[PATCH] gdb/amdgpu: provide dummy implementation of gdbarch_return_value_as_value

[Simon Marchi <simon.marchi@polymtl.ca>]

The AMD GPU support has been merged shortly after commit 4e1d2f5814b2
("Add new overload of gdbarch_return_value"), which made it mandatory
for architectures to provide either a return_value or
return_value_as_value implementation.  Because of my failure to test
properly after rebasing and before pushing, we get this with the current
master:

    $ gdb ./gdb -nx --data-directory=data-directory -q -ex "set arch amdgcn:gfx1010" -batch
    /home/simark/src/binutils-gdb/gdb/gdbarch.c:517: internal-error: verify_gdbarch: the following are invalid ...
            return_value_as_value

I started trying to change GDB to not force architectures to provide a
return_value or return_value_as_value implementation, but Andrew pointed
out that any serious port will have an implementation one day or
another, and it's easy to add a dummy implementation in the mean time.
So it's better to not complicate the core of GDB to know how to deal
with this.

There is an implementation of return_value in the downstream ROCgdb port
(which we'll need to convert to the new return_value_as_value), which
we'll contribute soon-ish.  In the mean time, add a dummy implementation
of return_value_as_value to avoid the failed assertion.

Change-Id: I26edf441b511170aa64068fd248ab6201158bb63
---
 gdb/amdgpu-tdep.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/gdb/amdgpu-tdep.c b/gdb/amdgpu-tdep.c
index 7f0e9dffab37..d681d9d6a504 100644
--- a/gdb/amdgpu-tdep.c
+++ b/gdb/amdgpu-tdep.c
@@ -51,6 +51,16 @@ get_amdgpu_gdbarch_tdep (gdbarch *arch)
   return gdbarch_tdep<amdgpu_gdbarch_tdep> (arch);
 }
 
+/* Dummy implementation of gdbarch_return_value_as_value.  */
+
+static return_value_convention
+amdgpu_return_value_as_value (gdbarch *arch, value *function, type *valtype,
+			      regcache *regcache, value **read_value,
+			      const gdb_byte *writebuf)
+{
+  gdb_assert_not_reached ("not implemented");
+}
+
 /* Return the name of register REGNUM.  */
 
 static const char *
@@ -1195,6 +1205,8 @@ amdgpu_gdbarch_init (struct gdbarch_info info, struct gdbarch_list *arches)
 
   set_gdbarch_dwarf2_reg_to_regnum (gdbarch, amdgpu_dwarf_reg_to_regnum);
 
+  set_gdbarch_return_value_as_value (gdbarch, amdgpu_return_value_as_value);
+
   /* Register representation.  */
   set_gdbarch_register_name (gdbarch, amdgpu_register_name);
   set_gdbarch_register_type (gdbarch, amdgpu_register_type);

base-commit: 1d6653fd3f4e0d7140e705733412fd75c40177b2
-- 
2.39.2