have breakpoint and tries to single-step over it,
+            so that it's not hit.  In which case, we need to
+            single-step only this thread, and keep others stopped,
+            as they can miss this breakpoint if allowed to run.  
+
+            The current code either has all breakpoints inserted, 
+            or all removed, so if we let other threads run,
+            we can actually miss any breakpoint, not the one at PC.  */
          resume_ptid = inferior_ptid;
        }