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, 20 insertions, 1 deletions

diff --git a/gdb/symtab.h b/gdb/symtab.h
index 746b5e6..eb14f34 100644
--- a/gdb/symtab.h
+++ b/gdb/symtab.h
@@ -1725,12 +1725,31 @@ extern struct symbol *find_symbol_at_address (CORE_ADDR);
    This might suggest that *ADDRESS and *ENDADDR ought to be set to the
    limits of the entry pc range, but that will cause the 
    *ADDRESS <= PC < *ENDADDR condition to be violated; many of the
-   callers of find_pc_partial_function expect this condition to hold.  */
+   callers of find_pc_partial_function expect this condition to hold. 
+
+   Callers which require the start and/or end addresses for the range
+   containing the entry pc should instead call
+   find_function_entry_range_from_pc.  */
 
 extern int find_pc_partial_function (CORE_ADDR pc, const char **name,
 				     CORE_ADDR *address, CORE_ADDR *endaddr,
 				     const struct block **block = nullptr);
 
+/* Like find_pc_partial_function, above, but *ADDRESS and *ENDADDR are
+   set to start and end addresses of the range containing the entry pc.
+
+   Note that it is not necessarily the case that (for non-NULL ADDRESS
+   and ENDADDR arguments) the *ADDRESS <= PC < *ENDADDR condition will
+   hold.
+
+   See comment for find_pc_partial_function, above, for further
+   explanation.  */
+
+extern bool find_function_entry_range_from_pc (CORE_ADDR pc,
+					       const char **name,
+					       CORE_ADDR *address,
+					       CORE_ADDR *endaddr);
+
 /* Return the type of a function with its first instruction exactly at
    the PC address.  Return NULL otherwise.  */