Add new overload of gdbarch_return_value

The gdbarch "return_value" can't correctly handle variably-sized
types.  The problem here is that the TYPE_LENGTH of such a type is 0,
until the type is resolved, which requires reading memory.  However,
gdbarch_return_value only accepts a buffer as an out parameter.

Fixing this requires letting the implementation of the gdbarch method
resolve the type and return a value -- that is, both the contents and
the new type.

After an attempt at this, I realized I wouldn't be able to correctly
update all implementations (there are ~80) of this method.  So,
instead, this patch adds a new method that falls back to the current
method, and it updates gdb to only call the new method.  This way it's
possible to incrementally convert the architectures that I am able to
test.

1 files changed, 19 insertions, 2 deletions

diff --git a/gdb/gdbarch-gen.h b/gdb/gdbarch-gen.h
index c2299dc..128efa1 100644
--- a/gdb/gdbarch-gen.h
+++ b/gdb/gdbarch-gen.h
@@ -433,14 +433,31 @@ extern void set_gdbarch_integer_to_address (struct gdbarch *gdbarch, gdbarch_int
    If WRITEBUF is not NULL, it contains a return value which will be
    stored into the appropriate register.  This can be used when we want
    to force the value returned by a function (see the "return" command
-   for instance). */
+   for instance).
 
-extern bool gdbarch_return_value_p (struct gdbarch *gdbarch);
+   NOTE: it is better to implement return_value_as_value instead, as that
+   method can properly handle variably-sized types. */
 
 typedef enum return_value_convention (gdbarch_return_value_ftype) (struct gdbarch *gdbarch, struct value *function, struct type *valtype, struct regcache *regcache, gdb_byte *readbuf, const gdb_byte *writebuf);
 extern enum return_value_convention gdbarch_return_value (struct gdbarch *gdbarch, struct value *function, struct type *valtype, struct regcache *regcache, gdb_byte *readbuf, const gdb_byte *writebuf);
 extern void set_gdbarch_return_value (struct gdbarch *gdbarch, gdbarch_return_value_ftype *return_value);
 
+/* Return the return-value convention that will be used by FUNCTION
+   to return a value of type VALTYPE.  FUNCTION may be NULL in which
+   case the return convention is computed based only on VALTYPE.
+
+   If READ_VALUE is not NULL, extract the return value and save it in
+   this pointer.
+
+   If WRITEBUF is not NULL, it contains a return value which will be
+   stored into the appropriate register.  This can be used when we want
+   to force the value returned by a function (see the "return" command
+   for instance). */
+
+typedef enum return_value_convention (gdbarch_return_value_as_value_ftype) (struct gdbarch *gdbarch, struct value *function, struct type *valtype, struct regcache *regcache, struct value **read_value, const gdb_byte *writebuf);
+extern enum return_value_convention gdbarch_return_value_as_value (struct gdbarch *gdbarch, struct value *function, struct type *valtype, struct regcache *regcache, struct value **read_value, const gdb_byte *writebuf);
+extern void set_gdbarch_return_value_as_value (struct gdbarch *gdbarch, gdbarch_return_value_as_value_ftype *return_value_as_value);
+
 /* Return the address at which the value being returned from
    the current function will be stored.  This routine is only
    called if the current function uses the the "struct return