Add comments on step_after_step_resume_breakpoint

[Yao Qi <yao@codesourcery.com>]

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When I am reading struct thread_info, I find the comment on 
step_after_step_resume_breakpoint is not helpful to me to understand it, 
until I read the original patch here 
http://cygwin.com/ml/gdb-patches/2004-08/msg00743.html

The explanation of the patch was very clear, but it is missing in the 
comment of code.  This patch is to copy some of words in original patch 
post to the comment on field `step_after_step_resume_breakpoint', in 
order to make comment self-explained.

OK to apply?

-- 
Yao (齐尧)

[-- Attachment #2: 0002-comment-on-step_after_step_resume_breakpoint.patch --]
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	gdb/
	gdbthread.h (struct thread_info): Comment on field
	`step_after_step_resume_breakpoint'.

---
 gdb/gdbthread.h |    9 ++++++++-
 1 files changed, 8 insertions(+), 1 deletions(-)

diff --git a/gdb/gdbthread.h b/gdb/gdbthread.h
index 0b19a8d..6baeb92 100644
--- a/gdb/gdbthread.h
+++ b/gdb/gdbthread.h
@@ -176,7 +176,14 @@ struct thread_info
   int stepping_over_breakpoint;
 
   /* Set to TRUE if we should finish single-stepping over a breakpoint
-     after hitting the current step-resume breakpoint.  */
+     after hitting the current step-resume breakpoint.  The context here
+     is that GDB is to do `next' or `step' while signal arrives.
+     When stepping over a breakpoint and signal arrives, GDB will attempt
+     to skip signal handler, so it inserts a step_resume_breakpoint at the
+     signal return address, and resume inferior.
+     step_after_step_resume_breakpoint is set to TRUE at this moment in
+     order to keep GDB in mind that there is still a breakpoint to step over
+     when GDB gets back SIGTRAP from step_resume_breakpoint.  */
   int step_after_step_resume_breakpoint;
 
   /* This is set TRUE when a catchpoint of a shared library event
-- 
1.7.0.4