Introduce find_function_entry_range_from_pc and use it in infrun.c

An earlier version of this patch used the returned block in conjunction
with BLOCK_ENTRY_PC to set stop_func_start in fill_in_stop_func() in
infrun.c.  While I think this was the correct thing to do, changes
to find_inferior_partial_function could potentially end up with
stop_func_end < stop_func_start, which is definitely wrong.  For
this case, we want to set both stop_func_start and stop_func_end
to the start and end of the range containing the function's entry
pc.

I think that this functionality will be useful in many other places
too - it probably ought to be used in all of the various prologue
analyzers in GDB.

The change to infrun.c was simple: the call to
find_pc_partial_function was replaced with a call to
find_function_entry_range_from_pc.  The difference between these two
functions is that find_pc_partial_entry_function will (potentially)
return the start and end address corresponding to the range in which
PC is found, but find_function_entry_range_from_pc will (again,
potentially) return the start and end address of the range containing
the entry pc.  find_pc_partial_function has the property that
*ADDRESS <= PC < *ENDADDR.  This condition does not necessarily hold
for the outputs of find_function_entry_range_from_pc.

It should be noted that for functions which contain only a single
range, the outputs of find_pc_partial_function and
find_function_entry_range_from_pc are identical.

I think it might happen that find_function_entry_range_from_pc will come
to be used in place of many of the calls to find_pc_partial_function
within GDB.  Care must be taken in making this change, however, since
some of this code depends on the *ADDRESS <= PC < *ENDADDR property.

Finally, a note regarding the name: I had initially chosen a different
name with a find_pc_partial_ prefix, but Simon suggested the current
name citing the goal of eventually making naming consistent using
the form find_X_from_Y.  In this case X is "function_entry_range" and
Y is "pc".  Both the name and rationale made sense to me, so that's
how it came to be.

gdb/ChangeLog:

	* infrun.c (fill_in_stop_func): Use find_function_entry_range_from_pc
	in place of find_pc_partial_function.
	* blockframe.c (find_function_entry_range_from_pc): New function.
	* symtab.h (find_function_entry_range_from_pc): Declare and document.

1 files changed, 37 insertions, 0 deletions

diff --git a/gdb/blockframe.c b/gdb/blockframe.c
index 6ea0965..f6dd861 100644
--- a/gdb/blockframe.c
+++ b/gdb/blockframe.c
@@ -377,6 +377,43 @@ find_pc_partial_function (CORE_ADDR pc, const char **name, CORE_ADDR *address,
 
 /* See symtab.h.  */
 
+bool
+find_function_entry_range_from_pc (CORE_ADDR pc, const char **name,
+				   CORE_ADDR *address, CORE_ADDR *endaddr)
+{
+  const struct block *block;
+  bool status = find_pc_partial_function (pc, name, address, endaddr, &block);
+
+  if (status && block != nullptr && !BLOCK_CONTIGUOUS_P (block))
+    {
+      CORE_ADDR entry_pc = BLOCK_ENTRY_PC (block);
+
+      for (int i = 0; i < BLOCK_NRANGES (block); i++)
+        {
+	  if (BLOCK_RANGE_START (block, i) <= entry_pc
+	      && entry_pc < BLOCK_RANGE_END (block, i))
+	    {
+	      if (address != nullptr)
+	        *address = BLOCK_RANGE_START (block, i);
+
+	      if (endaddr != nullptr)
+	        *endaddr = BLOCK_RANGE_END (block, i);
+
+	      return status;
+	    }
+	}
+
+      /* It's an internal error if we exit the above loop without finding
+         the range.  */
+      internal_error (__FILE__, __LINE__,
+                      _("Entry block not found in find_function_entry_range_from_pc"));
+    }
+
+  return status;
+}
+
+/* See symtab.h.  */
+
 struct type *
 find_function_type (CORE_ADDR pc)
 {