[PATCH 1/3] btrace: work directly on begin and end pointers

[Markus Metzger <markus.t.metzger@intel.com>]

In ftrace_add_pt, we store copies of *PBEGIN and *PEND in local variables BEGIN
and END respectively.  The intent was to help the compiler figure out that BEGIN
and END are not changed over external function calls.

This is still true for most calls, yet if we want to allow changing *PBEGIN and
*PEND inside a function, we'd have to reload BEGIN and END after that call.
Stop using local copies to avoid that complication.

2017-04-28  Markus Metzger  <markus.t.metzger@intel.com>

gdb/
	* btrace.c (ftrace_add_pt): Rename arguments PBEGIN and PEND into
	BEGIN and END.  Use them directly.


---
 gdb/btrace.c | 53 +++++++++++++++++++++++------------------------------
 1 file changed, 23 insertions(+), 30 deletions(-)

diff --git a/gdb/btrace.c b/gdb/btrace.c
index 238df0a..6780e22 100644
--- a/gdb/btrace.c
+++ b/gdb/btrace.c
@@ -1137,16 +1137,13 @@ pt_btrace_insn (const struct pt_insn &insn)
 
 static void
 ftrace_add_pt (struct pt_insn_decoder *decoder,
-	       struct btrace_function **pbegin,
-	       struct btrace_function **pend, int *plevel,
+	       struct btrace_function **begin,
+	       struct btrace_function **end, int *plevel,
 	       VEC (bfun_s) **gaps)
 {
-  struct btrace_function *begin, *end, *upd;
   uint64_t offset;
   int errcode;
 
-  begin = *pbegin;
-  end = *pend;
   for (;;)
     {
       struct pt_insn insn;
@@ -1167,7 +1164,7 @@ ftrace_add_pt (struct pt_insn_decoder *decoder,
 	    break;
 
 	  /* Look for gaps in the trace - unless we're at the beginning.  */
-	  if (begin != NULL)
+	  if (*begin != NULL)
 	    {
 	      /* Tracing is disabled and re-enabled each time we enter the
 		 kernel.  Most times, we continue from the same instruction we
@@ -1176,65 +1173,61 @@ ftrace_add_pt (struct pt_insn_decoder *decoder,
 		 from some other instruction.  Indicate this as a trace gap.  */
 	      if (insn.enabled)
 		{
-		  *pend = end = ftrace_new_gap (end, BDE_PT_DISABLED);
+		  *end = ftrace_new_gap (*end, BDE_PT_DISABLED);
 
-		  VEC_safe_push (bfun_s, *gaps, end);
+		  VEC_safe_push (bfun_s, *gaps, *end);
 
 		  pt_insn_get_offset (decoder, &offset);
 
 		  warning (_("Non-contiguous trace at instruction %u (offset "
 			     "= 0x%" PRIx64 ", pc = 0x%" PRIx64 ")."),
-			   end->insn_offset - 1, offset, insn.ip);
+			   (*end)->insn_offset - 1, offset, insn.ip);
 		}
 	    }
 
 	  /* Indicate trace overflows.  */
 	  if (insn.resynced)
 	    {
-	      *pend = end = ftrace_new_gap (end, BDE_PT_OVERFLOW);
-	      if (begin == NULL)
-		*pbegin = begin = end;
+	      *end = ftrace_new_gap (*end, BDE_PT_OVERFLOW);
+	      if (*begin == NULL)
+		*begin = *end;
 
-	      VEC_safe_push (bfun_s, *gaps, end);
+	      VEC_safe_push (bfun_s, *gaps, *end);
 
 	      pt_insn_get_offset (decoder, &offset);
 
 	      warning (_("Overflow at instruction %u (offset = 0x%" PRIx64
-			 ", pc = 0x%" PRIx64 ")."), end->insn_offset - 1,
+			 ", pc = 0x%" PRIx64 ")."), (*end)->insn_offset - 1,
 		       offset, insn.ip);
 	    }
 
-	  upd = ftrace_update_function (end, insn.ip);
-	  if (upd != end)
-	    {
-	      *pend = end = upd;
-
-	      if (begin == NULL)
-		*pbegin = begin = upd;
-	    }
+	  *end = ftrace_update_function (*end, insn.ip);
+	  if (*begin == NULL)
+	    *begin = *end;
 
 	  /* Maintain the function level offset.  */
-	  *plevel = std::min (*plevel, end->level);
+	  *plevel = std::min (*plevel, (*end)->level);
 
 	  btrace_insn btinsn = pt_btrace_insn (insn);
-	  ftrace_update_insns (end, &btinsn);
+	  ftrace_update_insns (*end, &btinsn);
 	}
 
       if (errcode == -pte_eos)
 	break;
 
       /* Indicate the gap in the trace.  */
-      *pend = end = ftrace_new_gap (end, errcode);
-      if (begin == NULL)
-	*pbegin = begin = end;
+      *end = ftrace_new_gap (*end, errcode);
+      if (*begin == NULL)
+	*begin = *end;
 
-      VEC_safe_push (bfun_s, *gaps, end);
+      VEC_safe_push (bfun_s, *gaps, *end);
 
       pt_insn_get_offset (decoder, &offset);
 
       warning (_("Decode error (%d) at instruction %u (offset = 0x%" PRIx64
-		 ", pc = 0x%" PRIx64 "): %s."), errcode, end->insn_offset - 1,
-	       offset, insn.ip, pt_errstr (pt_errcode (errcode)));
+		 ", pc = 0x%" PRIx64 "): %s."), errcode,
+	       (*end)->insn_offset - 1, offset, insn.ip,
+	       pt_errstr (pt_errcode (errcode)));
     }
 }
 
-- 
1.8.3.1